The ecological and biogeochemical importance of snow cover for temperate forest ecosystems

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Climate warming in central Europe is strongest over winter. Less snow, however, can potentially counteract increasing soil temperature. Winter is generally a crucial driver of ecology and biogeochemistry in temperate forests. Effects of altered snow cover and more variable soil temperatures therefore require scientific attention for a better understanding of climate impacts.In climate change experiments (1) process-based understanding and (2) realism of conditions allowing for sound up-scaling and generalization are sought. Therefore, I propose detailed laboratory trials aiming at the identification of the relevant facets, i.e. magnitude, duration, abruptness, or frequency of frost, for ecological and biogeochemical processes. In addition, I propose novel snow manipulation experiments in mature forests, replicated along a gradient of winter conditions, for up-scaling and generalizations.Snow-out shelters and insulation treatments are novel techniques which allow for the study of alterations in snow cover due to altered insulation of the surface without physical disturbance or alterations of water and nutrient input. This field experiment will include the response of mature trees, a feature rarely achieved in manipulation experiments. Response parameters will provide broad and general results by covering a multitude of ecological and biogeochemical processes such as growth of mature and juvenile trees, tree regeneration, understory species composition, root dynamics, decomposition, mineralization, nitrogen cycling, and trace gas fluxes. This field experiment is intended as a platform for interdisciplinary studies, cooperation partners interested in additional processes will be invited to join.Trials in controlled-environment chambers will focus on two key parameters, i.e. germination/ establishment of the dominant tree species (Fagus sylvatica) and mineralization. These trials will aim at the identification of the ecologically relevant facets of winter temperature regimes. This knowledge is important for the extrapolation of effects to future conditions. Dominant tree species are key in the adaptation of forest ecosystems to altered environments. They harbor considerable intra-specific phenotypic and genetic variability within and among populations in their species ranges. Local adaptations to winter conditions and, generally, plasticity within and among populations will therefore be studied in both, the laboratory and the field experiments.Taken together, the proposed experiments will improve the understanding of winter climate impacts in ecology and biogeochemistry. Gathering such information under very controlled conditions allowing for process-understanding and under field conditions at several sites allowing for generalizations at the landscape scale is relevant for improving coupled atmosphere-biosphere models as well as proactive management of climate change.