Effect of topography and deforestation on regular variation of soils on inland dunes in the Toruń Basin (N Poland)

Up till now, the effect of topography on soils has usually been studied in mountainous areas, and any reference to relatively small-scale lowland landforms such as inland dunes has not been thus far recognized in any great detail. We investigated the effect of land relief on morphology and the properties of soils in a comparative study covering two ecosystem types (a production forest and a naturally revegetated deforested area) at the Toruń artillery training ground, which is situated in Northern Poland. The objectives of this study were to: 1) compare the morphology and properties of soils with regard to topography on inland dunes at the Toruń military area and to 2) show the modifying impact of deforestation on the effect of land relief on dune soils. In each investigated ecosystem variant, the pedological studies were conducted in two representative catenas; each of them was formed by soils situated in three topographical positions (north-facing slope, south-facing slope, and intra-dune depression). To indicate how the investigated pedons are ordered by soil properties, we applied the principal component analysis (PCA) in the research. Our study showed that regardless of ecosystem type, pedons taken from depressions clearly differed from soils located on both slope aspects, as the soils taken from lower areas form “hot spots” of distinctly higher moisture and fertility in landscapes which are normally dry and poor in nutrients, which is typical of inland dunes. Soils from north-facing slopes, in comparison to soils from south-facing slopes, were characterized by lower temperatures and pH values, higher moisture and stocks of nutrients in O horizons, as well as being more podzolized. However, in the mineral soil layer of 0-100 cm stocks of nutrients were higher in soils from south-facing slopes, which was explained by their lower leaching intensity by acid solutions. The magnitude of the impact of deforestation on the properties of dune soils was found to be strictly related to position in relief. In general, deforestation caused an increase of the differences between soils of the three topographical positions studied; however, this primarily resulted from the strongest influence of forest removal stated for south-facing slopes, while soils located both on north-facing slopes and in depressions were relatively unchanged by deforestation. The topographically-induced differentiation of soils on inland dunes shown in this study can be applied by practices (e.g. foresters, restoration ecologists) in activities to increase the biodiversity of inland dune ecosystems as well as in land restoration (e.g. in dune fixation by vegetation).