Stress-Loving Plants and At-Risk Flora in Harpers Ferry

By Megan Nortrup, National Park Service 

Riversides scoured by constant flooding. Thin soils on top of rock beds. Some habitats are so stressful, only a few species have adapted to them and can survive. But in adapting to these tough conditions, these specialized plants (some are “edaphic” and are restricted to certain soil conditions) don’t compete well in the relatively cushy conditions found elsewhere. They are very few in number and paradoxically, some of these rugged plants are considered vulnerable.

A project to document vulnerable plants in some of these “extreme” places at Harpers Ferry (originally presented in the Fall 2019 issue of the National Park Service’s Natural Resources Quarterly newsletter) recently released a preliminary summary of their results.

A team from Frostburg State University led by Clara Thiel revisited spots where rare, threatened, and endangered plants had been recorded before, to see if the plants were still around and in what numbers, and to document conditions at each site. The vulnerable plants they sought have conservation rankings of S1 (critically imperiled), S2 (imperiled), or S3 (vulnerable). (Learn more about conservation rankings).

During their resurveys, they found:

• Thirty four of 56 previously documented S1-S3 species
• Ten additional S1-S3 species not previously documented in the park

Changes in Vulnerable Plants Follow Changes in Habitat Stability

The loss and change to populations of vulnerable plant species was primarily attributed to competition from invasive species, habitat loss, and changes in site maintenance or disturbance regimes. The Frostburg team recommended that sensitive habitats remain or become protected from the public, and that invasive species removal projects be prioritized.

In revisiting plant surveys done in the mid-1980s and late 1990s, this project offers the chance to look at vulnerable plants and the effects of:

• large-scale forest changes and canopy loss from spongy moth (Lymantria dispar) and emerald ash borer (Agrilus planipennis)
• management actions, inactions, or changes
• increased park visitation and access

Most urgently, researchers encouraged management of the large population of the highly invasive kudzu vine (Pueraria montana) growing along Route 340 that threatens the floodplain habitats of the Potoma Wayside.

Highlights from this project

• Current peregrine falcon closures along the Maryland Heights overlook area are likely to benefit existing populations of lobed spleenwort (Asplenium pinnatifidum) that were documented in 2012.
• The Virginia portion of the park preserves high-quality riparian and river scour habitat home to several state and regionally rare plant species.
• Several invasive species have become established in the park’s Virginia floodplains and pose threats to many vulnerable plants.
• High diversity areas in the West Virginia portion of the park should remain a top priority for maintenance and protection.
• Globally rare limestone cedar glade habitats have experienced extensive canopy closure in the absence of regular mowing or grazing that is stressing vulnerable sun-loving species.

Project Facilitation

This project was facilitated by the Chesapeake Watershed Cooperative Ecosystem Studies Unit (CHWA CESU). The CHWA CESU promotes stewardship and integrated ecosystem management of natural and cultural resources in the Chesapeake Watershed through collaborative research, technical assistance, and education. To do research with CHWA CESU, please contact Danny Filer at 301-689-7108.

The preceding article was originally published in the National Park Service’s Summer 2022 Natural Resources Quarterly newsletter.