Environmental Correlates to Population Structure and Health of the Rare Piratebush (Buckleya distichophylla) within Poor Mountain Natural Area Preserve, Virginia

Abstract

Piratebush (Buckleya distichophylla, Santalaceae) is a dioecious, hemi-parasitic shrub endemic to the Blue Ridge Ecoregion of the Appalachian Mountains. The Poor Mountain Natural Area Preserve (PMNAP) in southwestern Virginia protects the densest known population of this rare plant. Permanent transects were set within this natural area to measure population density, size-class structure and health indicators, and to analyze their relationship to ecological parameters. Within PMNAP, there were 9 ± 2 piratebush per 100 m2 of forest floor with a mean size of 4 ± 1 stems of 1.9 ± 0.6 cm diameter at ground height. Individual shrubs grew across a broad range of aspects, slopes (2–50%), and canopy cover (0–100%), exhibiting minimal crown death and a wide range of foliar color value. Weighted size class structure distribution was positively skewed, with low indication of recent seedling recruitment. Observed adventitious vegetative regeneration may mask the frequency of genetically distinct individuals, and indicate less genetic diversity within this population. Weighted size class was positively correlated to forest canopy cover (P < 0.001) and southerly aspect (P = 0.071). Foliar color value was positively correlated with canopy openness (P < 0.001) but neither weighted size class nor plant vigor. This study indicates that successful sexual reproduction within this piratebush population may be rare, and establishes a detailed baseline assessment of the largest extant piratebush population, enabling future study of factors relevant to the long-term viability of this species.