Effects of stand-level and landscape factors on understorey plant community traits in broad-leaved forest of the boreo-nemoral zone in Latvia

Knowledge of the limiting processes shaping the composition of plant communities of woodland is important in conservation of biological diversity. The aim of our study was to examine the effect of stand-level factors (soil and canopy composition, age and area) and landscape factors (fragmentation of broad-leaved forest, distance to a historical manor house, and past history) on plant community trait composition in broad-leaved forest. We hypothesized that the plant functional community is shaped by both dispersal filtering due to landscape factors and by environmental characteristics. We recorded all vascular plants, described canopy composition and estimated soil characteristics in 44 randomly chosen broad-leaved stands in Latvia. Relationships between plant community traits and potential factors were assessed using PCA and multivariate regression analysis. Interrelationship of richer topsoil fertility and admixture of broad-leaved tree species other than Q. robur was associated with greater abundance of nemoral species and hemicryptophytes. The invasion of Picea abies into the canopy was associated with poor topsoil fertility and acidified soil, likely due to poor litter quality, and with greater number of boreal species and geophytes in the herb layer. The results suggested a weak and contradictory effect of landscape structure and history on the forest plant community traits, maybe because the long-term history of afforestation around manors and spatio-temporal connectivity to ancient forests had resolved these effects.