Relations between density of rhododendron thickets and diversity of riparian forests

Abstract

Rosebay rhododendron ( Rhododendron maximum L.) is increasing its range and abundance in understories of southern Appalachian forests, reducing species richness, and altering patterns of succession. This study characterized the density and biomass attributes of R. maximum thickets and examined their effects on plant species richness, percent cover, and regeneration patterns within a southern Appalachian riparian ecosystem. R. maximum reached densities exceeding 17,000 stems ha −1 with biomass reaching 34 Mg ha −1. Species richness and percent cover in the regeneration layer were inversely related to R. maximum thicket density in both Spring and Fall samplings. On average, 6 plant species were found on plots with high R. maximum stem density as compared to 26 species found on plots with lower stem density. The regeneration layer was dominated by R. maximum with only low numbers of tree species present. Both woody and herbaceous species regenerated poorly under the dense canopy of these thickets. Based on the age of cut stems, R. maximum became increasingly dominant in the understory of Wine Spring Creek over the last three decades. Its proliferation is altering the richness of riparian forests and changing historical patterns of community succession.