Environmental determinants for forest composition development in the Netherlands during the Holocene

Abstract

Assessing the relationship between environmental gradients and plant distributions is an important field of study in ecology, but as in many countries the natural vegetation has been cleared by human activities, this relationship is often challenging to study. Alternatively, the relationship between past environmental gradients and vegetation cover is a possibility that could be assessed but has not yet been thoroughly explored. This study focuses on the Netherlands, which has a rich paleogeographic and palynological database, a prerequisite for a study like this. Past vegetation is assessed based on pollen data compared to abiotic gradients for different time slices during the Holocene. 329 fossil pollen records from the European Pollen Database in Neotoma were used as biotic input and four environmental parameters (distance to the sea, elevation, (modern) average groundwater level and soil substrate type) were used to assess the relationship between environment and vegetation over time. Isopollen maps were created to assess the spatial distribution of pollen types. Principal Component Analysis was applied to assess the ordination of the pollen taxa for all time slices with the environmental parameters plotted passively over them. Variance Partition was then used to quantify the explanatory power of the environmental parameters for every time slice. The results show that for certain plant taxa (e.g. Alnus, Pinus, Betula) during the Holocene, environmental gradients existed, and some changed through time. Together, the environmental parameters explained ~10-30% of the variance in the pollen composition, depending on biostratigraphic zone and whether wetland taxa and/or sites from south Limburg were excluded. The importance of individual environmental parameters changes between biostratigraphic zones, but the environmental parameter associated with the river delta area is dominant during all time slices. During the Subatlantic, the environmental control on the landscape decreased, likely because of increased human influence. This study demonstrates palaeoecological parameters are suitable for assessing environmental control on plant taxa distribution.