Increasing Winter Temperatures Stimulate Scots Pine Growth in the North German Lowlands Despite Stationary Sensitivity to Summer Drought

Abstract

More than half of the forest area of the North German Lowlands is stocked with Scots pine-dominated forests, mostly plantations. Climate change suggests a declining suitability of Europe’s temperate zone for conifer plantations, but only a few studies have examined the long-term growth trends of Scots pine in relation to environmental and site factors in this region. We studied the radial growth patterns of Scots pine over the last 60 years at ten sites along a precipitation gradient (830–530 mm mean annual precipitation) from an oceanic to a subcontinental climate, analyzing the spatial and temporal variability of the climate sensitivity of growth to identify the main climatic factors influencing pine growth across this gradient, which covers a large part of the species’ tolerated precipitation range. Annual radial increment was sensitive to late-winter temperatures (February, March) and summer drought and heat (June–August), with sensitivity increasing from the oceanic to the drier continental sites. Warmer late-winter periods apparently have stimulated growth during the last decades, while the sensitivity to summer-drought has remained fairly stable. Until recently, the negative impact of warming summers on growth has been compensated by the positive effect of late-winter warming, resulting in stable (or increasing) growth trends. However, our comparison of the climate sensitivity across sites suggests that the drought effect compensation through winter warming will in future be limited by increasing drought exposure. Thus, future productivity declines are likely in the northern German lowlands despite warming winters, discouraging large-scale pine plantations in the face of climate warming.