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Increasing the potential of economically valuable tree species to survive drought

Final Report Summary - INPUT-DROUGHT (Increasing the potential of economically valuable tree species to survive drought)

- Increasing the potential of economically valuable tree species to survive drought.
(FP7-PEOPLE-2010-IEF) Marie Curie Fellow: Britta Eilmann
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Future forests have to provide sufficient amounts of high quality timber due to the increasing demand. However, decreasing water availability caused by global climate change is expected to substantially reduce forest stability and productivity. Timely action is needed to mitigate these negative effects of climate change on forests given the long live span and thus the long rotation periods of trees. Moving provenances (populations of a species which are genetically adapted to the site conditions at the place of origin), from dryer environments in the south toward north to plant them on moderate sites in Europe would mimic long-term migration. This might be a promising strategy to guarantee forest stability under rapid climate change. Alternatively, highly productive non-native species could be planted to guarantee forest productivity. Their yield could be further increased by - also here - selecting the optimal provenance for given site conditions. However, the suitability of these provenances for plantation under moderate conditions have to be tested and provenance trials form an excellent basis to do so.
In this study we focused on two economically valuable species: (i) European beech (Fagus sylvatica L.), a native European species, is highly appreciated by foresters and wood industry due to its favourable wood-technological properties. However, beech is threatened by climate change due to its sensitivity to drought. (ii) Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), a non-native species in Europe, was introduced from North West America and is valued for its high productivity rates. Provenances trials of both species were used in this study to compare the performance of different provenances in terms of productivity and drought-tolerance.
In a first experiment the performance of southern beech provenances which were transferred to a moderate site in the Netherlands was compared with the performance of northern provenances. We did a multi-proxy analysis focussing not only on tree growth and tree survival but analysing also changes in the wood-cell structure in beech. Due to a strong link between the cell structure and its function, namely water transport from the roots to the leaves, it is possible to evaluate which water-conducting system is most suitable to withstand drought events and estimate the metabolic consequences of drought years and ultimately their effect on tree growth and vitality. We used a novel automatic image-analysis tool (ROXAS) allowing the time-efficient analysis of a large quantity of wood-anatomical data. The results revealed one outstanding beech provenance originating from the south, which showed cell features that enable efficient water transport and which showed consistent better growth than the other provenances combined with low mortality rates. Strikingly, this provenance maintained its high growth level and cell size even in the drought year 2003, pointing to a higher tolerance towards drought compared to the other provenances.
In a second experiment we analysed how provenances originating from moderate sites in the North, grow on dry sites. The results proved, that beech provenances have the ability to adjust plastically to exacerbating site conditions since northern provenances showing a similar level of increment as the local provenance. Thus the models on future distribution of beech might be too pessimistic since the ability of beech to plastically respond to drought was neglected until now.
In a third experiment we analysed the water transport efficiency and safety of beech clones with a different wood structure, i.e. smaller versus larger cells in a drying-out experiment to better understand the cause for the high sensitivity of beech towards drought. During the experiment the spatial distribution of water-volume flow and cavitation (cell embolism) was monitored in vivo using NMRi (Nuclear Magnetic Resonance imaging). Under well-watered conditions the speed of water transport clearly differed between the two clones. During the drying-out experiment, the spatial distribution of water loss was similar for both clones but the speed of water loss and the reduction in water flow greatly differ between the clones. These results prove the strong relationship between the wood structure and the functioning of the water conducting system in trees and form an excellent basis for eco-physiological modeling approaches.
To scrutinise if past recommendations on Douglas-fir provenance selection for plantation in Europe are still valid under exacerbating climate conditions we tested the performance of 18 coastal Douglas-fir provenances ranging from British Columbia in the North to Oregon in the South and planted in a Dutch provenance trial. Specifically we looked at seedling survival, yield, wood quality, and drought tolerance. We found a clear trends in productivity and drought tolerance related to the origin of the provenances: Productivity increased from southern towards northern provenances while drought tolerance increased towards South. Therefore a coeval maximisation of productivity and drought tolerance is not possible. However, the results also showed that promising provenances originate from the Olympic Peninsula (Washington) since they were very productive and possess a high potential to cope with drought.
Based on our results we are able to give recommendation on suitable beech and Douglas fir provenances to be planted to mitigate the effect of exacerbating climate conditions. Foresters are urgently seeking for information about suitable material for plantations to adjust forest-management systems to the projected climate change. In case of beech our results proved that “assisted migration” might be a tool to guarantee the stability and productivity of future beech stands since one provenance from the south showed an excellent performance on the moderate site even under drought. The NMRi experiment gain new insights into the relationship between wood-anatomical properties, water-transport capacities and resistance to drought.