Mountain stewartia (Stewartia ovata), is endemic to Great Smoky Mountains National Park (GSMP) and eastern Tennessee. This understory woody plant is known for its ornamental inflorescences in mid-summer and its scarcity across its native range. Due to its rarity, population estimates and range descriptions are limited and longstanding. Aside from physical descriptions, little information is available regarding its habitat requirements. To better assess mountain stewartia’s habitat requirements and populations throughout the park and eastern Tennessee, we first located and inventoried five populations inside GSMP and five populations outside the park on private lands. For each population inventoried, stewartia stems were counted and total heights and root-collar diameters were recorded. Soils were identified and collected and assessed for overall pH and micronutrient levels. Overstory, midstory, and understory woody and herbaceous plants were recorded and measured to determine forest composition. In addition, overstory canopy density and full photosynthetically active radiation (PAR), percent slope, aspect, elevation, and distance from streams were also measured. These variables were quantified as a preliminary step in determining whether stewartia is rare because of a unique or altered habitat, limited sexual reproduction, poor dispersal, or a combination of these factors.
Results/Conclusions
Stewartia averaged 7.40 (± 1.08) stems per population across study sites. Soils were highly permeable, well-drained, cobbly loams associated with steep slopes and higher elevations and were strongly acidic, with low concentrations of calcium, magnesium, phosphorus, and potassium. Overstory trees were comprised predominantly of sourwood (Oxydendrum arboreum), eastern hemlock (Tsuga canadensis), white oak (Quercus alba), eastern white pine (Pinus strobus), red maple (Acer rubrum), and mockernut hickory (Carya tomentosa). These overstoy canopies were dense, resulting in 7.05 (± 1.41) % of full PAR. The midstory and understory were dominated by eastern hemlock, eastern white pine, and red maple. Stand-level conditions in extant stewartia populations suggested similarities in soil pH, nutrient levels, drainage, and overstory composition and structure, and PAR levels. Certain conditions in stewartia sites were unique in the region, suggesting that habitat may be important in limiting populations along with other factors. Eastern hemlock was a species common to all sites found to support stewartia, and the ongoing loss of this species to hemlock woolly adelgid (Adelges tsugae), may have uncertain implications for extant stewartia populations. In addition, investigations into stewartia reproductive ecology, dispersal mechanisms, associations, and other key habitat requirements will be necessary to insure conservation of this species.