other realms – Page 4 – Center for Invasive Species Prevention

Australia Builds Capacity to Address Forest Pests

Australian Eucalypts; photo by John Turnbull via Flickr

I congratulate Australian scientists for bringing about substantial improvements of their country’s biosecurity program for forest pests. While it is too early to know how effective the changes will be in preventing new introductions, they are promising. What can we Americans learn from the Australian efforts? [I have previously praised South Africa’s efforts – there is much to learn there, too.]

Australia has a reputation of being very active in managing the invasive species threat. However, until recently biosecurity programs targetting forest pests were minimal and ad hoc. Scientists spent 30 years trying to close those gaps (Carnegie et al. 2022). Their efforts included publishing several reports or publications (listed at the end of the blog) and an international webinar on myrtle rust. Scientists are hopeful that the new early detection program (described below) will greatly enhance forest protection. However, thorough pest risk assessments are still not routinely conducted for forest pests. (Nahrung and Carnegie 2022).

The native flora of Australia is unique. That uniqueness has provided protection because fewer of the non-native insects and pathogens familiar to us in the Northern Hemisphere have found suitable hosts (Nahrung and Carnegie 2020). Also – I would argue – the uniqueness of this flora imposes a special responsibility to protect it from threats that do arise.

Only 17% of Australia’s landmass is covered by forests. Australia is large, however; consequently, these forests cover 134 million hectares (Nahrung and Carnegie 2020). This is the 7th largest forest estate in the world (Carnegie et al. 2022).

Australia’s forests are dominated by eucalypts (Eucalyptus, Corymbia and Angophora). These cover 101 million ha; or 75% of the forest). Acacia (11 million ha; 8%); and Melaleuca (6 million ha) are also significant. The forest also includes one million ha of plantations dominated by Pinus species native to North America (Carnegie et al. 2022). A wide range of native and exotic genera have been planted as amenity trees in urban and peri-urban areas, including pines, sycamores, poplars, oaks, and elms (Carnegie et al. 2022). These urban trees are highly valued for their ecosystem services as well as social, cultural, and property values (Nahrung and Carnegie 2020). Of course, these exotic trees can support establishment and spread of the forest pest species familiar to us in the Northern Hemisphere. On the positive side, they can also be used as sentinel plantings for early detection of non-native species (Carnegie et al. 2022 and Nahrung and Carnegie 2020).

Despite Australia’s geographic isolation, its unique native flora, and what is widely considered to be one of the world’s most robust biosecurity system, at least 260 non-native arthropods and pathogens of forests have established in Australia since 1885 (Nahrung and Carnegie 2020). [(This number is about half the number of non-native forest insects and pathogens that have established in the United States over a period just 25 years longer (Aukema et al. 2010).] As I noted, forest scientists have cited these introductions as a reason to strengthen Australia’s biosecurity system specifically as it applies to forest pests.

What steps have been taken to address this onslaught? For which pests? With what impacts? What gaps have been identified?

Which Pests?

Nahrung and Carnegie (2020) compiled the first comprehensive database of tree and forest pests established in Australia. The 260 species of non-native forest insect pests and pathogens comprise 143 arthropods, 117 pathogens. Nineteen of them (17 insects and 2 fungal species) had been detected before 1900. These species have accumulated at an overall rate of 1.9 species per year; the rate of accumulation after 1955 is slightly higher than during the earlier period, but it has not grown at the exponential rate of import volumes.

While over the entire period insects and pathogens were detected at an almost equal rate (insects at 1.1/year; pathogens at 0.9/year), this disguises an interesting disparity: half of the arthropods were detected before 1940; half of the pathogens after 1960 (Nahrung and Carnegie (2020). By 2022, Nahrung and Carnegie (2022) said that, on average, one new forest insect is introduced each year. Some of these recently detected organisms have probably been established for years. More robust surveillance has just detected them recently. I have blogged often about an apparent explosion of pathogens being transported globally in recent decades.

In a more recent article (Nahrung and Carnegie, 2022), gave 135 as the number of non-native forest insect pests. The authors don’t explain why this differs from the 143 arthropods listed before.

damage to pine plantations caused by *Sirex noctilio*; photo courtesy of Helen Nahrung

Eighty-seven percent of the established alien arthropods are associated with non-native hosts (e.g., Pinus, Platanus, Populus, Quercus, Ulmus) (Carnegie et al. 2022). Some of these have escaped eradication attempts and caused financial impact to commercial plantations (e.g., sirex wood wasp, Sirex noctilio) and amenity forests (e.g., elm leaf beetle, Xanthogaleruca luteola) (Carnegie and Nahrung 2019).

About 40% of the alien arthropods were largely cosmopolitan at the time of their introduction in Australia (Carnegie et al. 2022). Only six insects and six fungal species are not recorded as invasive elsewhere (Nahrung and Carnegie 2020). Of the species not yet established, 91% of interceptions from 2003 to- 2016 were known to be invasive elsewhere. There is strong evidence of the bridgehead effect: 95% of interceptions of three species were from their invaded range (Nahrung and Carnegie 2022). These included most of the insects detected in shipments from North America, Europe and New Zealand. These ubiquitous “superinvaders” have been circulating in trade for decades and continue to be intercepted at Australia’s borders. This situation suggests that higher interception rates of these species reflect their invasion success rather than predict it (Nahrung and Carnegie 2021).

I find it alarming that most species detected in shipments from Africa, South America, and New Zealand were of species not even recorded as established in those regions (Nahrung and Carnegie 2021; Nahrung and Carnegie 2022).

*Arhopalus ferus*, a Eurasian pine insect often detected in wood from New Zealand; photo by Jon Sullivan – in New Zealand; via Flickr

Half of the alien forest pests established in Australia are highly polyphagous. This includes 73% of Asian-origin pests but only 15% of those from Europe (Nahrung and Carnegie 2021). Nahrung and Carnegie (2022) confirm that polyphagous species are more likely to be detected during border inspections.

PATHWAYS

As in North America and Europe, introductions of Hemiptera are overwhelmingly (98%) associated with fresh plant material (e.g. nursery stock, fruit, foliage). Coleoptera introductions are predominantly (64%) associated with wood (e.g. packaging, timber, furniture, and artefacts). Both pathways are subject to strict regulations by Australia (Nahrung and Carnegie 2021).

Eradication of High-Priority Pests

Eight-five percent of all new detections were not considered high-priority risks. Of the four that were, two had not previously been recognized as threats (Carnegie and Nahrung 2019). One high-priority pest – expected to pose a severe threat to at least some of Australia’s endemic plant species – is myrtle rust, Austropuccinia psidii. Despite this designation, when the rust appeared in Australia in 2010, the response was confused and ended in an early decision that eradication was impossible. Myrtle rust has now spread along the continent’s east coast, with localized distribution in Victoria, Tasmania, the Northern Territory, and – in 2022, Western Australia. `

*Melaleuca quinquenervia* forest; photo by Doug Beckers via Wikimedia

There have been significant impacts to native plant communities. Several reviews of the emergency response criticized the haste with which the initial decision was made to end eradication (Carnegie and Nahrung 2019). (A review of these impacts is here; unfortunately, it is behind a paywall.)

A second newly introduced species has been recognized as a significant threat, but only after its introduction to offshore islands. This is Erythina gall wasp Quadrastichus erythrinae (Carnegie and Nahrung 2019). DMF Although Australia is home to at least one native species in the Erythrina genus, E. vespertilio,, the gall wasp is not included on the environmental pest watch list.

Four of the recently detected species were considered to be high impact. Therefore eradication was attempted. Unfortunately, these attempts failed in three cases. The single success involved a pinewood nematode, Bursaphelenchus hunanesis. See Nahrung and Carnegie (2021) for a discussion of the reasons. This means three species recognized as high-impact pests have established in Australia over 15 years (Nahrung and Carnegie (2021). In fact, Australia’s record of successful forest pest eradications is only half the global average (Carnegie and Nahrung (2019).

Carnegie and Nahrung (2019) conclude that improving early detection strategies is key to increasing the likelihood of eradication. They discuss the strengths and weaknesses of various strategies. Non-officials (citizen scientists) reported 59% of the 260 forest pests detected (Carnegie and Nahrung 2019). Few alien pests have been detected by official surveillance (Carnegie et al 2022). However, managing citizen scientists’ reports involves a significant workload. Futhermore, surveillance by industry, while appreciated, is likely to detect only established species (Carnegie and Nahrung 2019).

Interception Frequency Is Not an Indicator of Likelihood of Establishment

Nahrung & Carnegie (2021) document that taxonomic groups already established in Australia are rarely detected at the border. Furthermore, only two species were intercepted before they were discovered to be established in Australia.

Indeed, 76% of species established in Australia were either never or rarely intercepted at the border. While more Hemiptera species are established in Australia, significantly more species of Coleoptera are intercepted at the border. Among beetles, the most-intercepted family is Bostrichid borers (powderpost beetles). Over the period 2003 – 2016, Bostrichid beetles made up 82% of interceptions in wood packaging and 44% in wood products (Nahrung and Carnegie 2022). This beetle family is not considered a quarantine concern by either Australian or American phytosanitary officials. I believe USDA APHIS does not even bother recording detections of powderpost beetles. Nahrung and Carnegie (2021) think the high proportion of Bostrichids might be partially explained by intense inspection of baggage, mail, and personal effects. While Australia actively instructs travelers not to bring in fruits and vegetables because of the pest risk, there are fewer warnings about risks associated with wood products.

Nahrung & Carnegie (2021) concluded that interception frequencies did not provide a good overall indicator of likelihood of risk of contemporaneous establishment.

Do Programs Focus on the Right Species?

Although Hemiptera comprise about a third of recent detections and establishments, and four of eight established species are causing medium-to-high impact, no Hemiptera are currently listed as high priority forestry pests by Australian phytosanitary agencies (Nahrung & Carnegie (2021). On the other hand, Lepidoptera make up about a third of the high-priority species, yet only two have established in Australia over 130 years. Similarly, Cerambycidae are the most frequently intercepted forest pests and several are listed as high risk. But only three forest-related species have established (Nahrung and Carnegie 2020). (Note discussion of Bostrichidae above.).

Unlike the transcontinental exchanges under way in the Northern Hemisphere, none of the established beetles is from Asia; all are native to Europe. This is especially striking since interceptions from Asia-Pacific areas account for more than half of all interceptions Nahrung and Carnegie (2021).

Interestingly, 32 Australian Lepidopteran and eight Cerambycid species are considered pests in New Zealand. However, no forest pests native to New Zealand have established in Australia despite high levels of trade, geographic proximity, and the high number of shared exotic tree forest species (Nahrung and Carnegie 2020).

STRUCTURE OF PROGRAM

The structure of Australia’s plant biosecurity system is described in detail in Carnegie et al. (2022). These authors call the program “comprehensive” but to me it looks highly fragmented. The federal Department of Agriculture and Water Resources (DAWR,[recently renamed the Department of Agriculture, Fisheries, and Forestry, or DAFF) is responsible for pre-border (e.g., off-shore compliance) and border (e.g., import inspection) activities. The seven state governments, along with DAFF, are responsible for surveillance within the country, management of pest incursions, and regulation of pests. Once an alien pest has become established, its management becomes the responsibility of the land manager. In Australia, then, biosecurity is considered to be a responsibility shared between governments, industry and individuals.

Even this fragmented approach was developed more recently than one might expect given Australia’s reputation for having a stringent biosecurity system. Perhaps this reflects the earlier worldwide neglect of the Plant Kingdom? Carnegie and Nahrung (2019) describe recent improvements. Until the year 2000, Australia’s response to the detection of exotic plant pests was primarily case-by-case. In that year Plant Health Australia (PHA) was incorporated. Its purpose was to facilitate preparedness and response arrangements between governments and industry for plant pests. In 2005, the Emergency Plant Pest Response Deed (EPPRD) was created. It is a legally-binding agreement between the federal, state, and territorial governments and plant industry bodies. As of 2022, 38 were engaged. It sets up a process to implement management and funding of agreed responses to the detection of exotic plant pests – including cost-sharing and owner reimbursement. A national response plan (PLANTPLAN) provides management guidelines and outlines procedures, roles and responsibilities for all parties. A national committee (Consultative Committee on Emergency Plant Pests (CCEPP) works with surveys to determine invaded areas (delimitation surveys) and other data to determine whether eradicating the pest is technically feasible and has higher economic benefits than costs..

*Austropuccinia psidii* on *Melaleuca quinquenervia*; photo by John Tann via Flickr

Even after creation of EPPRD in 2005, studies revealed significant gaps in Australia’s post-border forest biosecurity systems regarding forest pests (Carnegie et al. 2022; Carnegie and Nahrung 2019). These studies – and the disappointing response to the arrival of myrtle rust – led to development of the National Forest Biosecurity Surveillance Strategy (NFBSS) – published in 2018; accompanied by an Implementation Plan. A National Forest Biosecurity Coordinator was appointed.

The forest sector is funding a significant proportion of the proposed activities for the next five years; extension is probable. Drs. Carnegie and Nahrung are pleased that the national surveillance program has been established. It includes specific surveillance at high-risk sites and training of stakeholders who can be additional eyes on the ground. The Australian Forest Products Association has appointed a biosecurity manager (pers. comm.)

This mechanism is expected to ensure that current and future needs of the plant biosecurity system can be mutually agreed on, issues identified, and solutions found. Plant Health Australia’s independence and impartiality allow the company to put the interests of the plant biosecurity system first. It also supports a longer-term perspective (Carnegie et al. (2022). Leading natural resource management organizations are also engaged (Carnegie, pers. comm.).

Presumably the forest surveillance strategy (NFBSS) structure is intended to address the following problems (Carnegie and Nahrung 2019):

Alien forest pests are monitored offshore and at the border, but post-border surveillance is less structured and poorly resourced. Australia still lacks a surveillance strategy for environmental pests.
Several plant industries have developed their own biosecurity programs, co-funded by the government. These include the National Forest Biosecurity Surveillance Strategy (NFBSS).

Some pilot projects targetting high risk sites were initiated in the early 2000s. By 2019, only one surveillance program remained — trapping for Asian spongy (gypsy) moth.

The states of Victoria and New South Wales have set up sentinel site programs. Victoria’s uses local council tree databases. It is apparently focused on urban trees and is primarily pest-specific – e.g., Dutch elm disease. The New South Wales program monitors more than 1,500 sentinel trees and traps insects near ports. This program is funded by a single forest grower through 2022.

Dr. Carnegie states: “With the start of the national forest biosecurity surveillance program in December 2022, the issues and gaps identified by Carnegie et al. 2022 are starting to be addressed. The program will conduct biosecurity surveillance specifically for forest pests and pathogens and be integrated with national and state biosecurity activities. While biosecurity in Australia is still agri-centric, a concerted and sustained effort from technical experts from the forest industry is changing this. And finally, the new Biosecurity Levy should ensure sustained funding for biosecurity surveillance.”

There is a separate National Environmental Biosecurity Response Agreement (NEBRA), adopted in 2012. It is intended to provide guidelines for responding, cost-sharing arrangements, etc. when the alien pest threatens predominantly the environment or public amenity assets (Carnegie et al. (2022). However, when the polyphagous shot hole borer was detected, the system didn’t work as might have been expected. While PSHB had previously been identified as an environmental priority pest, specifically to Acacia, the decision whether to engage was made under auspices of the the Emergency Plant Pest Response Deed (EPPRD) rather than the environmental agreement (NEBRA). As a result, stakeholders focused on environmental, amenity and indigenous concerns had no formal representation in decision-making processes; instead, industries that had assessed the species as a low priority (e.g., avocado and plantation forestry) did (Nahrung, pers.comm.).

Additional Issues Needing Attention

Some needs are not addressed by the National Forest Pest Strategic Plan (Carnegie et al. 2022) (Nahrung, pers. comm.):

1) The long-term strategic investment from the commercial forestry sector and government needed to maintain surveillance and diagnostic expertise;

2) Studies to assess social acceptance of response and eradication activities such as tree removal;

3) Studies to improve pest risk prioritization and assessment methods; and

4) Resolving the biosecurity responsibilities for pests of timber that has been cut and used in construction.

In 2019, Carnegie and Nahrung (2019) called for developing more effective methods of detection, especially of Hemiptera and pathogens. They also promoted national standardization of data collection. Finally, they advocated inclusion of technical experts from state governments, research organizations and industry in developing and implementing responses to pest incursions. They note that surveillance and management programs must be prepared to expect and respond to the unexpected since 85% of the pests detected over the last 20 years—and 75% of subsequently mid-to high-impact species established—were not on high-priority pest list. See Nahrung and Carnegie 2022 for a thorough discussion of the usefulness and weaknesses of predictive pest listing.

SOURCES

Aukema, J.E., D.G. McCullough, B. Von Holle, A.M. Liebhold, K. Britton, & S.J. Frankel. 2010. Historical Accumulation of Nonindigenous Forest Pests in the Continental United States. Bioscience. December 2010 / Vol. 60 No. 11

Carnegie A.J. and H.F. Nahrung. 2019. Post-Border Forest Biosecurity in AU: Response to Recent Exotic Detections, Current Surveillance and Ongoing Needs. Forests 2019, 10, 336; doi:10.3390/f10040336 www.mdpi.com/journal/forests

Carnegie A.J., F. Tovar, S. Collins, S.A. Lawson, and H.F. Nahrung. 2022. A Coordinated, Risk-Based, National Forest Biosecurity Surveillance Program for AU Forests. Front. For. Glob. Change 4:756885. doi: 10.3389/ffgc.2021.756885

Nahrung H.F. and A.J. Carnegie. 2020. NIS Forest Insects and Pathogens in Australia: Establishmebt, Spread, and Impact. Frontiers in Forests and Global Change 3:37. doi: 10.3389/ffgc.2020.00037 March 2020 | Volume 3 | Article 37

Nahrung, H.F. and A.J. Carnegie. 2021. Border interceps of forest insects estab in AU: intercepted invaders travel early and often. NeoBiota 64: 69–86. https://doi.org/10.3897/neobiota.64.60424

Nahrung, H.F. & A.J. Carnegie. 2022. Predicting Forest Pest Threats in Australia: Are Risk Lists Worth the Paper they’re Written on? Global Biosecurity, 2022; 4(1).

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

www.fadingforests.org

Tree Planting – Warning from New Zealand

*Pinus radiata* plantation in New Zealand; photo by Jon Sullivan

As countries and conservation organizations ramp up tree planting as one solution to climate change, I worry that many of the plantings will use species not native to the region – with the risk of promoting more bioinvasions. My second fear is that inadequate attention will be paid to ensuring that the propagules thrive.

Warning from New Zealand

New Zealand has adopted a major afforestation initiative (“One Billion Trees”). This program is ostensibly governed by a policy of “right tree, right place, right purpose”. However, Bellingham et al. (2022) [full citation at end of blog] say the program will probably increase the already extensive area of radiata pine plantations and thus the likelihood of exacerbated invasion. They say the species’ potential invasiveness and its effects in natural ecosystems have not been considered.

Bellingham et al. set out to raise the alarm by evaluating the current status of radiata, or Monterrey, pine (Pinus radiata) in the country. They note that the species already occupies ~1.6 M ha; the species makes up 90% of the country’s planted forests. Despite the species having been detected as spreading outside plantations in 1904, it is generally thought not to have invaded widely.

The authors contend that, to the contrary, radiata pine has already invaded several grasslands and shrublands, including three classes of ecosystems that are naturally uncommon. These are geothermal ecosystems, gumlands (infertile soils that formerly supported forests dominated by the endemic and threatened kauri tree Agathis australis), and inland cliffs. Invasions by pines – including radiata pine – are also affecting primary succession on volcanic substrates, landslides on New Zealand’s steep, erosion-prone terrain, and coastal sand dunes. Finally, pine invasions are overtopping native Myrtaceae shrubs during secondary succession. Bellingham et al. describe the situation as a pervasive and ongoing invasion resulting primarily from spread from plantations to relatively nearby areas.

kauri; photo by Natalia Volna, iTravelNZ

The New Zealanders cite data from South America and South Africa on the damaging effects of invasions by various pine species, especially with respect to fire regimes.

Furthermore, their modelling indicates that up to 76% of New Zealand’s land area is climatically capable of supporting radiata pine — most of the country except areas above 1000 m in elevation or receiving more than 2000 mm of rainfall per year. That is, all but the center and west of the South Island. This model is based on current climate; a warmer/drier climate would probably increase the area suitable to radiata pine.

These invasions by radiata pine have probably been overlooked because the focus has been on montane grasslands (which are invaded by other species of North American conifers). [See below — surveys of knowledge of invasive plants’ impacts.]

Bellingham et al. recognize the economic importance of radiata pine. They believe that early detection of spread from plantations and rapid deployment of containment programs would be the most effective management strategy. They therefore recommend

1) taxing new plantations of non-indigenous conifers to offset the costs of managing invasions, and

2) regulating these plantations more strictly to protect vulnerable ecosystems.

They also note several areas where additional research on the species’ invasiveness, dispersal, and impacts is needed.

Survey of Awareness of Invasive Plants

A few months later a separate group of New Zealand scientists published a study examining tourists’ understanding of invasive plant impacts and willingness to support eradication programs (Lovelock et al.; full citation at end of the blog). One of the invasive plant groups included in the study are conifers introduced from North America and Europe. These conifers are invading montane grasslands, so they are not the specific topic of the earlier article. The other is a beautiful flowering plant, Russell lupine. These authors say that both plant groups have profound ecological, economic, and environmental impacts. However, the conifers and lupines are also highly visible at places valued by tourists. Lovelock et al. explored whether the plants’ familiarity – and beauty – might affect how people reacted to descriptions of their ecosystem impacts.

Visitors from elsewhere in New Zealand were more aware of invasive plants’ impacts and more willing to support eradication programs for these species specifically. Asian visitors had lower awareness and willingness to support eradication of the invasives than tourists from the United Kingdom, Europe, or North America. This pattern remained after the tourists were informed about the plants’ ecological impacts. All groups were less willing to support eradication of the attractive Russell lupine than the conifers.

Conifers invading montane grasslands are perhaps the most publicized invasive plants in New Zealand [as noted above]. Lovelock et al. report that New Zealand authorities have spent an estimated $NZ166 million to eradicate non-native conifers over large tracts of land on the South Island. Still, only about half the New Zealand visitors surveyed were aware of the ecological problems caused by wild conifers.

Russell lupine (Lupinus × russellii) is invading braided river systems, modifying river flows, reducing nesting site availability for several endangered birds, and provides cover for invasive predators. While initially planted in gardens, the lupines were soon being deliberately spread along the roads to ‘beautify’ the landscape. Foreign tourists often specifically seek river valley invaded by the lupine because pictures of the floral display appear in both official tourism promotional material & tourist-related social media. It is not surprising, then, that even among New Zealanders, only a third were aware of the lupines’ environmental impacts.

The oldest participants (those over 60) had the lowest acceptance of wild conifers. Participants 50–59 years old were most aware of ecological problems caused by wild conifers. Participants 30–39 years old showed the highest acceptance of wild conifers and lowest awareness of ecological issues.

Female participants showed a higher preference for the landscape with wild conifers (45.90%) than males (36.89%). Female participants were also half as aware of ecological problems (25.62% v. 46.12% among male participants).

Nearly all survey participants (96.1%) preferred the landscape with flowering lupine; only 19.4% were aware of associated ecological problems. New Zealand domestic visitors were more aware. After the impacts of lupines were explained, half decided to support eradication. However, the same proportion of all survey participants (42.5%) still wanted to see lupines in the landscape.

Once again, participants older than 50 were more aware of ecological problems arising from lupine invasions. Both men and women greatly preferred the landscape with Russell lupins.

While the authors do not explore the ramifications of the finding that younger people are less aware of invasive species impacts, I think they bode ill for future protection of the country’s unique flora and fauna. They did note that respondents had a high level of acceptance overall for these species on the New Zealand landscapes.

While the study supported use of simple environmental messaging to influence attitudes about invasive species, also showed that need to consider such social attributes as nationality and ethnicity. So Lovelock et al. call for investigation of how and why place of origin and ethnicity are important in shaping attitudes towards invasives. Conveying conservation messages will be more difficult because tourist materials often contain photographs of the lupines. Much of this information comes from informal media such as social media, which are beyond the control of invasive species managers.

SOURCES

Bellingham, P.J., E.A. Arnst, B.D. Clarkson, T.R. Etherington, L.J. Forester, W.B. Shaw, R. Sprague, S.K. Wiser, and D.A. Peltzer. 2022. The right tree in the right place? A major economic tree species poses major ecological threats. Biol Invasions Vol.: (0123456789) https://doi.org/10.1007/s10530-022-02892-6

Lovelock B., Y. Ji, A. Carr, and C-J. Blye. 2022. Should tourists care more about invasive species? International and domestic visitors’ perceptions of invasive plants and their control in New Zealand. Biological Invasions (2022) 24:3905–3918 https://doi.org/10.1007/s10530-022-02890-8

Posted by Faith Campbell

www.fadingforests.org

Boxwood Blight – Another Failure of the Global Phytosanitary System

boxwood garden at Gunston Hall – home of founding father George Mason; Virginia; photo by Roger 4336 *via* Wikimedia

Boxwood blight is a disease caused by a group of fungal pathogens. While boxwoods are horticultural plants in the U.S. – important ones! – they are keystone forest species in several regions of the tropics and subtropics.

The situation with boxwood blight is yet another example of a too-frequent pattern for plant pathogens. This pattern applies even to plant taxa that are important to the ornamental horticulture industry – not only plants that are important in natural ecosystems. [See other blogs posted here under the category “plants as pest vectors”, e.g., here. The boxwood blight pathogens:

are of unknown origin;
have a wide range of known hosts; additional hosts probable;
have been introduced to many new sites over about 30 years;
have caused considerable economic, aesthetic, and ecological harm;
are a threat to centers of endemism;
have no known methods to treat plants in forests;
are spread by international plant trade;
complicate detection by having hosts that sometimes are asymptomatic; or symptoms can be suppressed by fungicides;
apparently few efforts to apply phytosanitary measures to prevent further spread.

Also typical: concerned scientists are trying to promote adoption of phytosanitary measures. This takes the form of a study by Barke, Coop and Hong (full citation at the end of the blog; unless otherwise stated, information in this blog is from this source). They use several models based largely on climatic factors to predict additional geographic areas where else boxwood blight might establish.

I think it is most unfortunate that the U.S. horticultural industry prefers to avoid federal regulation despite the significant costs to its members. Instead, it has advocated for a primarily voluntary response (see below). This undermines efforts to restructure regulatory programs to improve phytosanitary agencies’ management of pathogens. Since the U.S. is such a powerful player on this issue, reducing pressure on APHIS to find more effective measures has global implications. I recognize that preventing transmission of unknown and cryptic pathogens is an intrinsically difficult task. However, tackling this problem should be a top priority for people concerned about retaining healthy floral communities.

Specifics About Boxwood Blight

Boxwood blight is caused by two ascomycete fungi, Calonectria pseudonaviculata [synonym Cylindrocladium buxicola] and Calonectria henricotiae. Both can infect and blight boxwood foliage, resulting in rapid plant death. C. henricotiae is known from only five countries in Europe; C. pseudonaviculata is currently established in 24 countries in three geographic areas: Europe and western Asia; New Zealand; and North America (30 US states and British Columbia). The disease caused by C. pseudonaviculata could spread well beyond its currently invaded range in these regions.

range of *Buxus sempervirens*; via Wikimedia

Native plants in the family Buxaceae grow in tropical or subtropical areas around the world. Plants in the genera Buxus, Didymeles, Haptanthus, Pachysandra, Sarcococca, and Styloceras are found in some areas of western and southern Europe; Turkey and the Caucuses into Iran; several countries in southeast and east Asia (China, Japan, South Korea, Vietnam, Indonesia); coastal Australia; high elevation areas of Africa, including Madagascar; parts of South America (southern Brazil, Uruguay, northern Argentina, and southern Chile, and foothills of the Andes); parts of Central America and the Caribbean. Asia is home to about 40 species of Buxus, four species of Pachysandra, and 11 species of Sarcococca. In the Andes region, all five species of Styloceras are endemic. Central America and the Caribbean are home to about 50 species of Buxus; there are 37 species endemic to Cuba! Madagascar has nine endemic Buxus species.

Many Buxus species occur in small and isolated distributions resulting from both natural causes (e.g., island endemism) and anthropogenic disturbances (including deforestation and invasions of by other non-native pests, such as the box tree moth Cydalima perspectalis in Europe and western Asia).

In native stands of Buxus sempervirens in Georgia and northern Iran, where C. pseudonaviculata was detected in 2010, the disease has caused rapid and intensive defoliation of boxwood plants of different ages. [See also Lehtijarvi, Dogmus-Lehtijarvi and Oskay. Boxwood Blight in Turkey: Impact on Natural Boxwood Populations and Management Challenges. Baltic Forestry 2017, vol. 23(1)] Infected plants are also vulnerable to attacks by secondary opportunistic pathogens that can lead to eventual death. Damage to these forests could lead to reductions in soil stability and subsequent declines in water quality and flood protection, changes in forest structure and composition, and declines in Buxus-associated biodiversity (at least 63 species of lichens, fungi, chromista and invertebrates might be obligate).

Barke, Coop and Hong expect excessive heat and seasonal dryness at one extreme and excessive cold at the other to limit areas in North America and Europe/central Asia where the disease can establish. Areas with oceanic rather than continental climates are probably more vulnerable. However, heat and aridity barriers could be overcome by artificial irrigation of horticultural plantings.

Indeed, the conditions favoring C. pseudonaviculata establishment – warm temperatures and high humidity or water on the leaves – are commonly found in production nurseries. Overhead irrigation exacerbates the risk. Production nurseries also have large numbers of host plants in close proximity – so it is easy for disease to spread (Douglas).

I am reminded that the causal agent of sudden oak death, Phytophthora ramorum, has been spread from production nurseries located in hot, dry areas that were considered unsuitable to the pathogen – because conditions inside the nursery were suitable.

wild *Buxus* on island of Corsica; photo by Sten Porse *via* Wikimedia

As I noted, the origin of C. pseudonaviculata is unknown. Barke, Coop and Hong think it is most likely in eastern Asia, which is thought to be the likely native region of box tree moth. However, they cannot rule out some other center of diversity for Buxaceae species e.g., the Caribbean or Madagascar.

Barke, Coop and Hong call for additional studies to

Explore potential effects of climate change on establishment risk, especially higher latitude areas expected to see increasing humidity, precipitation, and rising temperatures.
Determine ability of C. pseudonaviculata microsclerotia to survive higher temperatures, e.g. in parts of the U.S. Deep South that may have ideal growing conditions during cool seasons.
Modify the CLIMEX model developed for this study to predict the potential distribution of C. henricotiae, a closely related but genetically distinct species with greater tolerance of higher temperatures.

They call for a strict phytosanitary protocol for risk mitigation of accidental intro, with effective surveillance for early detection, and development of a recovery plan.

Regulatory (non) Response

Boxwood blight was first detected in the United Kingdom in mid-1990s; then in New Zealand in 2002. Only then was the causal agent determined. It was first detected in the U.S. in October 2011 (in Connecticut). It was quickly determined to be established in the mid-Atlantic region. Apparently the British, other European countries, and APHIS all decided the pathogen was too widespread to regulate (Douglas).

The U.S. is relying on a voluntary program. The nursery industry, through its Horticultural Research Institute (HRI), and the National Plant Board developed guidance for best management practices – updated as recently as 2020.

boxwood blight symptoms; Oregon State University; *via* Flickr

In contrast, APHIS has acted to regulate the boxwood tree moth, Cydalima perspectalis. The moth was first detected in North America near Toronto in 2018. U.S. nurseries in six states received infected plants in spring 2021. On May 26, 2021, APHIS prohibited importation of host plants from Canada, including boxwood (Buxus spp), Euonymus (Euonymus spp), and holly (Ilex spp).

In July 2021, the moth was detected in Niagara County, New York. It was thought that the moths had flown or been blown into the area from Canada. New York adopted an intrastate quarantine of three counties (Erie, Niagara, and Orleans) in December 10, 2021. APHIS followed with an interstate quarantine on March 23, 2022.

SOURCES

Barke, B.S., L. Coop and C. Hong. 2022. Potential Distribution of Invasive Boxwood Blight Pathogen (Calonectria pseudonaviculata) as Predicted by Process-Based and Correlative Models. Biology 2022, 11, 849. https://doi.org/10.3390/biology11060849 www.mdpi.com/journal/biology

Douglas, S.M. Fact sheet; Connecticut Agricultural Experiment Station https://portal.ct.gov/-/media/CAES/DOCUMENTS/Publications/Fact_Sheets/Plant_Pathology_and_Ecology/2020/Boxwood-Blight-(1).pdf?la=en&hash=A4C6AF39765F27FDDEB5B4DC3FD3B6F3

Posted by Faith Campbell

www.fadingforests.org

Invasions cost protected areas more than $22 billion in 35 years

Burmese python in Everglades National Park; photo by Bob Reed, US FWS

Scientists continue to apply data collected in an international database (InvaCost; see “methods” section of Cuthbert et al.; full citation at end of this blog) to estimate the economic costs associated with invasive alien species (IAS). These sources reported $22.24 billion in economic costs of bioinvasion in protected areas over the 35-year period 1975 – 2020. Because the data has significant gaps, no doubt invasions really cost much more.

Moodley et al. 2022 (full citation at end of this blog) attempt to apply these data to analyze economic costs in protected areas. As they note, protected areas are a pillar of global biodiversity conservation. So it is important to understand the extent to which bioinvasion threatens this purpose.

Unfortunately, the data are still too scant to support any conclusions. Such distortions are acknowledged by Moodley et al. I will discuss the data gaps below a summary of the study’s findings.

The Details

Of the estimated $22.24 billion, only 4% were observed costs; 96% were “potential” costs (= extrapolated or predicted based on models). Both had generally increased in more recent years, especially “potential” costs after 1995. As is true in other analyses of InvaCost data, the great majority (73%) of observed costs covered management efforts rather than losses due to impacts. The 24% of total costs ascribed to losses, or damage, exceeded the authors’ expectation. They had thought that the minimal presence of human infrastructure inside protected areas would result in low records of “economic” damages.

The great majority (83%) of reported management costs were reactive, that is, undertaken after the invasion had occurred. In terrestrial environments, there were significantly higher bioinvasion costs inside protected areas than outside (although this varied by continent). However, when considering predicted or modelled costs, the importance was reversed: expected management costs represented only 5% while these “potential” damages were 94%.

Higher expenditures were reported in more developed countries – which have more resources to allocate and are better able to carry out research documenting both damage and effort.

More than 80% of management costs were shouldered by governmental services and/or official organizations (e.g. conservation agencies, forest services, or associations). The “agriculture” and “public and social welfare” sectors sustained 60% of observed “damage” and 89% of “mixed damage and management” costs respectively. The “environmental” and “public and social welfare” sectors together accounted for 94% of all the “potential” costs (predicted based on models) generated by invasive species in protected areas; 99% of damage costs. With the partial exception of the agricultural sector, the economic sectors that contribute the most to movement to invasive species are spared from carrying the resulting costs.

Lord Howe Island, Australia; threatened by myrtle rust; photo by Robert Whyte, *via* Flickr

Invasive plants dominated by numbers of published reports – 64% of reports of observed costs, 79% of reports of “potential”. However, both actual and “potential” costs allotted to plant invasions were much lower than for vertebrates and invertebrates. Mammals and insects dominated observed animal costs.

It is often asserted that protected areas are less vulnerable to bioinvasion because of the relative absence of human activity. Moodley et al. suggest the contrary: that protected areas might be more vulnerable to bioinvasion because they often host a larger proportion of native, endemic and threatened species less adapted to anthropogenic disturbances. Of course, no place on Earth is free of anthropogenic influences; this was true even before climate change became an overriding threat. Plenty of U.S. National parks and wilderness areas have suffered invasion by species that are causing significant change (see, for example, here, here, and here).

Despite Best Efforts, Data are Scant and Skewed

Economic data on invasive species in protected areas were available for only a tiny proportion of these sites — 55 out of 266,561 protected areas.

As Moodley et al. state, their study was hampered by several data gaps:

Taxonomic bias – plants are both more frequently studied and managed in protected areas, but their reported observed costs are substantially lower than those of either mammals or insects.
The data relate to economic rather than ecological effects. The costliest species economically might not cause the greatest ecological harm.
Geographical bias – studies are more plentiful in the Americas and Pacific Islands. However, studies from Europe, Africa and South America more often report observed costs. The South African attention to invasive species (see blogs here, here, and here), and economic importance of tourism to the Galápagos Islands exacerbate these data biases.
Methodological bias – although reporting bioinvasion costs has steadily increased, it is still erratic and dominated by “potential” costs = predictions, models or simulations.

I note that, in addition, individual examples of high-cost invasive species are not representative. The highest costs reported pertained to one agricultural pest (mango beetle) and one human health threat (mosquitoes).

Great Smokey Mountains National Park; threatened by mammals (pigs), forest pests, worms, invasive plants … Photo by Domenico Convertini *via* Flickr

As these weaknesses demonstrate, a significant need remains for increased attention to the economic aspects of bioinvasion – especially since political leaders pay so much greater attention to economics than to other metrics. However, the reported costs – $22.24 billion over 35 years, and growing! – are sufficient in the view of Moodley et al. to support advocating investment of more resources in invasive species management in protected areas, including – or especially – it is not quite clear — preventative measures.

SOURCES

Cuthbert, R.N., C Diagne, E.J. Hudgins, A. Turbelin, D.A. Ahmed, C. Albert, T.W. Bodey, E. Briski, F. Essl, P.J. Haubrock, R.E. Gozlan, N. Kirichenko, M. Kourantidou, A.M. Kramer, F. Courchamp. 2022. Bioinvasion cost reveals insufficient proactive management worldwide. Science of The Total Environment Volume 819, 1 May, 2022, 153404

Moodley, D., E. Angulo, R.N. Cuthbert, B. Leung, A. Turbelin, A. Novoa, M. Kourantidou, G. Heringer, P.J. Haubrock, D. Renault, M. Robuchon, J. Fantle-Lepczyk, F. Courchamp, C. Diagne. 2022. Surprisingly high economic costs of bioinvasions in protected areas. Biol Invasions. https://doi.org/10.1007/s10530-022-02732-7

Posted by Faith Campbell

or www.fadingforests.org

What Do Invasive Species Cost?

brown tree snake *Boiga irregularis*; via Wikimedia; one of the species on which the most money is spent on preventive efforts

In recent years a group of scientists have attempted to determine how much invasive species are costing worldwide. See Daigne et al. 2020 here.

Some of these scientists have now gone further in evaluating these data. Cuthbert et al. (2022) [full citation at end of blog] see management of steadily increasing numbers of invasive, alien species as a major societal challenge for the 21st Century. They undertook their study of invasive species-related costs and expenditures because rising numbers and impacts of bioinvasions are placing growing pressure on the management of ecological and economic systems and they expect this burden to continue to rise (citing Seebens et al., 2021; full citation at end of blog).

They relied on a database of economic costs (InvaCost; see “methods” section of Cuthbert et al.) It is the best there is but Cuthbert et al. note several gaps:

Only 83 countries reported management costs; of those, only 24 reported costs specifically associated with pre-invasion (prevention) efforts.
Data comparing regional costs do not incorporate consideration of varying purchasing power of the reporting countries’ currencies.
Data available are patchy so global management costs are probably substantially underestimated. For example, forest insects and pathogens account for less than 1% of the records in the InvaCost database, but constitute 25% of total annual costs ($43.4 billion) (Williams et al., in prep.) .

Still, their findings fit widespread expectations.

These data point to a total cost associated with invasive species – including both realized damage and management costs – of about $1.5 trillion since 1960. North America and Oceania spent by far the greatest amount of all global money countering bioinvasions. North America spent 54% of the total expenditure of $95.3 billion; Oceania spent 30%. The remaining regions each spent less than $5 billion.

Cuthbert et al. set out to compare management expenditures to losses/damage; to compare management expenditures pre-invasion (prevention) to post-invasion (control); and to determine potential savings if management had been more timely.

Economic Data Show Global Efforts Could Be – But Aren’t — Cost-Effective

The authors conclude that countries are making insufficient investments in invasive species management — particularly preventive management. This failure is demonstrated by the fact thatreported management expenditures ($95.3 billion) are only 8% of total damage costs from invasions ($1.13 trillion). While both cost or losses and management expenditures have risen over time, even in recent decades, losses were more than ten times larger than reported management expenditures. This discrepancy was true across all regions except the Antarctic-Subantarctic. The discrepancy was especially noteworthy in Asia, where damages were 77-times higher than management expenditures.

Furthermore, only a tiny fraction of overall management spending goes to prevention. Of the $95.3 billion in total spending on management, only $2.8 billion – less than 3% – has been spent on pre-invasion management. Again, this pattern is true for all geographic regions except the Antarctic-Subantarctic. The divergence is greatest in Africa, where post-introduction control is funded at more than 1400 times preventive efforts. It is also significant for Asia and South America.

Even in North America – where preventative actions were most generously funded – post-introduction management is funded at 16 times that of prevention.

Cuthbert et al. worry particularly about the low level of funding for prevention in the Global South. They note that these conservation managers operate under severe budgetary constraints. At least some of the bioinvasion-caused losses suffered by resources under their stewardship could have been avoided if the invaders’ introduction and establishment had been successfully prevented.

While in the body of the article Cuthbert et al. seem uncertain about why funding for preventive actions is so low, in their conclusions they offer a convincing (to me) explanation. They note that people are intrinsically inclined to react when impact becomes apparent. It is therefore difficult to motivate proactive investment when impacts are seemingly absent in the short-term, incurred by other sectors, or in different regions, and when other demands on limited funds may seem more pressing. Plus efficient proactive management will prevent any impact, paradoxically undermining evidence of the value of this action!

*Aedes aegypti* mosquito; one of the species on which the most money is spent for post-introduction control; photo by James Gathany; via Flickr

Delay Costs Money

The reports contained in the InvaCost database indicate that management is delayed an average of 11 years after damage was first been reported. Cuthbert et al. estimate that these delays have caused an additional cost of about $1.2 trillion worldwide. Each $1 of management was estimated to reduce damage by $53.5 in this study. This finding, they argue, supports the value of timely invasive species management.

They point out that the Supplementary Materials contain many examples of bioinvasions that entail large and sustained late-stage expenditures that would have been avoided had management interventions begun earlier.

Although Cuthbert et al. are not as clear as I would wish, they seem to recognize also that stakeholders’ varying perceptions of whether an introduced species is causing a detrimental “impact” might also complicate reporting – not just whether any management action is taken

Cuthbert et al. are encouraged by two recent trends: growing investments in preventative actions and research, and shrinking delays in initiating management. However, these hopeful trends are unequal among the geographic regions.

Which Taxonomic Groups Get the Most Money?

About 42% of management costs ($39.9 billion) were spent on diverse or unspecified taxonomic groups. Of the costs that were taxonomically defined, 58% ($32.1 billion) was spent on invertebrates [see above re: forest pests]; 27% ($14.8 billion) on plants; 12% ($6.7 billion) on vertebrates; and 3% ($1.8 billion) on “other” taxa, i.e. fungi, chromists, and pathogens. For all of these defined taxonomic groups, post-invasion management dominated over pre-invasion management.

When considering the invaded habitats, 69% of overall management spending was on terrestrial species ($66.1 billion); 7% on semi-aquatic species ($6.7 billion); 2% on aquatic species ($2.0 billion); the remainder was “diverse/unspecified”. For pre-invasion management (prevention programs), terrestrial species were still highest ($840.4 million). However, a relatively large share of investments was allocated to aquatic invaders ($624.2 million).

Considering costs attributed to individual species, the top 10 targetted for preventive efforts were four insects, three mammals, two reptiles, and one alga. Top expenditures for post-invasion investments went to eight insects [including Asian longhorned beetle], one mammal, and one bird.

Asian longhorned beetle

Just two of the costliest species were in both categories: insects red imported fire ant(Solenopsis invicta) and Mediterranean fruitfly (Ceratitis capitate). None of the species with the highest pre-invasion investment was among the top 10 costliest invaders in terms of damages. However, note the lack of data on fungi, chromists, and pathogens. (I wrote about this problem in an earlier blog.)

Discussion and Recommendations

Cuthbert et al. conclude that damage costs and post-invasion spending are probably growing substantially faster than pre-invasion investment. Therefore, they call for a stronger commitment to enhancing biosecurity and for more reliance on regional efforts rather than ones by individual countries. Their examples of opportunities come from Europe.

Drawing parallels to climate action, the authors also call for greater emphasis on during decision-making to act collectively and proactively to solve a growing global and inter-generational problem.

Cuthbert et al. focus many of their recommendations on improving reporting. One point I found particularly interesting: given the uneven and rapidly changing nature of invasive species data, they think it likely that future invasions could involve a new suite of geographic origins, pathways or vectors, taxonomic groups, and habitats. These could require different management approaches than those in use today.

As regards data and reporting, Cuthbert et al. recommend:

1) reducing bias in cost data by increasing funding for reporting of underreported taxa and regions;

2) addressing ambiguities in data by adopting a harmonized framework for reporting expenditures. For example, agriculture and public health officials refer to “pest species” without differentiating introduced from native species. (An earlier blog also discussed the challenge arising from these fields’ different purposes and cultures.)

3) urging colleagues to try harder to collect and integrate cost information, especially across sectors;

4) urging countries to report separately costs and expenditures associated with different categories, i.e., prevention separately from post-invasion management; damage separately from management efforts; and.

5) creating a formal repository for information about the efficacy of management expenditures.

While the InvaCost database is incomplete (a result of poor accounting by the countries, not lack of effort by the compilers!), analysis of these data points to some obvious ways to improve global efforts to contain bioinvasion. I hope countries will adjust their efforts based on these findings.

SOURCE

Cuthbert, R.N., C. Diagne, E.J. Hudgins, A. Turbelin, D.A. Ahmed, C. Albert, T.W. Bodey, E. Briski, F. Essl, P. J. Haubrock, R.E. Gozlan, N. Kirichenko, M. Kourantidou, A.M. Kramer, F. Courchamp. 2022. Bioinvasion costs reveal insufficient proactive management worldwide. Science of The Total Environment Volume 819, 1 May 2022, 153404

Seebens, H. S. Bacher, T.M. Blackburn, C. Capinha, W. Dawson, S. Dullinger, P. Genovesi, P.E. Hulme, M.van Kleunen, I. Kühn, J.M. Jeschke, B. Lenzner, A.M. Liebhold, Z. Pattison, J. Perg, P. Pyšek, M. Winter, F. Essl. 2021. Projecting the continental accumulation of alien species through to 2050. Glob Change Biol. 2021;27:970-982.

Williams, G.M., M.D. Ginzel, Z. Ma, D.C. Adams, F.T. Campbell, G.M. Lovett, M. Belén Pildain, K.F. Raffa, K.J.K. Gandhi, A. Santini, R.A. Sniezko, M.J. Wingfield, and P. Bonello 2022. The Global Forest Health Crisis: A Public Good Social Dilemma in Need of International Collective Action. submitted

Posted by Faith Campbell

Global Loss of Floristic Uniqueness

Hakalau Forest, Hawai“i; nearly 90% of Hawaiian flora is unique to the Islands

A recent article by Yang et al. 2021 (full citation at the end of this blog) seeks to determine the extent to which introduced plants reduce the uniqueness of regional floras. They analyzed data from 658 regions covering about 65.7% of the Earth’s ice-free land surface and about 62.3% of the planet’s known plant species.

They found strong homogenization of plant species’ taxonomic and phylogenetic diversity results from introductions of plant species to ecosystems beyond their native range. Homogenization caused by regional extinctions of native floral species occurs much less frequently.

There are two aspects of a region’s floral uniqueness. One is the number of species that it shares with other regions. This is taxonomic uniqueness. The other is the distinctiveness of the evolutionary history of the region. When several species are endemic to a region’s flora, and lack close relatives in other regions, that equals phylogenetic uniqueness.

The effect of a species introduction differs depending on which of these aspects one focuses on. Thus, naturalization of a species closely related to native species (e.g., a congeneric species) will have less impact on the phylogenetic floristic uniqueness of the region than naturalization by a distantly related species. Taxonomic uniqueness, however, will be affected to the same degree, irrespective of the phylogenetic distance between the naturalized and native species.

Yang et al. found strong homogenization of plant diversity. They found that species introductions increased the taxonomic similarity in 90.7% of all regional pairs and phylogenetic similarity in 77.2% of all region pairs. Most homogenization results from introductions of plant species to ecosystems beyond their native range. Homogenization caused by regional extinctions of native floral species occurs much less frequently.

This loss of regional biotic uniqueness or distinctiveness changes biotic interactions and species assemblages. These, in turn, have ecological and evolutionary consequences at larger scales and higher levels.

The degree of homogenization between regions’ floras depends on three factors:

1) The distance between the donor and recipient regions. Since nearby regions share more species, an introduction from a more distant origin is more likely to be a novel species and so contribute to homogenization of “donor” and “receiving” floras.

2) Climatic similarity, especially temperature. A plant species introduced from a climatically similar but geographically distant place is more likely to establish than a species from a different climatic zone. As a result, the recipient area’s flora is changed to more closely resemble the flora of the donor region with which it shares climatic conditions – regardless of the distance between them.

3) The level of exchange of goods and people between two regions. The higher the rate of exchange between two regions, the greater the chance that a species will be introduced and become established. Yang et al. used the existence of current or past administrative relationships (e.g., colonial relationship) between two regions as a proxy for intensity of trade and transport between donor and recipient regions. They found that floras of regions with current or past administrative links have taxonomically become more similar to each other than the floras of regions with no such links.

flora of the Cape Floral Kingdom – South Africa; photo from Michael Wingfield

Establishment of introduced species can increase floristic similarity of the donor and recipient regions (= floristic homogenization) when the species is native to one of the two regions and naturalizes in the other, or when it is not native to both regions and naturalizes in both. On the other hand, a species introduction can decrease the floristic similarity of the two regions (i.e., enhance floristic differentiation) when the species is not native to both regions but naturalized in only one.

Homogenization hotspots differed slightly depending on whether one focused on taxonomic or phylogenetic aspects.

The regions with the greatest average increase in taxonomic similarity with other regions due to naturalized alien species were New Zealand, portions of Australia, and many oceanic islands. The Australasian situation probably reflects its long biogeographic isolation from other parts of the globe and its highly unique native flora. As a result, nearly all non-native plants introduced to Australasia strongly increase levels of its floristic similarity to the rest of the world. Oceanic islands have species-poor floras with large proportions of unique endemics. They have also received high numbers of naturalized alien plants.

Hotspots of phylogenetic homogenization on continents are the same as those for taxonomic homogenization, but this is not true for islands. Yang et al. think this is because islands’ native floras were established by natural colonization from nearby continental floras so – despite subsequent speciation – they retain their phylogenetic relationship to the donor areas’ floras.

Yang et al. concede that they lacked high-quality data on native and naturalized alien species lists for a third of Earth’s ice-free terrestrial surface, especially Africa, Eastern Europe, and tropical Asia. They believe, however, that data from these regions are unlikely to change the overall finding. (Scientists are beginning to compile lists of forest pests in Africa). link to blog

Yang et al. note that introduction and naturalization of alien species are likely to increase in the future, thusaccelerating floristic homogenization. The ecological, evolutionary and socioeconomic consequences are largely unknown.They call for stronger biosecurity regulations of trade and transport and other measures to protect native vegetation.

SOURCE

Yang, Q., P. Weigelt, T.S. Fristoe, Z. Zhang, H. Kreft, A. Stein, H. Seebens, W. Dawson, F. Essl, C. König, B. Lenzner, J. Pergl, R. Pouteau, P. Pyšek, M. Winter, A.L. Ebel, N. Fuentes, E.L.H. Giehl, J. Kartesz, P. Krestov, T. Kukk, M. Nishino, A. Kupriyanov, J.L. Villaseñor, J.J. Wieringa, A. Zeddam, E. Zykova and M. van Kleunen. 2021. The global loss of floristic uniqueness. NATURE COMMUNICATIONS (2021) 12:7290. https://doi.org/10.1038/s41467-021-27603-y

Posted by Faith Campbell

Forest Pest Threat to Africa

Eucalyptus plantation in Kwa-Zulu-Natal, South Africa; Kwa-Zulu-Natal Dept. of Transportation

Graziosi et al. (full citation at the end of the blog) point out that trees are crucial for Africa’s future. Eight hundred of the 4,500–6,000 indigenous tree species provide significant food. As elsewhere, trees provide wood and other extractive resources essential for economic growth. They also support biodiversity and mitigate current and impending climatic variations. Africa– especially the Sub-Saharan countries – is already considered highly vulnerable to climate change.

According to Graziosi et al., the cumulative economic impact of all invasive species in Africa is expected to exceed $1.2 billion per year. The total invasion cost as a proportion of GDP for many African countries is among the highest in the world. This raises the stakes for developing locally appropriate management strategies across the continent.

Responding effectively to this threat is hampered by gaps in data as well as some countries’ limited capacity for biosecurity. Graziosi et al. say that improved knowledge of taxonomy, distribution, and damage caused by these organisms is essential. Such knoledge will be crucial to develop continent-wide strategies to manage this emergency and to enhance capacity for country-level interventions.

Native and alien pests. Indigenous and plantation trees

Africa’s trees and their services are threatened by both native pests and accelerating introductions of pests and diseases from elsewhere. Long-established and new invaders increasingly affect planted forests of exotic eucalypts, pines, and Australian acacias, as well as important indigenous trees. Graziosi et al. note that the U.N. Food and Agriculture Organization (FAO) in an annex to a report issued in 2009 recorded about100 species of forest pests affecting trees in planted and natural forests across Africa. Half are native insects and pathogens, a third are alien; about 15% are of unknown origin. Considering all pests, broadleaf trees (predominantly native) are most affected.

The result is damage from the local – e.g., to rural livelihoods – to the continental – e.g., to economic development and biological diversity across Africa. Moreover, pests exacerbate widespread loss of forest cover. Overall, African forests are shrinking at the rate of almost 0.5% annually. This deforestation is affecting particularly natural forests; planted forests are actually growing 1.3% annually.

Exotic plantation trees face severe threats. More than 47 native and 19 non-indigenous defoliators, sap-feeders, wood- and shoot-borers attack plantations of Acacia spp., Eucalyptus spp., Pinus spp., and teak (Tectona grandis). About 90% of pathogens of plantation forestry are either non-indigenous or of uncertain origin. Eucalyptus alone are severely damaged by 15 species of pathogens. These organisms are listed in Tables 1 and 2.

Numerous native insect species, known as pests of indigenous trees, have reportedly widened their host range and now damage exotic trees too. Some introduced insects appear to pose significant threats to native tree species. One example is the Cypress aphid Cinara cupressi, which is attacking both exotic cypress plantations and the native African cedar Juniperus procera. Some fungi in the family Botryosphaeriaceae are latent pathogens infecting a wide range of hosts including indigenous Acacia. Dieback of large baobab trees was recently reported from southern Africa. While various microorganisms are associated with these symptoms, the specific cause is still uncertain.

A baobab tree in Limpopo region of South Africa; Wikimedia

The risk currently appears to be particularly high in South Africa. The country’s flora is highly diverse and has a high level of endemism. In fact, South Africa is home to the Earth’s smallest floral kingdom, the Cape Floral Kingdom. It is also the apparent hot spot for pest introductions from overseas (see below). Phytophthora cinnamomi is attacking native Proteaceae in South Africa. According to Graziosi et al., an “incredible diversity” of Phytophthora taxa is present, portending threats to additional plant species. Other pathogens are attacking native conifers in the Podocarpus genus, Ekebergia capensis (Meliaceae), and Syzygium trees.

*Protea repens* and fynbos vegetation near Table Mountain; photo by Mike Wingfield

There is a clear pattern to further spread: pests first introduced to South Africa often spread. Examples include several insects and pathogens on Eucalyptus and the wood-boring pest of pine Sirex noctilio. This pattern is explained by two main factors. South Africa has a high capacity to detect introduced species. Also, there is an active plantation forestry sector that imports propagules. This offers opportunities for contaminating organisms to be introduced simultaneously.

Furthermore, as Graziosi et al. note, determining the geographic origin of significant proportion of pathogens is extremely difficult – an issue I will discuss in a separate blog based on a publication by primarily South African scientists. Some non-indigenous pathogens have been on the African continent for a long time. The Armillaria root rot pathogen apparently was introduced to South Africa with potted plants from Europe in the 1600s! They note also that many non-indigenous pathogens are probably already established on the continent but not yet detected due to the organisms’ cryptic nature and lagging detection abilities.

The future of African forests

African countries expect economic growth with associated increased trade with countries off-continent. The probable result will be to accelerate the rate of species introductions and spread. However, as climate change worsens, managers will find it increasingly difficult both to predict introduced species’ impact and to implement management programs.

This led Graziosi et al. to call for urgent improvements in plant biosecurity across the continent. They advocate improved coordination at regional and international levels. The list of needed actions is a familiar one: development and application of improved diagnostic tools, updated plant exchange regulations, and revised trade policies.

Graziosi et al. also call for development of effective control and management options. They suggest biocontrol, innovative silviculture practices, and selection of resistant trees. The good news is that African countries have already initiated programs to conserve tree germplasm and domesticate indigenous species, including establishment of field gene banks of high-priority indigenous trees. I have previously praised South African efforts, specifically reports here and here.

Mudada, Mapope, and Ngezimana (2022) describe the risk from introduced species to agriculture and human well-being in southern Africa beyond forestry. The region is already ravaged by food insecurities and hidden hunger. It would be devastated if the global average of crop loss due to plant diseases (10-16%) occurs there. They say these losses can be avoided with improved biosecurity mechanisms focused primarily on pest exclusion and plant quarantine regulations.

SOURCES

Graziosi, I. M. Tembo, J. Kuate, A. Muchugi. 2020 Pests and diseases of trees in Africa: A growing continental emergency. Plants People Planet DOI: 10.1002/ppp3.31

Mudada, N. Mapope, N., and Ngezimana, W. 2022 – The threat of transboundary plant pathogens to agricultural trade in Southern Africa: a perspective on Zimbabwe’s plant biosecurity – A review. Plant Pathology & Quarantine 12(1), 1–33, Doi 10.5943/ppq/12/1/1

Posted by Faith Campbell

For a detailed discussion of the policies and practices that have allowed these pests to enter the United States and spread – and that do not promote effective restoration strategies – review the Fading Forests report at http://treeimprovement.utk.edu/FadingForests.htm

British & Irish Efforts to Prevent or Combat Pathogens

I often blog about the forest pest situation in the UK because its scientists provide lots of easily accessible information. This blog has new information on Britain and – I am pleased to add – on Ireland!

European ash trees alongside the Malham Cove path in Yorkshire; KA via geograph

UK Overview

British woodlands cover just 13% of total land area (just over one-third of the European average of 37%). Their value is increasingly recognized—especially their role in combating climate change through carbon sequestration, flood mitigation and urban cooling. Realization of these benefits is driving new policy to increase woodland cover. In 2019–2020, 13,700 ha of new woodland was created in the United Kingdom (Green et al. 2021). The U.K. government has pledged to plant 30,000 ha of broadleaf and coniferous woodland every year as part of its climate change mitigation strategy (Donald et al. 2021). One example, the ‘northern forest’ scheme, involves planting 50 million native trees over 25 years (Green et al. 2021).

Risks Associated with Conservation Plantings or Translocations

On-going conservation planting efforts plus these ambitious new plans prompted Donald et al. (2021) to assess risk that pathogens might be introduced into the environment as a result of putting native plants in natural habitats. The focus of their study is the planting of common juniper (Juniperus communis)in habitats throughout England, Scotland, and Wales.

Juniper killed by *Phytophthora austrocedri*; photo from British Forest Research

Juniper is one of three native conifers in the UK. It has been in decline for decades, which conservationists hope to reverse. Now, though, juniper populations are experiencing significant mortality from disease. In 2012, the causal agent was determined to be the non-native pathogen Phytophthora austrocedri. The presence of a single genotype in ~60 geographically separate locations across Scotland and England lends support to idea that the pathogen is being introduced to these sites through some human mechanism. Phytophthora austrocedri has not [yet] been detected in Northern Ireland.

British and European nurseries have contained many Phytophthora pathogens. Hence Donald et al. (2021) sought to determine whether the pathogen is being introduced through use of nursery stock in these well-intentioned plantings. (I have blogged about a similar problem in California restoration plantings.)

The authors found that 19% of P. austrocedri detections are within 2 km of a known planting. The more frequently junipers were planted at a site, and the more cuttings planted during each planting effort, the higher the likelihood that nearby junipers would be infested by P. austrocedri. They conclude that transplanting material is a significant risk pathway for the introduction of disease. The key factor appeared to be the origin of the material. A higher percentage of stock at sites with P. austrocedri outbreaks for which data were available had been raised in a central location by the organization doing the planting or obtained from commercial nurseries. No P. austrocedri was detected in Wales. There, unlike in Scotland or England, the majority of plants were sourced from a commercial nursery that only grew juniper collected from Welsh populations and did not trade with other retailers.

Planting juniper has risen rapidly since the mid-1990s. The highest percentage of planting events co-occurring with disease outbreaks were conducted in 2000–2009. It is likely that there is a time lag between planting and disease detectability. If so, the even larger planting effort since 2010 probably will produce many more P. austrocedri outbreaks that will become visible in the future. And that might not be the end. Planting guidelines have been revised based on pathogen detection. However, the entities doing the planting have not changed their approach, especially regarding site selection.

Donald et al. (2021) also found serious data gaps in these programs beyond the health of propagules. They found:

1) very incomplete knowledge of which organizations are doing the planting;

2) poor attention to traceability of source material; and

3) very little follow-up to check the success of planting projects.

The authors concluded that planting projects have had mixed success in restoring juniper populations. They called for changes in planting strategy to reduce the risks of pathogen introduction.

They also note that efforts to slow the spread of P. austrocedri – for which there is no treatment – are more expensive and less likely to succeed than measures aimed at ensuring that nurseries are free of Phytophthoras. California native plant nurseries have shown that nurseries can maintain Phytophthora-free stock.

Risk of Nursery-spread Pathogens & Willingness of UK Nurseries to Adopt BMPs

Great Britain has experienced an accelerating series of Phytophthora outbreaks and disease epidemics affecting British trees. Introductions detected just since early 2000s include P. ramorum, P. kernoviae, P. lateralis, P. austrocedri and P. pseudosyringae. In all the above cases, imported planting material either is confirmed or strongly implicated as the likely route of intro (Green et al. 2021).

To address this threat – and with massive planting projects proposed – in 2016 the British forest research entity initiated the multidisciplinary ”Phyto-threats” project. Its goal was to understand the drivers of rising Phytophthora infestations and opportunities for mitigating them. The project:

(i) examined Phytophthora distribution and diversity in different nursery management systems;

(ii) assessed the social and economic feasibility of a nursery accreditation programs to curb the risk; and

(iii) identified Phytophthora risks by modelling introduction, establishment and spread of species in relation to biological characteristics, environmental factors and trade flows.

The assessment of Phytophthora presence in nurseries involved collecting 3,624 water and root samples from 163 host genera growing in plant nurseries across the U.K. over a three-year period. Sampling was not random but targetted to facilities thought to harbor Phytophthora. About half of the samples tested positive. They identified 63 species of Phytophthora. Among the most commonly detected species are several that are considered pathogenic — P. cinnamomi, P. cryptogea/pseudocryptogea, P. syringae, P. cactorum, P. cambivora, P. plurivora and P. nicotianae. P. ramorum was found in 12 samples; P. lateralis and P. austrocedri were each found in 10 samples. Several Phytophthora species are potential new records for the U.K. (i.e., P. castanetorum, P. palmivora, P. pseudotsugae,P. tentaculata,P. terminalis, P. uliginosa).

They also saw evidence for Phytophthora root infections in newly arrived plants imported from the European Union.

Their finding raised question about whether Phytophthora can be transported in peat-free potting media, that is, coconut fiber or coir.

The widespread presence and the diversity of Phytophthora found in nurseries was linked to high-risk management practices. These included: careless disposal of culled plants, the near presence of trees along nursery boundaries, and, especially, open water sources. [These factors are essentially identical to infection-facilitating factors found by researchers in California, Oregon, and Washington State. See advisory issued by Oregon State University Extension.]

The project also assessed the feasibility of nursery accreditation programs. The authors consulted widely with nursery owners and customers and conducted a cost-benefit analysis. Regarding nursery practices, owners claimed they were already addressing issues related to water storage in enclosed tanks, clean/covered storage of growing media, installation of drains or free-draining gravel beds, raised benches, and tool disinfestation stations. Therefore the new analysis focused on seven other topics: water testing for pathogens; water treatment s; quarantine holding areas for imported plants; composting or incineration of culled plants; boot and vehicle washing stations; and purchase from only trusted or accredited UK suppliers.

The study found that nurseries would support an accreditation program. However, their support required that costs not be “prohibitive”, actions required not be “unreasonable”, the scheme provide a safety net; and that measures exist to deter non-compliance. Nursery staff wanted to see evidence of consumer demand – a willingness to drive farther to buy “clean” plants, or to pay higher prices for them. The cost-benefit analysis reached a worrying conclusion: nurseries would benefit financially from introducing best practices only when the program would prevent introduction of a wider range of pests and pathogens, not only Phytophthoras. Green et al. (2021) note that the overall net benefit to society from nurseries adopting best practices would be much more substantial. That is, healthy trees are important in meeting carbon sequestration goals. They did not explore whether society should subsidize nurseries’ participation in BMP accreditation programs.

Ireland and Northern Ireland

The island of Ireland (Ireland and Northern Ireland) is thought to have fewer plant pests than other European countries due to its island status and because of its national and international phytosanitary regulations. O’Hanlon et al. (2022) do not mention another possible factor: the likelihood that import volumes to Ireland were probably much lower until the recent vitalization of the Republic’s economy.

O’Hanlon et al. (2022) sought to establish baseline information so scientists can track changes as trade increases and the climate changes. Their search of the literature and unpublished sources identified 396 forest pests on the island, including 11 bacteria, 20 oomycetes, 150 fungi and 215 arthropods. They believe these figures are all probably underestimates. At least 44 of the pests or pathogens are probably non-native to Ireland. (Determining original ranges is difficult, especially for pathogens.)

The Republic of Ireland is one of the least forested countries in Europe. Forests cover ~ 11% of the land area. In Northern Ireland, it is even less: ~ 8%. These forests are predominantly plantations of exotic species. In the Republic, Picea sitchensis makes up 51% of the forest area, Pinus contorta another 10%. Other exotic species planted are Picea abies (4%) and Larix kaempferi. In Northern Ireland, ~ 62% of the forest area is composed of conifer mixtures. Planting of P. sitchensis has accelerated recently, probably as a result of removal of ash and larch because of their vulnerability to pests already established on the island.

Sitka spruce plantation in U.K. Adam Ward, Geograph.org.uk

O’Hanlon et al. (2022) note the great vulnerability of these monocultures to pests. They found 51 pests native to Ireland that are associated with non-indigenous tree genera. They are also concerned about pests introduced from other parts of Europe. For example, green spruce aphid (Elatobium abietinum, native to Central and Eastern Europe) is already attacking Sitka spruce. A second pest of spruce, Ips typographus, which is native to much of Europe but not the British/Irish isles, is not yet established on the island. Northern Ireland imports bark and wood from Europe for processing. Ips typographus has been associated with at least one such shipment.

Non-native forest pests and pathogens also threaten tree species native to Ireland. These include:

Dutch elm disease caused by fungi from the genus Ophiostoma vectored by bark beetles of the genus Scolytus. The second outbreak, caused by the more aggressive pathogen 0. novo-ulmi, was detected in Britain in 1965 and in Ireland in 1977. It caused considerable mortality of elms in Northern Ireland throughout 1970s.

Phytophthora ramorum was recognized as a threat to forests in Europe only in 2010, when extensive mortality of Japanese larch was detected in Britain. The Republic of Ireland has only the EU1 lineage of the species. Northern Ireland has both the EU1 and EU2 lineages – the former only in nurseries.

Phytophthora disease of alder (caused by several Phytophthora species) was confirmed in Ireland in 2001. However, symptoms of the disease were noted as far back as 1995. It is likely that there are many other Phytophthora species present but not yet recorded.

Ash dieback disease (causal agent Hymenoscyphus fraxineus) on European ash (Fraxinus excelsior) has spread across Europe from Poland beginning in the 1990s. It was confirmed on the Irish island in 2012. Authorities made significant attempts to eradicate the disease, but were not successful. It is now recorded in every county in both Northern Ireland and Ireland. Damage to the economy, environment, and society are expected to be large. The Irish government had helped plant more than 13,000 ha of ash between 1992 and 2012. An estimated 2.9 million ash trees are in Northern Irish hedgerows. British scientists say more than 1,000 fauna species are associated with ash trees.

A second pest on ash — ash sawfly (Tomostethus nigritus) — was detected in Northern Ireland in 2016; it has defoliated hundreds of trees in Belfast.

In recent years, forest pest incursions have increased at a relatively steady rate, comparable to other countries, including Britain. In the 1970s, 26 species were reported; in the 1980s, 27; in the 1990s, 16; in the 2000s, 37; between 2010 and 2017, 28. See the graph in Fig. 2

There is a strong link between pest and pathogen findings in Britain and Ireland. O’Hanlon et al. (2021) list 16 insects and pathogens detected in Britain after 1960 which were later detected in Ireland. The list includes H. fraxineus, 0. novo-ulmi, Phytophthora ramorum, and Phytophthora lateralis. The average delay was 10 years. The authors note that the two islands share similar ecological conditions and hosts, are nearby, plus there is substantial travel and exchange of goods between them. For example, in 2018 an estimated 30,000 metric tonnes of conifer roundwood was sent from Scotland to Northern Ireland for processing.

There are very limited physical checks on plants or plant products moving between Ireland and Northern Ireland. The exception is conifer wood that is not bark-free. European Union regulations require that such shipments be accompanied by a plant passport that certifies that the wood has been inspected by a professional operator authorized by the NPPO of the exporting country. What rules will apply now, after BREXIT, remains unclear. Because of concerns about re-igniting sectarian conflict, most political figures want the border on the island to be almost invisible.

The Europhyt database for the period February 2006 – November 2016 documented interception of numerous high-risk pests at the British and Irish borders, including Anoplophora chinensis and A. glabripennis; I. typographus; Monochamus alternatus; H. fraxineus; and P. ramorum O’Hanlon et al. (2021). believe many more go undetected. O’Hanlon et al. (2021) report specifically on detections on commodities from China, especially on wood packaging. One detection on imported plants of interest to me is that of Discula destructiva (dogwood anthracnose). The article does not mention the origin of the shipment. The native British dogwood, Cornus sanguinea, would presumably be vulnerable to this Asian fungus, which has already caused widespread mortality of woodland dogwoods in North America.

*Cornus sanguinea*; photo by Hans Hillewaert

In addition to reviewing the current situation, O’Hanlon et al. (2021) note pertinent facts about current policy and future science. First, while the two political units on the island have a history of plant pathology expertise, there has recently been a reduction in the number of practicing forest pathologists, mycologists and entomologists. (I and others have complained about the same deterioration in expertise in the United States.)

Second, they describe the years of delay before official recognition that the pathogen Gremmeniella abietina was present in Northern Ireland. This delay resulted from officials refused to accept data from molecular detection tools.

O’Hanlon et al. (2021) add their voice to others criticizing the international phytosanitary system (they cite six major publications: Brasier 2008; Liebhold el. al. 2012; Santini et al. 2012; Eschen et al. 2015; Jung et al. 2016; Meurisse et al. 2019). The failures are (i) visual inspections can miss asymptomatic infections, (ii) limited resources mean only a small proportion of commodities can be inspected, (iii) allowing the use of fungicides masks disease symptoms on plants, (iv) list-based regulations don’t address undescribed organisms and (v) countries vary in how aggressively they carry out the required phytosanitary procedures. O’Hanlon et al. (2021) conclude that “Until these issues are addressed it is likely further increases in the numbers of non-native pests and pathogens of trees will increase.”

The authors note that Eschen et al. (2018) suggested that risk analysis should focus on the commodity (commodity risk assessment) rather than on an individual pest. I have made a similar suggestion, although less clearly worded.

Finally, O’Hanlon et al. (2021) note that climate change is expected to increase the island’s vulnerability to tree-killing pests and pathogens due to fewer frost days, more rain in winter, increased chance of drought in summer, increased average annual temperatures, and more frequent weather extremes. These changes are likely to affect the amount of damage caused by both native and introduced pests organisms. Range shifts in both pests and pathogens and their natural enemies; physiological or behavioral responses in the pests; phenological changes in the hosts; and increased stress on the trees will combine to affect damage.

SOURCES

Donald, F.; Purse, B.V.; Green, S. 2021. Investigating the Role of Restoration Plantings in Introducing Disease—A Case Study Using Phytophthora [UK] Forests 2021, 12, 764

Green, S., D.E.L. Cooke, M. Dunn, L. Barwell, B. Purse, D.S. Chapman, G. Valatin, A. Schlenzig, J. Barbrook, T. Pettitt, C. Price, A. Pérez-Sierra, D. Frederickson-Matika, L. Pritchard, P. Thorpe, P.J.A. Cock, E. Randall, B. Keillor and M. Marzano. 2021. PHYTO-THREATS: Addressing Threats to UK Forests and Woodlands from Phytophthora; Identifying Risks of Spread in Trade and Methods for Mitigation. Forests 2021, 12, 1617 https://doi.org/10.3390/f12121617ý

O’Hanlon, R., Ryan, C., Choiseul, J., Murchie, A.K. and Williams, C. D. 2021 Catalogue of P&P of trees on the island of Ireland. Biology and Enviro

Proceedings of the Royal Irish Academy 2021. Vol. 121, No. 1.12-45 DOI: 10.3318/ BIOE.2021.02

Posted by Faith Campbell

“Global Tree Assessment”: #s at Risk, Threats, & Carbon Sequestration Planting

Kew Gardens U.K., home to Botanic Gardens Conservation International; Wikipedia

A massive international effort has completed a “Global Tree Assessment: State of Earth’s Trees”. This is the result of five years’ effort; it aims at a comprehensive assessment of the conservation status of all the Earth’s trees. As a result of their work, the authors issue a call to action and include specific recommendations.

The leads were the Botanic Gardens Conservation International (BGCI) and International Union for Conservation of Nature’s (IUCN) Species Survival Commission (SSC) Global Tree Specialist Group. They were assisted by about 60 cooperating institutions and more than 500 individual experts. The Morton Arboretum was a major U.S. contributor. Here, my focus is on the global assessment. An accompanying blog contains my analysis of reports on the Morton Arboretum report for the U.S.

The Global Tree Assessment is the largest initiative in the history of the IUCN Red List process. (This process is described in Box 3 of the report, on p. 12; and on p. 40.) As of the end of 2020, IUCN Red List assessments evaluated 28,463 tree species, representing half of all known tree species. Organizers hope to complete comprehensive conservation assessments of all tree species for inclusion on the IUCN Red List by 2023. Other sources utilized included draft Red List profiles and national-level assessments of those species that are found in only one country.

SUMMARY OF FINDINGS

Using these sources, the Global Tree Assessment evaluated 58,497 tree species worldwide. The study determined that 30% are threatened with extinction. This number could change significantly if a large proportion of the 7,700 species (13.2%) recorded as “Data Deficient” turn out to be at risk. At least 142 species are recorded as already extinct in the wild. Two-fifths (41.5%) are considered to be not at risk. Detailed species’ evaluations are provided at GlobalTreeSearch or GlobalTree Portal.

Brazilian forest converted to cattle pasture

The principal threats to trees globally are forest clearance and other forms of habitat loss (at least 65% of species) and direct exploitation for timber and other products (27% or more). The spread of non-native pests is said to affect 5% of the species. Climate change is having a measurable impact on 4% of the species and is expected to increase. (The situation in the United States differs significantly. Overexploitation plays almost no role and on-going habitat loss is important for only a few of the at-risk species.)

The authors decry the lack of attention, historically, to tree endangerment given trees’ ecological, cultural and economic importance. They hope that increased attention to the biodiversity crisis — an estimated 1 million animal and plant species threatened with extinction — and trees’ importance as carbon sinks will lead to increased conservation of trees and forests. They warn, however, that tree-planting programs must put the right species in the right place, including utilizing species that are under threat. In other words, tree planting practices need to change. They note that a community of botanists and conservationists is ready to assist.

Centers of tree species diversity – and of species under threat – are in Central and South America, followed by the other tropical regions of Southeast Asia and Africa. Fifty-eight percent of tree species are single country endemics. The highest proportion of endemism is found in New Zealand, Madagascar and New Caledonia. The region with the highest proportion of native tree species under threat is tropical Africa, especially Madagascar. The highest numbers of species “Not Evaluated” or “Data Deficient” are in IndoMalaya (tropical Asia) and Oceania. In those regions, about a third of species fall in one of those categories.

The assessment authors fear ecosystem collapse caused by major, large-scale disturbance events. Examples are recent unprecedented fires in California, southern Australia, Indonesia, and the Amazon (although they don’t mention Siberia). They also note mass mortality events over large areas of forest caused by other factors, including drought and heat stress and the increased incidence of pests. These events have led to a worrying decline of dominant tree species currently evaluated as “Least Concern.” Citing a 2010 report, they list as examples spruce in Alaska, lodgepole pine in British Columbia, aspen in Saskatchewan and Alberta, and Colorado pinon pine (Pinus edulis) in the American southwest.

The authors emphasize the importance of preventing extinction of monotypic tree families. Such events would represent a disproportionate loss of unique evolutionary history, biological diversity, and potential for future evolution. Of the 257 plant families that include trees, 12 are monotypic. They are scattered around the tropics and former Gondwanaland; none is found in the Neo- or Paleoarctic regions. While extinctions to date have rarely affected plants above the rank of genus, the global assessment authors worry that the on-going sixth extinction wave might result in extinctions at the genus or family level.

In this context, the assessment made a particular effort to evaluate the status of species representing the survival of Gondwanian Rainforest lineages. They found that 29% of these tree species are threatened with extinction. Two case studies focus on Australia. They mention habitat conversion but not two non-native pathogens widespread in Australia, Phytophthora cinnamomi and Austropuccinia psidii.

formerly common, now endangered, Australian tree *Rhodamnia rubescens*, infected by *Austropuccinia psidii*; photo courtesy of Flickr

The proportion of total tree diversity designated as threatened is highest on island nations, e.g., 69% of the trees on St. Helena, 59% of the trees on Madagascar, 57% of the trees on Mauritius. Hawai`i is not treated separately from the United States as a whole. According to Megan Barstow of BGCI (pers. comm.), the just updated IUCN Red List includes 214 threatened tree species in Hawai`i.

[For the U.S. overall, the IUCN reports 1,424 tree species, of which 342 (24%) are considered threatened. In the companion U.S. assessment, the Morton Arboretum and collaborators found that 11% of 841 continental U.S. tree species are threatened.]

MAIN THREATS TO TREES

Habitat loss

Over the past 300 years, global forest area has decreased by about 40%. Conversion of land for crops and pasture continues to threaten more tree species than any other known threat. Additional losses are caused by conversion for urban and industrial development and transport corridors, and by changes in fire regimes. In total, these factors cumulatively threaten 78% of all tree species, 84% if one includes conversion to wood plantations.

Caribbean mahogany (*Swietenia mahogani*); photo by Miguel Vieria

Forest Exploitation

Exploitation, especially for timber, is the second greatest threat globally, affecting 27% of tree species (more than 7,400 tree species). The report focuses on centuries of harvest of valuable tropical timbers and exploitation for fuelwood, with an emphasis on Madagascar, where nearly half of all tree species (117 out of 244 tree species) are threatened.

Pests and diseases

Tree species are impacted by a wide range of pests and diseases that are spread by natural and artificial causes. Invasive and other problematic species are recorded as threats for 1,356 tree species (5%) recorded on the IUCN Red List. This figure might be low because some of the information is outdated (see my discussion of American beech in the companion blog about the North American report, here.) Also, climate change is altering the survival opportunities for many pests and diseases in new environments. The example given is the ash genus (Fraxinus), under attack by not only the emerald ash borer in North America and now Russia and Eastern Europe but also the disease Ash Dieback across Europe. The report refers readers to the International Plant Sentinel Network for early warning system of new and emerging pest and pathogen risks, as well as help in coordinating responses.

black ash (*Fraxinus nigra*) swamp; Flickr

Climate Change

Climate change is impacting all forest ecosystems and is emerging as a significant recorded threat to individual tree species. In the IUCN Red List assessments, climate change and severe weather is recorded as a threat in 1,080 (4%) cases. Trees of coastal, boreal and montane ecosystems are disproportionately impacted. The authors note that the actual impact of climate change is probably more widespread, as it is also impacting fire regimes and the survival, spread, and virulence of pests.

CURRENT CONSERVATION EFFORTS

In Protected areas

Currently, 15.4% of the global terrestrial surface has formal protection status. The IUCN study authors recognize in situ conservation of trees through protection of existing natural habitats as the best method for conserving tree diversity. It is therefore encouraging that at least 64% of all tree species are included in at least one protected area. However, representation is higher for species that are not threatened – 85% are represented in a conservation area while only 56% of threatened trees species are. Nor does the report assess the effectiveness of protection afforded by the various in situ sites. The authors express hope that the parallel IUCN Red List of Ecosystems will contribute to understanding of the efficacy of conservation efforts targetting forests.

The Global Trees Campaign is a joint initiative of Fauna & Flora International (FFI) and BGCI. Since 1999 the campaign has worked to conserve more than 400 threatened tree species in more than 50 countries. The current focus is on six priority taxa = Acer, Dipterocarps, Magnolia, Nothofagus, Oak, and Rhododendron.

Rhododendron in Cook Forest State Park, PA; photo by F.T. Campbell

In Botanic gardens and seed banks

Especially for species under threat, conservation outside their native habitat – ex situ conservation – is an essential additional component. Currently 30% of tree species are recorded as present in at least one botanic garden or seed bank. Again, representation is higher for species that are not threatened – 45% are represented compared to only 21% of threatened tree species. For 41 species, ex situ conservation provides the only hope of survival, since they are extinct in the wild.

AN URGENT CALL FOR ACTION

The authors and collaborators who prepared the Global Tree Assessment hope that this report will help prompt action and better coordination of priorities and resources to better ensure that all tree species are supported by in situ conservation sites and by appropriate management plans. They state several times the importance of restoration plantings relying on native species. The purpose of plantings needs to include conservation of biological diversity, not just accumulation of carbon credits. The Ecological Restoration Alliance of Botanic Gardens (https://www.erabg.org/) is demonstrating that forest restoration can benefit biodiversity conservation. In many cases, propagation methods need to be developed. Also, projects must include aftercare and monitoring to ensure the survival of planted seedlings.

The IUCN assessment notes that ex situ conservation is an important backup. Education, capacity-building and awareness-raising are needed to equip, support, and empower local communities and other partners with the knowledge and skills to help conserve threatened trees.

Policy

The report say it does not address policy and legislation – a gap that fortunately is not quite true. The report both summarizes pertinent international agreements but also provides specific recommendations.

The international agreements that pertain to tree and forest conservation include:

Convention on Biological Diversity (CBD) and several specific programs: the Forestry Programme, Protected Area Programme and Sustainable Use Programme.
Global Strategy for Plant Conservation (GSPC), which is now developing post-2020 targets.
United Nations Framework Convention on Climate Change (UNFCCC) and countries’ implementing pledges to conserve carbon sinks, e.g., REDD+ (Reducing Emissions from Deforestation and Forest Degradation)
United Nations Strategic Plan for Forests 2017-2030
Global Plan of Action for the Conservation and Sustainable Use of Forest Genetic Resources
Convention on International Trade in Endangered Species, which currently protects 560 tree species, including 308 of the most threatened timbers

The report also mentions the voluntary New York Declaration on Forests, under which more than 200 entities – including governments, businesses, and Indigenous communities — have committed to eliminating deforestation from their supply chains. The supply chains touched on include those for major agricultural commodities, production of which is one of the greatest threat to trees.

SPECIFIC RECOMMENDATIONS

1. Strengthen tree conservation action globally through the formation of a new coalition that brings together existing resources and expertise, and applies lessons from the Global Trees Campaign to radically scale up tree conservation.

2. Use information in the GlobalTree Portal on the conservation status of individual tree species and current conservation action to plan additional action at local, national, and international levels, and for priority taxonomic groups. Build on the Portal by strengthening research on “Data Deficient” tree species, and collating additional information threatened species to avoid duplication of efforts and ensure conservation action is directed where it is needed most.

3. Ensure effective conservation of threatened trees within the protected area network by strengthening local knowledge, monitoring populations of threatened species and, where necessary, increasing enforcement of controls on illegal or non-sustainable harvesting of valuable species. Extend protected area coverage for threatened tree species and species assemblages that are currently not well-represented in protected areas.

4. Ensure that all globally threatened tree species are conserved in well-managed and genetically representative ex situ living and seed bank collections, with associated education and restoration programs.

5. Align work with the UN Decade on Ecosystem Restoration 2021–2030, engaging local communities, government forestry agencies, the business community, and other interested parties to ensure that the most appropriate tree species, including those that are threatened, are used in tree planting and restoration programs.

6. Improve data collection for national inventory and monitoring systems and use this information to reduce deforestation in areas of high tree diversity in association with REDD+ and Nationally Determined Contributions (NDCs).

7. Increase the availability of government, private and corporate funding for threatened tree species, and ensure that funding is directed to species and sites that are in greatest need of conservation.

SOURCE

Global Tree Assessment State of Earth’s Trees September 2021 Botanic Gardens Conservation International available here

Posted by Faith Campbell

The South African Report as a Model: U.S. Falls Short

Ailanthus – one of the invasive species shared by South Africa and the U.S.

A few years ago, I posted a blog in which I pointed to a report on South Africa’s response to bioinvasion as a model for the U.S. and other countries. South Africa has published its second report. This report outlines the country’s status as of December 2019 and trends since the first report (i.e. since December 2016). (I describe the report’s findings on South Africa’s invasive species situation in a companion blog.) Again, I find it a good model of how a country should report its invasive species status, efforts, and challenges. In comparison, many U.S. efforts comes up short.

U.S. Reports Need to Be More Comprehensive

The South African report provides a national perspective on all taxa. Various United States agencies have attempted something similar a few times. The report issued by the Office of Technology Assessment in 1993 summarized knowledge of introduced species and evaluated then-current management programs.

The 2018 report by the U.S. Geological Service focused on data: the authors concluded that 11,344 species had been introduced and described the situation in three regions – the “lower 48” states, Alaska, and Hawai`i. However, the USGS did not evaluate programs and policies. The new USDA Forest Service report (Poland et al. 2021) describes taxa and impacts of invasive species in forest and grassland biomes, including associated aquatic systems. Again, it does not evaluate the efficacy of programs and policies.

The biennial national reports required by the Executive Order establishing the National Invasive Species Council (NISC) are most similar to the South African ones in intent. However, none has been comprehensive. For example, the most recent, issued in 2018, strives to raise concern by stating that invasive species effect a wide range of ecosystem services that underpin human well-being and economic growth. Some emphasis is given to damage to infrastructure. The report then sets out priority actions in six areas: leadership and prioritization, coordination, raising awareness, removing barriers, assessing federal capacities, and fostering innovation. NISC also issued a report in 2016 – this one focused on improving early detection and rapid response. NISC posted a useful innovation – a “report card” updating progress on priority actions — in October 2018. It listed whether actions had been completed, were in progress, or were no longer applicable. However, the “report card” gave no explanation of the status of various actions; the most notable omissions concerned the actions dismissed as “not applicable”. Worse, no report cards have been posted since 2018. I doubt if those or any more comprehensive reports will be forthcoming. This reflects the increasing marginalization of NISC. The Council has never had sufficient power to coordinate agencies’ actions, and now barely survives.

U.S. Reports Need to Be More Candid

The authors of the South African report made an impressive commitment to honest evaluation of the country’s gaps, continuing problems, progress, and strengths. As in the first report, they are willing to note shortcomings, even of programs that enjoy broad political support (e.g., the Working for Water program).

It is not clear whether decision-makers have acted — or will act — on the report’s findings. That is true in many countries, including the United States. However, that is separate whether decision-makers have an honest appraisal on which to base action.

Assessment of South Africa’s Invasive Species Programs

Here is a summary of what the authors say about South Africa’s invasive species program. I want to state clearly that my intention is not to criticize South Africa’s efforts. No country has a perfect program, and South Africa faces many challenges. These have been exacerbated by COVD-19.

The report identifies the areas listed below as needing change or improvement.

1) Absence of a comprehensive policy on bioinvasion. Such a policy would provide a vision for what South Africa aspires to achieve, clarify the government’s position, guide decision-makers, and provide a basis for coordinating programs by all affected parties (e.g., including conservation and phytosanitary agencies).

2) As in the first report, the authors call for monitoring program outcomes (results) rather than inputs (money, staffing, etc.) or outputs (e.g., acres treated). The authors also say data must be available for scrutiny. In those cases when data are adequate for assessing programs’ efficacy, they indicate that the control effort is largely ineffective.

3) Inadequate data in several areas. The report notes progress in developing and applying transparent and science-based criteria to species categorization as invasive (as distinct from relying on expert opinion). However, this change is taking time to implement, and sometimes results in species receiving a different rating. [I agree with the report that data gaps undermine understanding of the extent and impacts of bioinvasion, domestic pathways of spread, justification of expenditures, assessment of various programs’ efficacy (individually or overall), priority setting, and identifying changes needed to overcome programs’ weaknesses. However, I think filling these data gaps might demand time and resources that could better be utilized to respond to invasions – even when those invasions are not fully understood.]

4) Funding of bioinvasion programs by the National Department of Forestry, Fisheries, and the Environment has been fairly constant over 2012–2019, but this is a decline in real terms. The figure of 1 billion ZAR does not include spending by other government departments, national and provincial conservation bodies, municipalities, non-governmental organizations, and the private sector. Authors of the report expect funding to decrease in the future because of competing needs.

While at least 237 invasive species are under some management (see Table 5.1), funding is heavily skewed – 45% of funding goes to management of one invasive plant (black wattle); 72% to management of 10 species.

5) Need for policies to address the threat emerging from rising trade with other African countries, especially considering the probable adoption of the proposed African Continental Free Trade Area. Under this agreement, imported goods will only be inspected for alien species at the first port of entry, and most African countries have limited inspection capacity. [European pathologists Brasier, Jung, and others have noted the same issue arising in Europe, where imported plants move freely around the European Union once approved for entry by one member state.]

The authors of the South African report say programs’ efficacy would be considerably improved if species and sites were prioritized, and species-specific management plans developed. They warn that, in the absence of planning and prioritization, there is a risk that funding could be diluted by targeting too many species, leading to ineffective control and a concomitant increase in impacts.

In South Africa, regulations, permits, and other measures aimed at regulating legal imports of listed species are increasingly effective. However, there is still insufficient capacity to prevent accidental or intentional illegal introductions of alien species. There is also more enforcement of regulations requiring landowners to control invasive species. Six criminal cases have been filed and – as of December 2019, one conviction (guilty plea) obtained. However, the data do not allow an assessment of the overall level of compliance.

The report found little discernable progress on the proportion of pathways that have formally approved management plans. Management is either absent or ineffective for 61% of pathways. There has been no action to manage the ballast water pathway. On the other hand, in some cases, other laws focus explicitly on pathways, e.g., agricultural produce is regulated under the Agricultural Pests Act of 1983.

During the period December 2016 – December 2019, the Plant Inspection Services tested more than 12,000 plant import samples for quarantine pests and made 62 interceptions. The report calls for more detailed information from the various government departments responsible for managing particular pathways (e.g., the phytosanitary service), and for an assessments of the quality of their interventions.

The number of non-native taxa with some form of management has grown by 40% since December 2016 – although – as I have already noted — spending is highly skewed to a few plant species. The number and extent of site-specific management plans has also increased, apparently largely due to a few large-scale plans developed by private landowners. However, few of these plans have been formally approved by some unspecified overseer.

Citing the strengths and weaknesses described above, the current (second) report downgraded its assessment of governmental programs from “substantial” to “partial”.

Comparison to U.S.

How does the United States measure up on the elements that need change or improvement? I know of no U.S. government report that is as blunt in assessing the efficacy of our programs –individually or as a whole.

Nevertheless, each of the five weaknesses identified for South Africa also exist in the United States:

Re: lack of a comprehensive policy, I think the U.S. also suffers this absence. This is regrettable since the National Invasive Species Council (NISC) was set up in 1999.
Re: monitoring outcomes to assess programs’ efficacy, I think U.S. agencies do seem to be more focused on collecting data on programs’ results – see the Forest Service’ budget justification. However, I think too often the data collected focus on inputs and outputs.
Re: data gaps, I think all countries – including the U.S. — lack data on important aspects of bioinvasion. I differ from the South African report, however, in arguing for funding research aimed at developing responses rather than monitoring to clarify the extent of a specific invasive species. Information that does not lead to action seems to me to be a luxury given the low level of funding.
Re: funding, I find that, despite the existence of NISC, it remains difficult to get an overall picture of U.S federal funding of invasive species programs. Indeed, the cross-cut budget was dropped in 2018 at the Administration’s request. I expect all agencies are under-funded; I have often said so as regards key USDA programs. As in South Africa, funding is skewed to a few species that I think should be lower in priority (e.g., gypsy moth).
Re: upgrading invasive species programs to counter free-trade policies, I think U.S. trade policies place too high a priority on promoting agricultural exports to the detriment of efforts to prevent forest pest introductions. This imbalance might be present with regard to other taxa and pathways. See Fading Forests II here.

South African and U.S. agencies also face the same over-arching issues. For example, the U.S. priority-setting process seems to be a “black box.” Several USFS scientists (Potter et al. 2019) spent considerable effort to develop a set of criteria for ranking action on tree species that are hosts of damaging introduced pests. Yet there is no evidence that this laudable project influenced priorities for USFS funding.

SOURCES

Poland, T.M., P. Patel-Weynand, D.M Finch, C.F. Miniat, D.C. Hayes, V.M Lopez, editors. 2021. Invasive Species in Forests and Rangelands of the United States. A Comprehensive Science Synthesis for the US Forest Sector. Springer

Potter, K.M., Escanferla, M.E., Jetton, R.M., Man, G., Crane, B.S. 2019. Prioritizing the conservation needs of United States tree species: Evaluating vulnerability to forest P&P threats, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/j.gecco.2019.e00622.

SANBI and CIB 2020. The status of bioinvasions and their management in South Africa in 2019. pp.71. South African National BD Institute, Kirstenbosch and DSI-NRF Centre of Excellence for Invasion Biology, Stellenbosch. http://dx.doi.org/10.5281/zenodo.3947613

Posted by Faith Campbell