This is a guest post by Bert Harris from the Clifton Institute
Grassland in Prince William County, VA with Wavyleaf Aster and Gray Goldenrod. Photo by Bert Harris, Clifton Institute.
Grasslands of the northern Virginia Piedmont are little studied plant communities that are home to several declining bird and insect species. In the summer of 2020, researchers from the Clifton Institute, Virginia Tech, the Center for Urban Habitats, and Virginia Working Landscapes, studied the flora of 37 natural grasslands in five counties (Fauquier, Culpeper, Prince William, Fairfax, and Rappahannock). We did this to: (1) learn which species of plants are found in natural grasslands in the northern Virginia Piedmont, (2) identify threats and conservation solutions for these habitats, and (3) design seed mixes for use in wildflower meadow plantings and grassland restoration projects in our area.
We sampled grasslands with a 50 x 2-meter plot from May to September 2020, with the goal of sampling each site early and late in the season. We found 433 species of plants, 84% of which were native to Virginia. We found one globally rare plant (Torrey’s Mountain-mint Pycnanthemum torreyi) and three state-rare species (Stiff Goldenrod Solidago rigida, American Bluehearts Buchnera americana, and Purple Milkweed Asclepias purpurascens) in our survey sites. We also encountered two uncommon plants, Nodding Ladies’-tresses (Spiranthes ochroleuca) and White Heath Aster (Symphyotrichum ericoides), that were considered to be rare in the state until recently. We documented at least 16 new county records, in a region that has received substantial attention from botanists.
Six of our study sites were extraordinarily diverse compared to other vegetation surveys that have been done in Virginia (see table below).
The most diverse meadows were found on relatively basic, clay-hardpan soils over diabase bedrock. High-quality meadows were also found on more acidic soils over sandstone and greenstone (metabasalt). The highest quality grasslands were found in powerline clearings that are mowed annually. Constant grazing and frequent hay cutting seem to be incompatible with species rich natural grasslands in the northern Piedmont.
Unfortunately, three populations of rare plants in powerline clearings were accidentally sprayed with herbicide by power companies during our study. Several sites are also threatened by invasion of plants from Asia, Europe, and the mid-western US. Invasions of Chinese Bush-clover (Lespedeza cuneata), Spotted Knapweed (Centaurea stroebe), Joint-head Grass (Arthraxon hispidus), and Big Bluestem (Andropogon gerardii) are especially problematic. Urban development is also a serious threat in the region. The last population of Earleaf False Foxglove (Agalinis auriculata) in Virginia was in a northern Piedmont grassland that was converted to a housing development.
Figure 1. Most of the sites we sampled had high native plant diversity and low exotic species importance. Exotic species importance = (number of exotic species + total abundance of exotic plants) / 2
We at the Clifton Institute are working with power companies, government agencies, and private landowners to improve management of these special grasslands. We have also designed a seed mix to use for meadow plantings in our area so that wildflower meadow plantings can provide excellent habitat while also being beautiful and easy to establish. Many characteristic northern Piedmont grassland plants are not available from commercial seed sellers, and we are collecting seeds and distributing seeds and seedlings to the local community for restoration projects.
The Virginia Native Plant Society provided financial support for this project, and Manassas National Battlefield Park and Fairfax County Park Authority granted research permits.