Acalcareous glade is a type of ecologicalcommunity that is found in the centralEastern United States.Calcareousglades occur wherebedrock such aslimestone occurs near or at the surface, and have very shallow and littlesoil development. Due to the shallow soil and the extreme conditions created by it,trees are often unable to grow in the glades. This creates ahabitat that is usually sunny, dry, and hot. Calcareous gladevegetation is more similar to that of adesert habitat than a grassland, being dominated by small spring annuals with occasionalgeophytic orsucculentperennials.
The usage of the words "glades" and "barrens" to describe dry, rocky communities in the United States is not uniform, and the terms are often used interchangeably.[1] Calcareous glade communities can intergrade with dry rocky prairies, particularly in sloping habitats. Due to their unsuitability for agriculture, glade communities have survived to the present day at a higher rate than deeper-soil prairie communities.[1]
TheInterior Low Plateau is a region in theUpper South that is known for its calcareous glade communities. This region is centered inTennessee andKentucky, and extends into northernAlabama, and southernIllinois, southernIndiana, and southernOhio. These glades are best developed in the area of theCentral Basin (or Nashville Basin) in Tennessee, where they are geographically widespread and harbor high levels of endemism. Outside of the Central Basin, calcareous glades are found in lower numbers throughout the Interior Low Plateau, and speciesendemism is greatly reduced. Glades in the Interior Low Plateaus are characterized by species such as one-flower gladecress (Leavenworthia uniflora), limestone skullcap (Scutellaria parvula), widow's-cross stonecrop (Sedum pulchellum), poverty dropseed (Sporobolus vaginiflorus) and glade violet (Viola egglestonii).[2]
The limestone glades of the Central Basin in Tennessee are often called "cedar glades". The name comes from the abundance of eastern red cedar (Juniperus virginiana) that occurs on the margins of the glades or in cracks in the bedrock where the roots can gain a foothold.
Many of the characteristic plants that grow in the limestone glades of the Central Basin are endemics that occur nowhere else, or disjunct populations of plants that are widespread in theprairies of the central U.S.[3] Some species with highly restricted ranges that occur in the glades of the Central Basin include the Tennessee coneflower (Echinacea tennesseensis), Pyne's ground plum (Astragalus bibullatus), leafy prairie clover (Dalea foliosa), Tennessee milkvetch (Astragalus tennesseensis), Nashville breadroot (Pediomelum subacaule), and limestone fameflower (Phemeranthus calcaricus).
These glades can be saturated with water in the winter and spring, leading to "xerohydric" (dry/wet alternating) conditions.[4]
The central basin (or Nashville Basin) of Tennessee is one of the largest areas containing limestone glades. Because of the rapid growth of metropolitanNashville and the surrounding cities ofMurfreesboro andLebanon, many of the limestone glades have been destroyed by development. The State of Tennessee and the Nature Conservancy have established a number of parks and preserves to protect important plant populations.Cedars of Lebanon State Park inWilson County andLong Hunter State Park inDavidson County both protect substantial limestone glade ecosystems.
The limestone slope glades ofKentucky are a globally vulnerable habitat consisting of limestone glades found on hillsides, which are wet in the spring but become very dry in the rest of the year. This provides habitat for unique species such as necklace glade cress, Butler's quillwort, and Crawe's sedge.[5]
This is a list of calcareous glade-adapted plant species considered endemic to the Interior Low Plateau region. Some are found in only a single county of a single state.[6]
Calcareous glades are well developed in theOzark Mountains. InMissouri, the majority of these glades are found ondolomitic limestones, with less than 1% formed fromcalcitic limestone.[1] Species indicative of Ozarkian calcareous glade communities includeCheilanthes feei (slender lip fern),Echinacea simulata (pale purple coneflower),Heliotropium tenellum (pasture heliotrope),Isoetes butleri (limestone quillwort),Oenothera macrocarpa (Missouri evening primrose), andOphioglossum engelmannii (limestone adder's-tongue).[1] In Missouri,Physaria filiformis (Missouri bladderpod) is a species restricted to calcitic limestone glades.[1]
TheRidge-and-Valley Appalachians, which extend north from Pennsylvania south to Alabama, have significant calcareous glade communities.[7] These glades often have dolomitic soils, resulting in a high magnesium content (in contrast to the glades of the Nashville Basin). In Virginia, these glades provide habitat for rare magnesiophiles such as Addison's leatherflower (Clematis addisonii), tall larkspur (Delphinium exaltatum), smooth coneflower (Echinacea laevigata), and glade wild quinine (Parthenium auriculatum).[8]
At the southern end of the Ridge and Valley in Alabama inBibb County, species endemism of glade communities peaks. This area, known as a Ketona Dolomite Outcrops, was first recognized as ecologically significant in 1992. Since its discovery, eight new plant taxa to science have been described from this region, in addition to the 60 species of conservation concern found in or around this community.[9] Endemic species of this area includeCastilleja kraliana,Dalea cahaba,Liatris oligocephala,Lithospermum decipiens, andSpigelia alabamensis.