Distance to seed sources and land‐use history affect forest development over a long‐term heathland to forest succession

Abstract

AbstractQuestionsIs there a spatial pattern in the community structure (stem densities, species richness and species composition) of trees and shrubs during more than 100 yr of heathland to forest succession? To what extent is community structure influenced by land‐use history and distance to seed sources? Do these effects change in time?LocationA 350‐ha heathland (Nørholm) in southwest Denmark was abandoned in 1895 and left for free succession. Prior to abandonment the heathland was under traditional management for centuries.MethodTrees and shrubs were recorded and measured in ten surveys spanning 91 yr (1921–2012). In the first nine surveys, complete censuses were used, whereas 116 randomly placed plots (10‐m radius) were used in the most recent survey. We used mixed models and different multivariate techniques (non‐metric multidimensional scaling and permutational multivariate ANOVA) to analyse spatio‐temporal patterns in stem densities, species richness and species composition and the effects of land‐use history and distance to seed sources.ResultsTree and shrub densities increased exponentially over time and were consistently lower at longer distance from seed sources. Land‐use history affected the rate of increase in tree densities, with lower encroachment rates at previously cultivated soils. Initially, species richness increased rapidly but leveled off in later successional stages. Richness was marginally higher at areas closer to seed sources, whereas it was not affected by land‐use history. The succession showed a shift from early to mid‐successional species over time; but distance to seed source determined which species were colonizing at early stages.ConclusionDistance to seed source and land‐use history can differentially affect the structure and spatial patterns of developing forest communities. Although both factors had long‐lasting effects on rates of colonization, the spatial patterns of colonization and species composition were mainly determined by distance to seed sources. The importance of distance to seed sources became less over time, suggesting that dispersal is a stronger driver at early stages. After more than a century since abandonment, forest covers <30% of the area, indicating that lack of heathland management did not strongly promote tree colonization at this site.