Alabama proved to be a very interesting place to botanize, in part because of its diverse geology. We visited seven areas in the northern part of the state, some principally limestone (producing neutral to somewhat alkaline conditions) and others primarily sandstone or granite (both usually acidic). A key event in the geological history of the region was relatively recent uplift of much of the northern part of the state. This uplift added gradient to the watercourses, increasing their capability to cut canyons and through erosion create interesting features such as waterfalls and alcoves. The result was a great diversity of microhabitats in what had previously been a much more uniform region. This statement applies even more strongly to underwater habitats such as in stream beds, which became differentiated during uplift. The new species that developed in individual tributaries and rivers often remained quite isolated from other recently evolved species because of the relative difficulty of dispersing upstream, against the current, into a different tributary. The resulting diversity of freshwater fish, mussels, and other aquatic life is among the highest in the country.
The first location we visited was Little River Canyon National Preserve, in the northeastern portion of the state. Of particular interest to us was the special community of plants that occur on granite outcrops, where water collects in shallow depressions on the surface of the bedrock, and very thin soils eventually are deposited. At Lynn Overlook, which has superb examples of wet granite outcrops, the two most abundant species in flower were both new for us, and an interpretive sign mentioned several other species flowering later in the year, which we also have not seen. It is always exciting to encounter new and unique habitats like these!
We spent a full day hiking at nearby DeSoto State Park (SP), finding more wet granite outcrops (behind Site 71), and seeing a nice assortment of Appalachian plants, including five new species, and a year bird – Worm-eating Warbler. Next on the agenda was the Keel Mountain Preserve, administered by The Nature Conservancy (TNC). An interesting feature of this preserve, which is on limestone, is a fairly tall waterfall that plummets directly into a sinkhole, where it disappears – the water drains out underground rather than forming a pool on the surface. We stayed two nights in Monte Sano SP, in the hills east of Huntsville, and on the second morning had a small flight of some of the later migrant warblers, including Bay-breasted and Magnolia.
Moving next to the northwest quadrant of Alabama, we visited another TNC property, Prairie Grove Glades Preserve. The unit protects high-quality cedar glades, which are areas of short vegetation occurring on thin soils over bedrock. Typically, Eastern Redcedar trees, Juniperus virginiana, break up the open habitat into somewhat discrete “rooms”. This lovely habitat reminded me of the alvar barrens found in restricted areas of the Great Lakes, which likewise provide superb botanizing. Despite considerable rain, we found six new plants, one belonging to a particularly interesting genus, Leavenworthia. These plants, referred to as gladecresses, are in the mustard family. Found only in the U.S., there are just 8 species in the genus, all but one of which are rare and/or have extremely limited distributions, mostly in the Southeast.
We were aided at Prairie Grove Glades by a plant list compiled by Brian Finzel, linked from the Alabama Native Plant Society. His database of flowering dates for many locations in northern Alabama and central Tennessee was of great help in locating good places to visit. Scanning his master list, I noticed one very rare plant, Croomia pauciflora, which is the only North American member of its family, Stemonaceae. My research over the winter had not uncovered any promising leads for locating this species, so I had previously relegated it to the hopeless cause category. Crossing my fingers, I sent an e-mail to Brian and asked if he could recommend any location for Croomia, and he quickly responded with coordinates for a site just a couple hours away. We immediately changed plans and later that day were admiring the tiny but bizarre flowers of this very unusual plant!
One spot we visited based on Brian’s checklists was the Sipsey River Picnic Ground, in Bankhead National Forest. This area had pretty sandstone canyons with waterfalls, and we were excited to find in one alcove the unusual Filmy Fern, Vandenboschia (Trichomanes) boschiana. This delicate fern is just one cell thick, an adaptation to the low light levels in the deeply shaded rock shelters it favors. This species occurs mostly in Kentucky and Alabama, but also rarely in 11 bordering states. Like several other ferns, it is found essentially exclusively in sandstone alcoves, which are formed when harder rock lies above softer material, and water flowing down the face of exposed rock layers erodes the softer rock more quickly, undercutting the harder material above. This creates a sheltered area that is roughly triangular in cross-section, with the roof sloped back into the bedrock. Sometimes, water flowing over the lip creates a free-falling waterfall, as in the photo below, of Yahoo Falls, Kentucky, where we first saw Filmy Fern in 2002.
A key characteristic of such alcoves, especially the furthest reaches of the deeper ones, is that they have milder and less variable temperatures than opener areas just feet away, because the thermal mass of the bedrock mediates temperature fluctuations. Humidity also tends to be high, from seepage and waterfall spray, and the heat capacity of the water vapor also suppresses temperature change. The result is a stable, warm, moist microhabitat. Remarkably, Filmy Fern and several related species, which are tropical relicts from more temperate climates in the geological past, have survived in these tiny refugia.
Our last destination in Alabama was Cane Creek Canyon Nature Preserve, a private property owned by Jim and Faye Lacefield, but which is open to the public. The preserve protects a number of large moist alcoves – the most magnificent we have ever seen – as well as several open glades containing an impressive number of rare plants. The alcoves harbor Filmy Fern and even rarer relatives, some of which have evolved to dispense with half of the usual fern reproductive cycle, an adaptation to their limited and isolated habitat. Jim and Faye have put in a marvelous trail system with a detailed map, shelters, and even drinking water stations. Jim invited us to join him in the afternoon for an ATV ride through the preserve, as he would be giving a tour to a new intern. This was a total blast! We saw a number of uncommon to rare plant species, including Allegheny Spurge, Pachysandra procumbens, representing our 240th vascular plant family; French’s Shooting Star, Dodecatheon frenchii, a rarity occurring only in the alcoves; Kentucky Yellowwood, Cladrastis kentuckea, a rare tree with its closest relatives in east Asia; and Ginseng, Panax quinquefolius, made rare by its harvest for reputed medicinal properties.
Jim is an expert on geology and its relationship to biodiversity, and has published a popular book, “Lost Worlds in Alabama Rocks: A Guide to the State’s Ancient Life and Landscapes”, now in its second edition. He explained to us about the importance of uplift in Alabama’s biodiversity, and the role of sandstone alcoves as subtropical refugia — and I hope I have done these topics justice earlier in this post. We had a great time during our two days wandering in the preserve, and thoroughly enjoyed the stimulating discussions with Faye and Jim, who were very kind hosts. This was a wonderful way to finish up our transect of northern Alabama, a fascinating area to which we will return!