Silvicultural climatic turning point for European beech and sessile oak in Western Europe derived from national forest inventories
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Forests of temperate Europe are climate sensitive ecosystems, and the current balance between the tree species will shift as climate becomes warmer and potentially drier. Especially changes in the dominant species have a strong impact on forest ecosystems because they fundamentally change life conditions of plants and animals living in the forest. Mette et al. (2013) introduced the climatic turning point (CTP) as a concept that marks the climatic conditions where such a change in species dominance is expected to occur. While they modelled the CTP for European beech (Fagus sylvatica) and sessile oak (Quercus petraea) from environmentally sensitive forest growth models, this study determined the CTP between beech and oak from national forest inventories in Western Europe. We ask (1) under which climate conditions the inventory-based CTP occurs, (2) whether it is modified by soil type and (3) how it differs from other CTP references like the Ellenberg quotient (Ellenberg, 1963). The CTP from beech to oak occurred approximately at mean annual temperatures above 8–9 °C if annual precipitation was below 600 mm and rose to 11–12 °C for annual precipitation exceeding 900 mm. This relation was strongly modified by soil type. Compared to Ellenberg (1963) and Mette et al. (2013), oak replaced beech at far more moderate climatic conditions (EQ 20–30). This can be attributed to the silvicultural history of forest stands: the inventory-based CTP signal carries the century old anthropogenic preference for oak. We expand the CTP concept that was until now based on natural competition by a “silvicultural” CTP that is contained in large-scale inventory data. It thereby implicitly incorporates the question how silviculture and social-cultural values impact the balance between species. Climate change projections indeed suggested that large parts of Western Europe will cross the silvicultural CTP.