Vegetation diversity and stand structure in streamside forests in the south of Ireland

To investigate the nature, diversity and structure of the streamside vegetation, 10 forest sites were selected in the south of Ireland. The vegetation was sampled following the Braun–Blanquet method and gradients in vegetation were examined using belt transects perpendicular to streams. Vegetation relevés were classified using TWINSPAN, which separated five vegetation types: semi-natural oak forest on base-poor soil, conifer plantations, broadleaved stands on base-poor soils, mixed broadleaved–conifer stands and broadleaved stands on base-rich soils. Plant species richness in the broadleaved stands was almost double that of conifer plantations. Plant species richness and total vegetation cover decreased with distance from the stream, which is likely to be the result of reduced levels of light, water and soil nutrients away from the streambank. To reveal the stand structure, all trees and shrubs (diameter ≥ 5 cm) in the relevés were recorded, and the average diameter, density and importance value (structural role) were calculated. Although many introduced species (of which Sitka spruce is the most important) are present in the study sites, native woody species have a greater importance value index (IVI).