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The ability of tree species to cope with anticipated decrease in water availability is still poorly understood. We evaluated the potential of Norway spruce, Scots pine, European larch, black pine, and Douglas-fir to withstand drought in a drier future climate by analyzing their past growth and physiological responses at a xeric and a mesic site in Central Europe using dendroecological methods. Earlywood, latewood, and total ring width, as well as the δ(13) C and δ(18) O in early- and latewood were measured and statistically related to a multiscalar soil water deficit index from 1961 to 2009. At the xeric site, δ(13) C values of all species were strongly linked to water deficits that lasted longer than 11 months, indicating a long-term cumulative effect on the carbon pool. Trees at the xeric site were particularly sensitive to soil water recharge in the preceding autumn and early spring. The native species European larch and Norway spruce, growing close to their dry distribution limit at the xeric site, were found to be the most vulnerable species to soil water deficits. At the mesic site, summer water availability was critical for all species, whereas water availability prior to the growing season was less important. Trees at the mesic were more vulnerable to water deficits of shorter duration than the xeric site. We conclude that if summers become drier, trees growing on mesic sites will undergo significant growth reductions, whereas at their dry distribution limit in the Alps, tree growth of the highly sensitive spruce and larch may collapse, likely inducing dieback and compromising the provision of ecosystem services. However, the magnitude of these changes will be mediated strongly by soil water recharge in winter and thus water availability at the beginning of the growing season.

Summary1 This paper assesses whether tree-ring patterns found in recently dead mountain pines ( Pinus mugo Turra) infected by Armillaria spp. differ from those infected by Heterobasidion annosum , and determines whether and to what extent tree rings may be used as indicators of tree-decline history (i.e. tree health conditions in relation to disease history) prior to death. 2 Dendroecological and phytopathological analyses were undertaken in the Swiss National Park. The calendar year of death of the standing dead trees was determined by cross-dating ring-width patterns of dead trees to reference chronologies from living trees. This procedure is not, however, exact as there may be multiple intermittent missing rings. 3 A remarkable discrepancy (up to 31 years) was found between the tree-death year estimated through crown condition assessment (i.e. the presence or lack of green needles) and the date of the outermost tree ring (when tree-ring production ceased). New needles may form and existing ones remain green for some years after the cambium at different heights along the stem has ceased activity and no new wood cells are being formed. 4 Ring-patterns in trees infected by Armillaria differ from those in trees infected by H. annosum . All dead trees infected by Armillaria had a slow growth decrease indicating suppression for several decades, and suggesting that Armillaria attacked trees that were already weakened by competition. In contrast, trees infected by H. annosum died over a very short period of time, although they may have been infected a long time previously. Nevertheless H. annosum seems to infect and kill trees directly , whereas Armillaria , at this site, is a secondary pathogen. 5 This study demonstrates that tree rings may be used as indicators of the history of tree decline prior to tree death. However, the history of tree disease is difficult to reconstruct fully, e.g. tree rings do not enable the onset of infection to be dated.

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