Habitat
SUMMARY: Scutellaria montana is typically found in rocky, shallow soils, and on submesic to xeric, well-drained, slightly acidic oak-pine forests in the Ridge and Valley and Cumberland Plateau provinces of northwestern Georgia and adjacent southeastern Tennessee. In Georgia, it has been reported from elevations of 189 to 265 m on steep, lower slopes of all aspects. In Tennessee, the elevation range of the species is much greater, with one concentration of sites at 200 to 320 m on slightly sloping to steep lower to mid-slopes on the Upper Mississippian Pennington Formation. The other concentration is at 400 to 540 m on gentle to somewhat steep slopes of small ravines near the escarpment on the Cumberland Plateau, on Lower Pennsylvanian sandstone and shale (Bridges 1984). The soil is always rocky and somewhat shallow, with plants rooted in deeper soil between boulders, or on as little as 3 cm of soil over rocks (Collins, unpublished manuscript). The species appears to have little specific habitat preference, occurring in localized areas within its known range. It is unclear what limits the northern edge of its distribution.
FULL DESCRIPTION: Scutellaria montana is typically found in rocky, submesic to xeric, well-drained, slightly acidic slope, ravine, and stream bottom forests in the Ridge and Valley and Cumberland Plateau provinces of northwestern Georgia and adjacent southeastern Tennessee (and possibly northeastern Alabama). In Georgia, it has been reported from elevations of 189 to 265 m (620 to 870 feet) on steep, lower slopes of all aspects (Collins 1976). In Tennessee, the elevation range of the species is much greater, with one concentration of sites at 200 to 320 m (650 to 1050 feet) on slightly sloping to steep lower to mid-slopes on the Upper Mississippian Pennington Formation. Another concentration of Tennessee sites is at 400 to 540 m (1300 to 1780 feet) on gentle to somewhat steep slopes of small ravines near the escarpment on the Cumberland Plateau, on Lower Pennsylvanian sandstones and shales. The breadth of its occurrence in relation to geological strata is remarkable - shale, chert, limestone, and sandstone from Cambrian to Pennsylvanian age, essentially most of the major slope-forming formations of the region. The soil is always rocky and somewhat shallow, with plants rooted in deeper soil between boulders, or on as little as 3 cm of soil over rocks (Collins 1976).
In terms of natural community types, Scutellaria montana occupies types which are typical for the region and occupy a large percentage of the lesser disturbed slopes within and beyond the known range of the species. In Wharton (1978), these community types are Armuchee Ridge Forest, Oak-Pine Forest of the Great Valley, and possibly Submesic Ridge and Slope Forest (Sedimentary Region). These types are difficult to distinguish in absolute terms, as are the community types supporting Scutellaria montana in Tennessee. Perhaps a more broadly defined type, such as "Dry-mesic acidic slope forest - Upland Oak-Pine Region Type" may be more appropriate, with numerous subtypes being possible throughout the range of the type (Virginia to Alabama and Tennessee). The distinguishing features of this type are 1) At least some natural pine occurrence for long periods [typically Pinus echinata or P. taeda, less commonly P. virginiana or P. palustris]; 2) Predominately oaks and hickories as canopy species, with scattered more mesic species; 3) Predominately deciduous shrub layer, with some evergreen Vaccinium [not dominant]; 4) Moderately dense herb layer (typically 20-50%) of a mixture of mesic and somewhat xeric species (Desmodium spp., Hexastylis spp., Chimaphila maculata characteristic); 5) Developed on well-consolidated paleozoic to pre-cambrian strata, often with some exposed rock. This is a common natural community in the Piedmont (VA, NC, SC, GA, AL), extreme Southern Blue Ridge (GA, AL) and southern Ridge and Valley and Cumberland Plateau (GA, AL, southeastern TN) on sites typical of these regions.
Scutellaria montana is associated with several of the same species throughout its range, while other associates differ in relation to degree of moisture of the site, and from northernmost to southernmost populations. Several oak species usually dominate the canopy, most often Quercus alba, Q. velutina, and/or Q. montana, less often Q. stellata and Q. rubra. Four hickory species are present from at least one site (Carya ovata, C. glabra, C. tomentosa, and C. pallida.) Pines are at least a minor component of the canopy at all sites, with Pinus echinata being most typical (less often P. virginiana, P. taeda, and P. palustris). At least at the Tennessee sites, other hardwoood species, often of more mesic affinities, are present in the canopy; Liriodendron tulipifera and Liquidambar styraciflua are the most frequent of these species.
The most typically associated subcanopy species is Cornus florida, which is extremely common in the natural community type. Numerous other subcanopy and shrub species may be present, as well as many transgressives of the canopy species. Vaccinium arboreum, Oxydendron arboreum, Sassafras albidum, and Calycanthus floridus are present at several sites, with Cercis canadensis, Vaccinium stamineum and Vaccinium pallidum said to be typical of Georgia sites (Colllins, unpublished manuscript).
The herbaceous layer associates are perhaps the most critical species in explaining Scutellaria montana habitat and occurrence, yet are even more varied than the woody associates, with at least 30 species present at more than one site. Those which are common associates in Georgia (Collins 1976) and are also present at some Tennessee sites include Dioscorea villosa, Spigelia marilandica, and Hexastylis arifolia. Several other species are common associates in Georgia, but are not known to be closely associated in Tennessee. These include Polygonatum biflorum, Geranium maculatum, Arisaema triphyllum, Asclepias quadrifolia, Trillium catesbaei, Trillium cuneatum, Chimaphila maculata, and Hypoxis hirsutus. Several additional species are associated with Scutellaria montana at two or more of the Tennessee sites, including the woody vines Smilax glauca, Vitis rotundifolia, and Parthenocissus quinquefolia, as well as Cynoglossum virginianum, Desmodium glutinosum, Lysimachia tonsa, Galium circaezans, Sanicula canadensis, Pteridium aquilinum, Polymnia uvedalia, and Coreopsis major.
The associated species of Scutellaria montana include both somewhat mesic and somewhat xeric indicator species for the region, with the extremely mesic species and most xeric species lacking. The relatively wide range of moisture preferences of associates is attributable in part to variation between sites, but much of this variation is due to the microtopography diversity within many of the sites. The steep, rocky surfaces result in both quite xeric shallow soil areas over and in small cracks between rocks, and deeper, moister soils in larger crevices in positions where runoff is channeled. The relationship of Scutellaria montana to this microtopographic variation is either not very specific, or as yet undetermined, as it can be found in many microhabitats at most sites. It does seem to be in areas with less herbaceous cover than its surroundings, and apparently does not compete well with many of its herbaceous associates. This is probably particularly true with regard to rhizomatous, colony-forming species which, once established, could easily crowd out Scutellaria. Nearest neighbor studies at one of the Tennessee sites (Bridges and Hawks 1984), indicate that S. montana is often found 3"-10" away from rhizomatous plants such as Calycanthus floridus, Parthenocissus quinquefolia, and Desmodium nudiflorum, and most shaded by a subcanopy tree of Cornus florida and a canopy Quercus alba. This situation obviously varies by site, but perhaps indicates the tenuous balance between S. montana and its larger, more aggressive, herb, vine, and shrub associates.
Ecology
The life history of Scutellaria montana has not been specifically studied, and relatively little of it is known. Mature nutlets were not even seen until about 1983 by workers at Shorter College, thus indicating the early stage of work on the biology of the species. Collins (unpublished manuscript) summarizes the general life cycle as follows: "Nutlets are released from late June through early July (mid-June to mid-July?), overwinter, and apparently germinate in late March. Mature individuals that have perennated as rootstocks begin shoot growth in late March. By early April, plants are 5-10 cm tall and are pushing through the leaf litter. Anthesis typically begins during mid-May and continues through early June. Pollination is principally or exclusively by Hymenoptera of the superfamily Apoidea (bees). The corolla shrivels somewhat and falls from the calyx one or two days after pollination, presumably within 24 hours of fertilization. The calyx closes around the developing fruit immediately after corolla abscission. During the next two to four weeks, the calyx and the enclosed nutlets enlarge and mature. The calyx then dehisces by the loss of the upper lip, and the nutlets are released...A different course is followed if fertilization does not occur. The corolla shrivels markedly and may or may not remain united to the calyx. The entire calyx, still open at the mouth, falls leaving the pedicel bare."
Workers at Shorter College are apparently conducting demographic and autecological studies on S. montana. Preliminary results indicate that less than 40 % of the flowers produce mature nutlets. Collins (1976) found that in other species of this group of Scutellaria studied, 76 to 93% of the flowers form nutlets. This lowered rate of fruit production, and the often few-flowered inflorescences, combine to give S. montana a reproductive capacity less than many of its relatives. The nutlets have a smooth exterior and do not appear to be adapted for any means of long-distance dispersal; they most likely fall a short distance (= 5 m) from the parent plant due to explosion of mint capsule. They could be washed downslope by water, or carried by small animals, but have only remote chances of extrapopulation dispersal. However, as Collins (unpublished manuscript) notes, this cannot alone explain its rarity, in that all of its more widespread relatives have virtually identical seed dispersal.
Conditions necessary for germination and establishment are still unknown, although the Marshall Forest population has variously been described as from 500 to 1,300 plants. This may represent actual population fluctuations.
Scutellaria species in the group to which S. montana belongs generally occur at fairly low density, scattered seemingly at random over fairly large areas of forest. Large colonies are seldom found, and individual plants are usually widely spaced and easily distinguishable. S. montana may sometimes occur in tighter colonies than many of its relatives, as indicated by its clumped distribution at Marshall Forest. In the largest Tennessee population (ca. 5,000 individuals), the plants are spaced at approximately 6" intervals (Hawks 1985b), giving a density of 4/sq ft, or ca. 40/sq meter. In the smaller Tennessee populations, however, density is 1 plant per sq meter or less, and individuals can be separated by 50m or more from the nearest S. montana (Bridges 1983, 1984; Bridges and Hawks 1984)
Collins (unpublished manuscript) indicates that S. montana was only known to occur in minimally disturbed sites with a stable habitat. This would indicate it to be a plant of late-successional or climax forests. In Tennessee, some of the sites have clearly younger trees and more recent disturbances than the above would suggest. One site has trees generally 30-40 years old; most sites average trees less than 60 years old. The largest site is in a relatively old (50-60 yrs ?) forest, but is unique in that there had been a gentle ground fire about three years before the discovery of S. montana at the site. While S. montana will not, or has not been observed, to grow in early successional pine stands, it will occupy relatively mature stands with varying degrees of disturbances. Thus it can be considered a mid-to-late successional species which probably persists in, but is not restricted to, mature or climax forests. This is the typical situation for most forest herbs of the region.