Topographically induced variation of microclimatic and soil conditions drives ground vegetation diversity in managed Scots pine stands on inland dunes

Abstract

The goal of this study was to determine the topographically induced pattern of ground vegetation in managed Scots pine (Pinus sylvestris) stands on inland dunes and to link the pattern to the spatial variation of environmental agents (microclimatic and soil conditions). The study was conducted in the Toruń Basin (N. Poland), which is located in one of the biggest inland dune fields of the European sand belt. We investigated ground vegetation in 151 plots situated in 3 topographical variants (intra-dune depressions, north- and south-facing dune slopes). Environmental variables were examined in the 3 studied relief positions both with indirect (Ellenberg Indicator Values – EIVs) and direct approaches (measurements of air temperature and humidity as well as soil temperature and moisture). The relationship between the pattern of species composition and environmental controls was investigated using redundancy analysis (RDA).We evaluated the persistence of topographic patterns under the potentially homogenizing influence of forest plantations by sampling pine stands at different stages of growth. Intra-dune depressions were revealed as positions of the highest richness in herbaceous species. This was primarily linked to soil fertility and secondarily to moisture, which were both higher in these positions than on both slope aspects. The affinity of the species richness to low-situated locations was the strongest in mid age classes of pine stands, where stress conditions, resulting mainly from shadowing, were of the highest importance for understory throughout the stand development. However, the results showed that finally in old-growth stands, typical herbaceous species appeared for each of the studied topographical positions. Our study showed that intra-dune depressions could be used in forest management to introduce admixtures of broadleaved species into extensive pine mono-stands. This potentially could increase ecological stability of pine stands growing on inland dunes as well as support forest productivity of such ecosystems.