The recent appearance of a study by National Park Service (NPS) scientists quantifying the threat posed by invasive plants prompted me to seek updates on this issue. In May 2018, I blogged about NPS’ Invasive Plant Program Strategic Plan, which was issued in 2016. At the time, I got the impression that the program was struggling to gain support from NPS leadership in Washington, as well as leaders of individual parks. Has the situation improved since then?
The recent study, by Kathryn Miller and colleagues, focuses on National parks in the East, from Virginia to Maine. (I provide a full reference at the end of this blog.) I look forward to a planned follow-up article that will try to clarify drivers of invasion.
The Miller study appears to have been undertaken to partially fulfill one of the goals of the NPS’ 2016 Invasive Plant Program Strategic Plan. One of the actions under Goal 1 in the Plan was to quantify the invasive plant threat, the effort needed to manage it, and then to communicate the gap between needs and available resources. Miller et al. have quantified the threat to National parks in one region (not the entire country). However, they have communicated the gap between effort and need in only the most general way.
Protecting the forests in eastern National parks is valuable from many perspectives. The forests in these parks are older and have higher stand-level tree diversity than surrounding unprotected forests. Protecting their long-term condition also corresponds to the National Park Service’s (NPS) stated mission, as established in its Organic Act.
The study relied on National Park Service Inventory and Monitoring Program data from 1,479 permanent forest plots covering 39 eastern NP units located from Virginia to Maine. The data were collected over 12 years, in three survey cycles (2007–2010, 2011–2014, and 2015–2018).
The authors note that in forest ecosystems, invasive plants can reduce native diversity, alter forest structure, suppress tree regeneration, alter nutrient cycling, and modify disturbance regimes. Some – the shrubs and vines – also threaten human health by promoting increases in tick populations and associated Lyme disease risks.
Unsurprisingly, the data showed invasive plants to be widespread, and increasing. In 80% of the park units, there was a significant increase in at least one trend measuring abundance. Any decrease in plant invaders tended to be in herbaceous or graminoid species; that decrease was often counterbalanced by an approximately equivalent increase in invasive shrubs or vines. In 35 of the park units, more than half of the plots had at least one invasive plant species when the 2015-2018 survey began. In 10 parks (a quarter of those surveyed), every plot had at least one.
The most widespread species is Japanese stiltgrass (Microstegium vimineum). It is present in more than 75% of all park units and 30% of all 1,400 plots. This dominance is true despite the fact that stiltgrass does not extend north of Roosevelt-Vanderbilt National Historic Site in New York state (41o N latitude). Stiltgrass is also the most aggressive invader.
The second most widespread invaders are a group of shrubs and vines, including most notably Japanese barberry (Berberis thunbergii), Japanese honeysuckle (Lonicera japonica), multiflora rose (Rosa multiflora), and wineberry (Rubus phoenicolasius). I note – although the articles does not – that several of these have been deliberately planted – either to “enhance” ecosystems (multiflora rose) or as ornamentals (barberry). [Lehan et al. 2013 (full reference at end of blog) found that 95% of 125 shrub species introduced to the U.S. were introduced deliberately.] I know of no examples of deliberate planting of Japanese stiltgrass.
The most frequently detected non-grass herbaceous species is garlic mustard (Alliaria petiolata), which was detected in 20% of plots. Garlic mustard is found throughout the study area (Virginia to Maine). Tree-of-heaven (Ailanthus altissima) is the most common invasive tree. It is found in only 9% of plots and does not grow north of Roosevelt-Vanderbilt NHS. Again, both were intentionally introduced – and not noted as such in the article.
Because they could not identify the source populations for each plot, the study could not directly measure rates of establishment and expansion. The data did allow tracking rough trends in each park.
Parks with the highest abundance tended to be near densely populated areas. However, this pattern was not universal. For example, Prince William Forest Park in the outer Virginia suburbs of the District of Columbia metro area was one of two of the least invaded park units.
(note the prevalence of beech – I fear for the arrival of beech leaf disease!)
Total invasives increased significantly in 21 of the 39 parks for at least one metric. In 10 parks (a quarter of all parks), total invasives increased significantly in two of the three metrics. Antietam National Battlefield experienced the steepest increases.
The authors note that invasive plants continue to establish and expand, even in already heavily invaded forests. Thus they found little evidence of saturation. This finding conflicts with invasion theory. They also found antagonistic interactions between invasive species to be common.
The authors said managers should prioritize efforts to control Japanese stiltgrass and the shrubs and vinesdue to their widespread occurrence, rapid expansion, ability to suppress tree regeneration and understory diversity, and – in the case of the shrubs and vines, link to ticks.
The authors noted the need to better understand the drivers and impacts of invasive plants in eastern forests. They mentioned the overabundance of white-tailed deer (Odocoileus virginianus), latitude, climate change, fragmentation and urbanization. I have urged them to include analysis of deliberate planting of various species on lands within the park units or nearby. They have said that they will do so in the planned follow-up article.
The authors propose that deferred management of natural resources receive attention and sustained commitment on par with the attention to deferred maintenance of the park units’ infrastructure. The maintenance backlog has been addressed through recent legislation: the Great America Outdoors Act which provided $6.5 billion over five years to address deferred maintenance projects in all 419 national park units. I believe that these projects will not address invasive species, which are managed under the “Natural Resources” budget account, not “Maintenance”. Some “Maintenance” projects probably will include control of invasive plants. A former Interior Department official has suggested that resource management activities might be funded under another section of the legislation, which provides $900 million under the Land and Water Conservation program. I hope this is true.
National Park Service’ Overall Invasive Plant Program Now
In response to the mandate in the John D. Dingell, Jr. Conservation, Management, and Recreation Act (Public Law 116-9), the Department of Interior has issued a department-wide invasive species strategy. Will issuance of the new strategy provide impetus to the NPS to seek funding to implement its 2016 invasive plant strategic plan? Will Congress provide funds for this purpose?
Finding out the current status of National Park Service took a little effort. The NPS’ website has “popular” information about the efforts of individual regional Invasive Plant Management Teams (see links at the end of this blog). These posts provide only the briefest overview of program achievements and do not compare those accomplishments to the goals in the 2016 plan.
However, Terri Hogan, Invasive Plant Program Manager in the Biological Resources Division, provided following information:
NPS leadership now supports the agency’s invasive plant effort. The national Invasive Plant Program (IPP) contributes to the annual Natural Resource Stewardship and Science Directorate (NRSS)’ Biological Resource Division (BRD) work plan. All is guided by the “Four Pillars to Guide Natural Resource Activities and Investments”, adopted in 2016.
It is not clear that invasive species have the highest priority under this regime. The four “pillars” are
- Holding the line – includes conserving biodiversity by removing invasive plants
- Managing amid Continuous Change – includes conducting risk assessment and taking other actions to contain future exotic species
- Leveraging for Conservation at Scale
- Enhancing Stewardship and Science Access and Engagement
Cooperation with owners of neighboring private lands has been enhanced by engagement of the Western Governors Association and state and local political leaders. Many parks participate in Partnerships for Invasive Species Management (PRISMs), CISMS, and Cooperative Weed Management areas (CWMAs). This collaboration has been strengthened by adoption of the John D. Dingell, Jr. Act (see above).
In practice, the focus appears to still be on the Invasive Plant Management Teams (IPMTs). There are now 17 teams. Fifteen are funded through the national office. One is funded by an individual park; one funded through a regional office. Annual reports have been published for FYs 2017 and 2018. The FY19 report has been held up but should be posted soon.
The reports provide brief description of the overall program and vignettes of particular activities. There are more detailed – but still anecdotal – reports for each of the teams. It is difficult to determine whether there has been overall progress. For example, the reported total infested acreage increased from 133,658 acres in FY17 to 301,195 acres in FY18. This presumably reflects more intense monitoring as well as a probable increase in real infections. (The infested acreage figures do not address intensity of invasion on these acres.) The teams cumulatively treated 8,937 acres in FY 2017; 8,331 acres in FY 2018. They carried out inventory and monitoring projects on 169,057 acres in FY17, 210,000 acres in FY18.
Since the Miller article concerns the region from Virginia to Maine, I checked the FY17 and FY 18 reports from the Invasive Plant Management Teams from the Mid-Atlantic, National Capital Area, and Northeastern regions. The Mid-Atlantic team emphasized work on wavyleaf basketgrass and meadows in parks established to protect cultural or historic sites. The National Capital Area team emphasized partnerships and success eradicating Giant Hogweed (Heracleum mantegazzianum) on private land neighboring Rock Creek Park. The Northeastern Team serves 25 parks; the report emphasized leveraging resources and testing efficacy of pre-emergent herbicide for control of Japanese stiltgrass. With this exception, the teams do not appear to be prioritizing the species recommended for action by the Miller study.
Brief, “popular” articles about the NPS’ invasive plant effort are available here
NPS 20 Years of Invasive Plant Management
20 Years of Action in 2020: Invasive Plant Management Teams
20th Years of Action – The NPS IPMT Program
SOURCES
Lehan, N.E., J.R. Murphy, L.P. Thornburn, and B.A. Bradley. 2013. Accidental Introductions are an Important Source of Invasive Plants in the Continental United States. American Journal of Botany 100(7): 1287–1293. 2013.
Miller, K. M., B. J. McGill, A. S. Weed, C. E. Seirup, J. A. Comiskey, E. R. Matthews, S. Perles, & J. Paul Schmit. 2020. Long-term trends indicate that invasive plants are pervasive and increasing in eastern national parks. Ecology. 00(00):e02239. 10.1002/eap.2239
Posted by Faith Campbell
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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
Japanese stiltgrass and Tree-of -heaven is a problem in Columbia County, NY. In the article above it was mentioned that neither grow north of Roosevelt-Vanderbilt National Historic Site in New York state (41o N latitude). This incorrect and the list of parks where these can be found is growing every year.
The article’s author, Elizabeth Matthews, reminds us that the report referred to detections of various plant species in National park units. Data do not reflect the species’ range without consideration of land ownership. In the case of Japanese stiltgrass, the range includes southern New York. [See Appendix S1 in the article/] I added the latitude in an effort to clarify where the Park is for readers not familiar with New York State. I probably caused unnecessary confusion!