Softwood for the future

Climate models predict an ongoing increase in air temperature along with changes in precipitation amounts and patterns. High temperatures trigger drought periods, and heat waves - like in 2003 - are expected to occur every few years. Eastern Austria is a dry region with precipitation sums of 500 to 700 mm per year. Therefore, water availability is one of the most crucial factors for forest stability in Eastern Austria. Negative effects of extreme climatic events act not only within the single year when the climate extreme takesk place, but have an impact on tree vigour and fitness over a much longer time span. For example, the Central European summer drought period in 2003 had significant effects on needle and leaf volume along with a decreased annual increment for more than four years. Density is the main predictor of wood quality. Increased wood density increases wood quality as well as the price of the logs. Therefore, extreme climates do not only affect forest stability, but also the income and financial risk of forest owners, as well as potential subsidies of national governments and the European Union. The climatic distribution limits of tree species are not exclusively determined by average measures of temperature and precipitation but rather by climate extremes. Due to the expected changes in climate, forest planning and management need to consider drought resistance as a key factor for the selection of tree species and seed provenances. In the present project we aim to assess the tree response to past drought events by ring width and x-ray densitometric measurements. In particular, we are interested in the drought-response of the economically important conifer species Norway spruce, European larch, Silver fir, and Douglas fir. Intra-specific variation of drought resistance will be analyzed. The question, if tree breeding can use this variation to adapt tree population to future climates will be answered. The dendroclimatological analysis will be carried out on trees from various provenance experiments, e.g. experiments where trees with different seed origin were planted. These experiments are located within the eastern part of Austria, namely, the forest growth region 8.1 (Pannonic low- and hill lands), which is characterized by high temperatures and low precipitation and where severe drought periods have already been observed in the past. Learning from how the different species and provenances reacted to drought periods of the past two decades will help us to understand the species` climatic limits and to develop adaptation options for vital forests under future climate.

Climate models predict an ongoing increase in air temperature along with changes in precipitation amounts and patterns. High temperatures trigger drought periods, and heat waves like 2003, 2014 and 2015 are expected to occur every few years. This leads to higher stress for the trees due to high temperature and drought in the warm and dry regions of eastern Austria. Negative effects of climatic extreme events can affect forests directly (storms, forest fire, or periods with reduced annual increment evoked for example by drought) or indirectly (a higher susceptibility to various pests and diseases e.g. bark beetles, fungi). Such indirect effects were apparent, for example, on black pines in the year 2015, where the interaction of severe drought and a fungi (Diplodia pinea) resulted into a massive regional forest dieback. Therefore, extreme climates do not only affect forest stability, but also the income and financial risk of forest owners. Moreover, extreme events bias the carbon budget on regional and global scale.Understanding drought sensitivity of tree species and its intra-specific variation is required to estimate the effects of climate change on forest productivity, carbon sequestration and tree mortality as well as to develop adaptive forest management measures. Here, we studied the variation of drought reaction of 12 softwood-species from which various provenances were planted on trial sites in the drought prone eastern Austria. Tree-ring and X-ray densitometry data were used to generate early- and latewood measures for ring width and wood density. Moreover, the drought reaction of species and provenances within six distinct drought events between 1970 and 2011, as identified by the standardized precipitation index, was determined by different drought response measures. The mean reaction of species and provenances to drought events was strongly affected by the seasonal occurrence of the drought: a short, strong drought at the beginning of the growing season resulted in growth reductions up to 50%, while droughts at the end of the growing season did not affect annual increment. Wood properties and drought response measures showed significant variation among species as well as among provenances.