Mature beech trees (Fagus grandifolia; Fagaceae) are persistently clonal in coves and beech gaps in the Great Smoky Mountains

Abstract

Angiosperms frequently have mixed sexual and asexual reproductive strategies, which can have significant consequences for population and community structure. Many tree species respond to disturbance by vegetative sprouting over sexual reproduction, but the ability to do so varies within and among species and is poorly studied. We tested the hypothesis that root sprouting in Fagus grandifolia is more important in high-elevation beech forests (extreme environmental conditions), relative to lower-elevation cove hardwood forests (optimal environmental conditions), in Great Smoky Mountains National Park. Four cove hardwood and two high-elevation beech gap forests were sampled. Fagus grandifolia trees were tagged, mapped, and genotyped at each site using six nuclear microsatellite loci. A subset of trees was cored to determine minimum ages of identified clonal lineages. Relationships between measures of clonal richness, diameter, forest type, and elevation were compared by nonparametric analyses. Five of six sites were highly dependent on sprouting; one site was entirely dependent on reproduction by seed. Clonal richness did not differ significantly by forest type or elevation, but differed significantly from previously published work. Tree diameter was significant by elevation and significant between the present study and previously published work. The results of this study in the context of previously published work suggest that relatively recent recruits may be more likely to reflect both sexual and asexual strategies, whereas mature F. grandifolia may be more likely to be the result of persistent clonal lineages.