Thursday, January 1, 2015

Pennyroyal Plain Prairies

One of the South's Great Grassland Systems

When people think about grasslands of North America, most picture a flat to rolling landscape typical of the Great Plains of Kansas or Iowa, with tall grasses waving in the wind for as far as the eye can see. If you close your eyes you can almost see it as it was 250 years ago: herds of bison thundering across vast prairies, prairie chickens dancing at dawn, butterflies flitting across dense swards of blazing stars. Would you believe that I just described a prairie landscape that once occurred in Tennessee known as the Pennyroyal Plain prairie? This prairie system, more commonly referred to as the “Big Barrens,” was historically one of the largest prairie types in the Southeast. This vast crescent-shaped prairie extended more than 200 miles in length and averaged 20-35 miles wide. Today, only tiny vestiges remain.

Map of the Pennyroyal Plain and Elizabethtown Plain with black areas
indicating former prairie (Baskin et al. 1994).

Prior to 1800, the Pennyroyal Plain supported vast herds of bison and elk. Prairie chickens lived on the Pennyroyal at least through the 1810's. Wolves, black bears, and cougars stalked the prairies. Early observations and descriptions of the vast Pennyroyal Plain Prairie were provided by numerous early settlers, naturalists, and explorers, including French botanists Andr√© Michaux, Francois Andr√© Michaux, and the future king of France, Louis-Philippe. Albert Ross, one of the early settlers of Clarksville, TN, whose family is the namesake for the community of Rossview east of Clarksville moved to the area in 1812 and described the area between northern Montgomery County, TN and Hopkinsville, KY as follows: 

“Far as the eye could reach, they [the grasslands] seemed 
one vast deep-green meadow...only a few clumps of trees 
and now and then a solitary post-oak were to be seen.”

-Albert Ross (undated)

      The Pennyroyal wasn't just a vast prairie. It was in fact a matrix of mesic tall grass prairie, wet prairie, shorter mid-grass prairie, oak-hickory woodland, savanna, riparian forest, limestone barrens, limestone glades, swamps, and depression ponds. Natural sinkhole ponds dotted the landscape in many areas of the Pennyroyal Plain historically but very few high-quality remnants remain. C.W. Short, an early 19th century botanist stationed in Hopkinsville, Kentucky, provided some the best accounts of these prairie sinkhole ponds:

    "Now, would burst upon the view a smooth sheet of water, 
skirted with the blue and purple hues of the Pontederia 
and Decodon, intermixed with the scarlet berries of the Prinos, 
whilst its surface was covered over with the large and floating leaves 
and splendid flowers of the Cyamus; and then, in endless vistas, 
was stretched before the eye a waving sea of gigantic grasses."

-C.W. Short (1836)

This GoogleEarth map shows a typical Pennyroyal Plain landscape in
Christian Co., KY with water-filled sinkholes. The circled sinkhole is one
of only two localities in Kentucky known to support the very rare
Hall's bulrush (Scheonoplectiella hallii) and mudbabies (Echinodorus tenellus). 

The once vast prairie country of the Pennyroyal began changing soon after the dawn of the 19th century. The major factor that kept the prairie alive was annual fire. Many early writers note the fires that burned the prairies annually. Many attributed this practice to the Indians from adjacent regions who used the area as hunting grounds. Burning by Indians decreased in the first couple of decades of the 19th century and ceased when they were forced west to Oklahoma during the Trail of Tears in 1838-1839. White settlers continued to use fire well into the 20th century but on a much reduced scale. Bison were extirpated from the area by 1800; the effects of their grazing and trampling of the prairie ceased. Undoubtedly, bison were a major force in maintaining the prairie. 

Lightning fire would also have played an important role in the original maintenance of the prairie ecosystem. Just imagine a scraggly, lone blackjack oak standing on a low hill, emerging out of a clump of winged sumac; a sentinel keeping watch over a vast open, grassy landscape. It is late July and the Pennyroyal Plain is parched from the paucity of summer rain. The prairie grasses are dry and crunchy; everything appears greenish-brown and few plants are in flower. In the late afternoon, thunderstorms begin to roll in from the west, bringing with them an impressive lightning storm but little rain. A single bolt of lightning illuminates the darkening sky, striking the solitary oak, igniting it and the surrounding grass. Soon, fire is racing out across the open prairie leaving a black, scorched earth in its wake. Lightning fires like this could have burned for days across the Pennyroyal because unlike adjacent ecoregions where streams and rivers are abundant, the Pennyroyal has very little surface water due to the karst topography. This means that fires either must have either burned themselves out or be extinguished by rainstorms.  

Before the middle of the 19th century the landscape of the Pennyroyal was already undergoing major transformation. Numerous writers wrote firsthand accounts of how the prairie they once saw as children had turned to woodlands by the time they reached adulthood. Most attributed the succession of the prairie to woodland to the dramatic decrease in fire in the area. The decrease likely came as a result of passive fire suppression. As whites settled the area, establishing farms throughout the region,   the landscape would have become much more fragmented. The natural prairie would become broken by small farms and roads, creating fire breaks that didn't exist previously. With more settlers and more fragmentation, the ability for fires to sweep across the landscape would eventually diminish altogether. Fire suppression is the main factor that eliminated the Pennyroyal Prairie.

Ft. Campbell Army Base: US Military Saved the Pennyroyal Prairie

Today, most people would find it hard to believe or imagine Ross's early description of the Pennyroyal landscape. That's because most of the Pennyroyal today has been converted to a matrix of cropland (especially wheat, tobacco, corn, soybean, canola) and small isolated woodlots. It would be hard for most folks to imagine that 250 years ago many of today's major highways in the Pennyroyal region were established along the ancient "highways" or buffalo traces of the bison.

There are no known examples of pristine "virgin" prairie left in the Pennyroyal. It is estimated that more than 95% of the original prairie acreage has been destroyed by agriculture or succession to woodlands and forests. Today, the vast majority of known prairie remnants in both Tennessee and Kentucky are restricted to Fort Campbell Army Base. Even the remnants that now exist at Fort Campbell were once under cultivation or pasturage prior to the base's establishment in the 1940s.

Fort Campbell Army Base (red polygon) is home to 99% of remaining
Pennyroyal Plain prairie remnants. The prairie once covered most of the area in green.

On the 102,000 acre Ft. Campbell base there are approximately 20,000 acres of prairie remnants. About half of these exist in a fairly contiguous region of the impact zone in the northwestern corner of the base. The other half occurs as scattered small remnants throughout the rest of the base. These remnants are threatened by their small size, fragmented nature, and invasion by non-native species like shrubby lespedeza (Lespedeza bicolor) and Chinese lespedeza (L. cuneata). Many of the remnants are being monitored by Ft. Campbell biologists and are managed by prescribed fire.

Fort Campbell Army Base along the Tennessee and Kentucky state line 
northwest of Clarksville, TN. The large brown areas in the western and 
northwestern portions of the base are large prairie remnants. More than 99% 
of the Pennyroyal Plain prairie remnants that exist are found at Fort Campbell.

The prairies at Fort Campbell represent the best remnants left of this system. Understanding their structure, composition, and variation will be critical for future establishment and restoration efforts of other prairies in the region. At least three major types of prairie are found at Fort Campbell, including wet prairie, mesic prairie, and dry prairie. 

Wet prairie are the rarest and least understood type. Important grasses of wet prairie include Eastern gamagrass (Tripsacum dactyloides), prairie cordgrass (Spartina pectinata), Virginia iris (Iris virginica), rushes (Juncus spp.), sedges (Carex alata and many other species), bulrushes (Scripus georgianus), redtop panic grass (Coleotaenia rigidula), seedbox (Ludwigia alternifolia), and swamp milkweed (Asclepias incarnata).

Mesic prairie is dominated by thick stands of tall grass, sometimes up to 10 ft tall. Typical grasses of mesic prairie include Indian grass (Sorghastrum nutans), big bluestem (Andropogon gerardii), and plume grasses (Erianthus alopecuroides). Rare species associated with this habitat include sweet coneflower (Rudbeckia subtomentosa), compass plant (Silphium laciniatum), and inland muhly grass (Muhlenbergia glabriflorus).

Mesic prairie, Fort Campbell Army Base.
Photo by: Dr. E.W. Chester

Dry prairie is the shortest of the three types. It is dominated by little bluestem (Schizachyrium scoparium), three-awn grass (Aristida purpurascens), and a rich variety of sunflowers, asters, goldenrods, and thoroughworts. Prairie willow (Salix occidentalis) is a common shrub in dry prairie. Rare plant species found in this community include earleaf false foxglove (Agalinis auriculata), Skinner's false foxglove (Agalinis skinneriana), and barbed rattlesnake root (Nabalus barbatus).

Dry prairie, Fort Campbell Army Base.
Photo by: Dr. E.W. Chester

Some areas at Fort Campbell may have existed as open oak savannas, especially those in more rolling landscapes. Primary oaks would have been post oak (Quercus stellata) and blackjack oak (Q. marilandica). The photos below represent savanna-like areas at Ft. Campbell Army Base.

Examples of savanna-like areas at Ft. Campbell.
Top photograph was taken by Dr. E.W. Chester who said
"this is the best photograph of the 'barrens" I've ever made."
Bottom photo is of Dr. Chester in a giant stand of blazing star (Liatris spicata)
Photos by: E.W. Chester

Prescribed fire is used to manage many of Fort Campbell's prairie remnants. Those in the impact zone are frequently burned by fires that ignite from firing exercises. Without question, if Ft. Campbell didn't exist then neither would the Pennyroyal Plain prairies. Without the base, those on present base lands would today be agricultural fields, subdivisions, woodlots, or cattle pastures. This is a great example of how military lands are extremely important for preserving some of our rarest ecosystems and species.

Smoke from a prescribed fire at Fort Campbell Army Base.
Photo by: Dr. E.W. Chester

The Pennyroyal Prairie Outside of Ft. Campbell

Today, only a handful of very small prairie remnants exist outside of Fort Campbell, but these are constantly under threat. Well into the 20th century, small isolated prairie remnants existed along rural roadsides, in strips beneath powerlines, along the edges of crop fields, in thin strips along the edges of woodlands, or sandwiched between railroads and highways. Many were no larger than half-acre or may have only occupied a few dozen square feet. It was relatively common for botanists working in Kentucky and Tennessee from the 1930s-1970s to observe such prairie remnants in the Pennroyal. One such remnant that was studied up until the late 1900s was the so-called Warfield Barren or Warfield Prairie (described below).  

One such remnant is the Warfield Prairie located in extreme northeastern Montgomery County, Tennessee. It exists as a linear strip sandwiched in a 30-50 foot wide, 1.5 mile long strip between US Hwy 41 and the CSX Railroad just southeast of the town of Guthrie, Kentucky. Recently, CSX Railroad has collaborated with the Tennessee Department of Transportation (TDOT), the Tennessee Division of Natural Areas (TDNA), Austin Peay State University (APSU), and the Botanical Research Institute of Texas (BRIT) to establish the Pennyroyal Plain Railroad Prairie Natural Area. This is the only Pennyroyal Plain prairie remnant in Tennessee that is known to exist outside of Ft. Campbell and it is a rare example of a wet prairie. Identifying, inventorying, and monitoring of these remnants is needed.

Warfield Prairie remnant as it has appeared for many years.
The prairie grasses are routinely mowed and kept short.
Warfield Prairie remnant, Montgomery Co., TN as it
appeared in 1988 before regular mowing of roadside.
Photo by: Dr. E.W. Chester, 1988

Style of planned kiosk at the
Pennyroyal Plain Prairie RR Natural Area

By the late 20th century sightings of prairie remnants became rare indeed. This was because of changes in highway maintenance. During the 1990s, many highways were widened from two to four lanes, obliterating the former remnants. Roadside embankments that once were grassy or brushy, supporting prairie species, became mowed on an annual basis, thus preventing the prairie flora from flowering and setting seed. To compound the problem, invasive species like common fescue (Schedonorus arundinaceus), Chinese buschclover (Lespedeza cuneata), and Johnson grass (Sorghum halepense) out-competed prairie species. In the early 2000s (and increasing thereafter), there also seemed to be a precipitous increase in the amount of herbicide used to treat roadsides, railroad rights-of-way, fencerows, and ditches. The end result is that roadside remnants, which are the last vestiges for many of the South's great prairie systems, have now become nearly completely eliminated. Once they are gone, the hope for restoration using local genotype seeds will be gone, too.

Future Conservation of the Pennyroyal Prairie

There is so much that needs to be done to conserve the vanishing Pennyroyal Plain Prairie.  

The first goal is to identify known remnants. Remnants are few and far between but they do exist and there are likely many small patches that have never been discovered on private lands. 

APSU and BRIT are also planning to partner with Roundstone Native Seed LLC (Munfordville, KY) and Dunbar Cave State Park in Clarksville, TN to establish a 13-acre prairie at the state park and a 2-acre prairie at the Austin Peay State University Environmental Education Center. The goal is to establish diverse local genotype prairies that mimic those nearby at Ft. Campbell. 

More work is needed to educate the general public about the importance of prairie restoration. Plans are in the works with Julian Campbell of the Bluegrass Woodland Institute to establish a public field trip series to visit remnants and discuss their ecology and conservation. Additionally, we plan to establish a visiting public lecture series intended to be delivered to conservation organizations, citizen groups, agencies, and other groups across the Pennyroyal region. 

Eventually, the plan is to be able to once again see landscapes like the one below return throughout the Pennyroyal Plain.

The largest single open field in Tennessee is this degraded prairie remnant at Ft. Campbell, Montgomery Co., TN. Landscapes like this, where no trees could be seen on the horizon were once the norm for the Pennyroyal Prairie 200 years ago. Can we bring this landscape back by creating a network of prairie preserves throughout the Pennyroyal region?

For more information on Southeastern grasslands, I strongly encourage reading Forgotten Grasslands of the South by Dr. Reed Noss (Univ. of Central Florida). It provides an incredible perspective on the diversity, ecology, and history of the Southeastern grasslands not provided anywhere else.

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