The ecological and biogeochemical importance of snow cover for temperate forest ecosystems
Final Report Abstract
Climate is changing rapidly and understanding the response of ecosystems to climate change is vital for human well‐being. Climate change over winter is particularly strong, but largely understudied despite being more uncertain in its ecological impact as reduced snow cover can potentially even lead to ‘colder soils in a warmer world’ (Peter Groffmann) in regions with seasonal snow cover. For European beech (Fagus sylvatica L.), the major forest tree in European temperate deciduous forests, growth is commonly expected to decline due to increasing summer drought exposition. However, winter cold sensitivity is largely unexplored. Here, we investigated the climate sensitivity of biogeochemical cycles, plant species composition, and forest growth dynamics across spatial scales using field observations, a large‐scale gradient‐design field experiment, and dedicated lab experiments in order to optimize external and internal validity of our conclusions. A dendroecological study along a large winter temperature gradient (ΔT = 4 K across 500 km) from central to cold‐marginal beech populations was conducted to identify gradual changes in summer drought and winter cold sensitivity in tree growth. Towards the cold distribution margin, the influence of drought on tree growth gradually decreased, while growth reductions were increasingly related to winter cold due to harsher winter climate. Although regional climate drives growth of adult forest trees, local factors, such as site‐specific edaphic conditions, might control plants in the forest understory. Across the same gradient, we found that edaphic conditions explained the spatial turnover in the forest understory composition more than climate, which might moderate direct climate change impacts on the forest understory composition. However, edaphic conditions, forest structure, and climate are linked by triangular interactions. Thus, climate change might still indirectly affect the forest vegetation dynamics. The field experiment simulated the influence of winter climate change on forest ecosystems by snow cover and soil temperature manipulations and indicated that soil cooling and decreased root nutrient uptake indirectly reduce growth of adult forest trees. Moreover, this study indicated uniform ecological sensitivity to soil temperature changes across the winter temperature gradient, which motivates upscaling from local winter climate change studies to the regional scale. Working directly with adult trees has rarely been achieved in manipulation experiments but proved important, as we further showed that juvenile trees overestimate the nitrogen acquisition responses of mature trees to winter temperature variation. The highly controlled lab experiment supported the insights from the field experiment. Previously cold sites which will lose their protective snow cover during climate change appear most vulnerable to increasing soil freeze‐thaw frequency and magnitude, resulting in strong shifts in nitrogen and phosphorus release. In nutrient poor European beech forests of the studied Pleistocene lowlands, nutrients released over winter may be leached out, potentially inducing reduced plant growth rates in the following growing season. In conclusion, this project highlighted that multidisciplinary research is crucial to advance the understanding of ecological interactions in forest ecosystems under changing climate scenarios. Here, a winter climate change experiment, where site‐representative target trees were selected by means of dendroecology, contributed to a mechanistic understanding of winter cold sensitivity in forest growth dynamics. The dendroecological investigations put the findings in a broader temporal and spatial context by describing local climate sensitivity of tree growth on different spatial scales. Dedicated lab experiments further established causal relationships. Taken together, the study suggests that winter climate change affects the biogeochemistry and ecology of temperate forest ecosystems, with strongest responses in (formerly) coldest regions. TV report „Was macht der Klimawandel mit den Bäumen“ at NDR Nordmagazin May 2017.
Publications
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(2018) Temperate Deciduous Forests in Europe Under Climate Change: Impacts Across Spatial Scales and Sensitivity to Winter Soil Temperature Variation. Doctoral Thesis, University of Greifswald
Weigel R.
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(2018) Winter matters: Sensitivity to winter climate and cold events increases towards the cold distribution margin of European beech (Fagus sylvatica L.). Journal of Biogeography 45: 2779‐2790
Weigel R, Muffler L, Klisz M, Kreyling J, van der Maaten‐Theunissen M, Wilmking M, van der Maaten E
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(2019) Forest understory vegetation is more related to soil than to climate towards the cold distribution margin of European beech. Journal of Vegetation Science 30:756‐755
Weigel R, Gilles J, Manthey M, Klisz M, Kreyling J
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(2020) Lowest drought sensitivity and decreasing growth synchrony towards the dry distribution margin of European beech. Journal of Biogeography
Muffler L, Klisz M, Kreyling J, van der Maaten E, Wilmking M, van der Maaten‐ Theunissen M
