Composition and Structure of Tsuga caroliniana Engelm. Communities in the Southern Appalachian Mountains of Western North Carolina

Abstract

Tsuga caroliniana (Carolina Hemlock) is a species endemic to the southern Appalachian Mountains. Extant populations are under threat from the spread of introduced Adelges tsugae (Hemlock Woolly Adelgid), and information necessary to inform Carolina Hemlock conservation and future restoration efforts is limited. Our research characterized the structure and composition of Carolina Hemlock communities in the middle of its geographic range. We identified 5 sites where Carolina Hemlock comprised a major component of the stand. We collected data on structure, composition, and physiography in four 0.05-ha plots at each site. We quantified density and diversity of the overstory (≥5 cm dbh) and regeneration (<5 cm dbh) layers and used non-metric multidimensional scaling (NMS) to characterize species composition. At all but 1 site, Carolina Hemlock possessed the greatest importance value. Aspect, basal area, and species diversity varied only slightly among the sites. Overstory species composition was distinct at each site, while that of the regeneration layer was similar. Only 3% of the stems in the regeneration layer were Carolina Hemlock, with the seedling layer dominated by Acer (maple) species. Consequently, overstory mortality following disturbance will likely result in the recruitment of shade-tolerant species, maples in particular, which would homogenize the composition of these 5 distinct Carolina Hemlock communities.