Influence of historical, geographical and environmental variables on understorey composition and richness in Danish forests

Question: What is the relative influence of forest continuity, environmental differences and geographical context on vegetation and species richness in ancient and recent forests? Location: Himmerland and Hornsherred in Denmark. Methods: Lists of forest species from deciduous forests were subjected to CCA with variation partitioning to quantify the relative amount of variation in species composition attributable to historical, present geographical and environmental variables. GLM was used to estimate the importance of the variables to species richness. Results: The importance of temporal forest continuity in one region was negligible but was considerable in the other. The variation in species composition explained by geographical, environmental and historical variables showed little overlap in both regions, particularly at the fine scale. Conclusions: This paper does not support the idea that differences in the flora between ancient and recent forests is mainly caused by environmental differences. Furthermore, species richness seemed unaffected by isolation and forest connectivity. Nomenclature: Hansen (1981). Abbreviations: GLM = Generalized linear model; TVE = Total variation explained.