Microsites Supporting Endemic Populations of Mountain Stewartia (Stewartia ovata) in East Tennessee

Abstract

Mountain stewartia (Stewartia ovata) is the only member of the family Theaceae endemic to Tennessee. Apart from its physical description and rarity, little is known about this woody understory species. Accounts of stewartia populations and range descriptions are longstanding, but microsite descriptions are limited in detail. We quantified microsites supporting populations of stewartia across East Tennessee as a first step in determining whether stewartia is rare because of rare or altered habitat, limited sexual reproduction, poor dispersal, or a combination of these factors. Five populations of stewartia averaging 7.40 ± 1.08 stems per population were inventoried across four East Tennessee counties. Soils on all sites were strongly acidic, highly permeable, well-drained, cobbly loams associated with steep slopes and higher elevations and were low in phosphorus, potassium, calcium, and magnesium. A dense overstory comprised 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) resulted in 7.05% ± 1.41% of full photosynthetically active radiation (PAR). The midstory and understory were dominated by eastern white pine, red maple, and eastern hemlock. Quantification of stand-level conditions in extant stewartia populations suggested similarities in soil pH, nutrient levels, drainage, overstory composition and structure, and PAR levels. Certain conditions in stewartia sites were unique in the region, suggesting that habitat may limit populations along with other factors. Further investigations of stewartia reproductive ecology, dispersal, and habitat requirements will be key to conserving this species.