In early May I made the familiar drive east across Tennessee for a week of field work in and around the large Tennessee Valley Authority powerline corridors that cross the surface of the Cumberland Plateau. This work is part of a multi-year study looking at the value of these open rights-of-way to grassland biodiversity, specifically to plants and their insect pollinators.
The multi-year study is being conducted with our partners at the Tennessee Valley Authority (TVA), the Mississippi Entomological Museum, and the Electric Power Research Institute. On this trip, I would be meeting up with members of the project’s botany field team – Will Overbeck and Brittney Georgic of SGI and Adam Dattilo, Botanist with TVA.
Heart-leaf golden Alexanders (Zizia aptera) and hairy phlox (Phlox amoena) in a powerline right-of-way in Cumberland County, Tennessee. Photo by Theo Witsell.
As I discussed in a couple of previous blog articles (article 1 and article 2), multiple lines of evidence suggest that this flat to gently rolling landscape historically supported a diverse mosaic of open to semi-open habitats ranging from patch communities like open acidic bogs, sandstone glades, and prairies, to more extensive areas of open pine and oak savannas and woodlands. It’s these more open ecosystems that support most of the rare species on the Plateau surface and remaining examples of these habitats are high conservation priorities.
Unfortunately, however, these ecosystems have been heavily converted to human uses such as agriculture, non-native pastures and hayfields, and pine plantations, and much of their original vegetation has been lost. That’s in contrast to the naturally closed forests of the more rugged slopes and gorges of the region, which are largely still intact and make up most of the protected areas today.
It's no surprise to biologists working in this region that these open habitats historically supported great grassland biodiversity, with species like American chaffseed (Schwalbea americana), green pitcher plant (Sarracenia oreophila), tawny cotton-grass (Eriophorum virginicum), and Red-cockaded Woodpecker (Dryobates borealis).
For the crew working on this project, it’s also no surprise that the powerline rights-of-way are significantly more interesting botanically than the surrounding woods. Species richness (the number of species present) is usually several times higher in the rights-of-way than in the woods, and the rights-of-way are rich in what we call conservative heliophytes, or “grasslandy species”- those plants that are found only in more stable, mature grasslands, or in surrogate habitats in areas that were historically grassland.
Granite Gooseberry (Ribes curvatum) in an open woodland on the Cumberland Plateau in Sequatchie County, Tennessee. It is listed as threatened in the state of Tennessee. Photo by Theo Witsell.
On the first day out Will and I were cataloging plants in the North Chickamauga Creek Wildlife Management Area, near Dunlap, Tennessee, where we saw several good species. There was the granite gooseberry (Ribes curvatum, Tennessee state-listed Threatened) in open woodlands above cliff lines as we drove into the area, and when we got to the powerline we knew we were in a grassland remnant.
We quickly found large swaths of little bluestem (Schizachyrium scoparium), Elliott’s bluestem (Andropogon gyrans), Indiangrass (Sorghastrum nutans), and wildflowers like Sampson’s snakeroot (Orbexilum pedunculatum), sharp-leaf St. John’s-wort (Hypericum virgatum), several species of boneset or thoroughwort (Eupatorium spp.), goldenrods (Solidago spp.), asters (Symphyotrichum spp.), and many other species. We also found bog oat-grass (Danthonia epilis, Tennessee state-listed Special Concern), which we had seen at other sites in previous years.
We even saw a few young saplings of blackjack oak (Quercus marilandica), a species of dry oak savannas and woodlands, at the edge of the right-of-way. It isn’t uncommon to find old blackjack oaks persisting in now-closed canopy woodlands but it’s much less common to see seedlings or young specimens, which indicate that they're still reproducing. Seedlings are typically only found in open conditions such as the powerline corridors or open roadsides.
I mentioned to Will that we should keep our eyes out for any areas with groundwater seepage within the right-of-way because they could have any of several rare acidic bog species known from the region. Then, shortly after saying this I spied a patch of bright yellow amid the little bluestem in a wet spot below some rock outcrops. I stepped in closer to confirm my suspicions and shouted “Yes! Zig-zag Bladderwort!”
Zigzag Bladderwort (Utricularia subulata) in a powerline right-of-way in Sequatchie County, Tennessee. It is listed as threatened in the state of Tennessee. Photo by Theo Witsell.
Zig-zag Bladderwort (Utricularia subulata) was on a list of rare target species that we had compiled in the days before we left for this trip. Listed as Threatened on the Tennessee Rare Plant List, it's a species of wet, open, acidic grasslands, and is one of a handful of carnivorous plants known from Tennessee. It was known from several historical collections on the Plateau surface, including several from a well-known large open bog along Glade Branch near Clarkrange where it was collected in the 1930s and 40s, but had not been seen recently on the Plateau surface. We photographed these plants, did a count, gathered other data for TVA and the Tennessee Natural Heritage Program, and I collected a few individuals for an herbarium specimen since the species was a county record (it had not been previously recorded from Sequatchie County).
This pattern of finding concentrations of rare species dependent on open habitats on the Plateau surface has been the rule for our work in the region. In an earlier blog article I featured the rare species we had found in the first two years of this project and here was another to add to that list.
The next day we went to a very interesting powerline right-of-way in the Cumberland Trail State Park near Crab Orchard that was rich in grassland and open woodland species. Immediately after getting there we encountered a large population of heart-leaf golden Alexanders (Zizia aptera) - thousands of individuals in full bloom, giving a pale yellow glow to the right of way.
There are also large stands of hairy phlox (Phlox amoena), and scattered plants of eastern wild indigo (Baptisia tinctoria), New Jersey tea (Ceanothus americanus), dwarf iris (Iris verna var. smalliana), Culver’s root (Veronicastrum virginicum), white colic-root (Aletris farinosa), rough blazing-star (Liatris aspera), bastard toadflax (Comandra umbellata), and the uncommon Catesby's false bindweed (Calystegia catesbeiana), along with many other grassland species. On previous visits to this site later in the season the team had documented several other interesting and uncommon species including the small spreading pogonia orchid (Cleistesiopsis bifaria) and the rare wood lily (Lilium philadelphicum).
We have two more trips to these sites scheduled for this year and anticipate finding more interesting species. Watch this blog for any interesting updates.
Dwarf iris (Iris verna var. smalliana) in a powerline right-of-way in Cumberland County, Tennessee. Photo by Matt Thorn.
THEO WITSELL, SGI CHIEF ECOLOGIST
Theo explores our native grasslands, gathers and synthesizes data on their ecological and historical significance, and provides scientific direction and ecological context for the Southeastern Grasslands Initiative.