Drought limits growth and hydraulic capacity of two ecologically and economically important tree species in the Lesser Caucasus

Global climate change is expected to strongly impact the biodiverse forest ecosystems in the mountain forests of Armenia. It is still uncertain how climate variability and especially extreme drought events affect the two ecologically and economically important tree species, oak (Quercus macranthera Fisch. & C. A. Mey. ex Hohen) and beech (Fagus orientalis Lipsky). However, this is crucial for designing suitable management practices and guiding future restoration efforts. Here, we investigated the overall climate sensitivity and response to extreme climate events of 14 oak and 22 beech trees from the Tavush province, north-eastern Armenia, based on tree-ring and vessel-related parameters for the period 1950 – 2011. We found that drought conditions mostly limit oak growth during spring, while water availability during summer is most important to beech growth, which is consistent with their wood anatomical characteristics. Climate-growth relationships for both species were not stable over the investigated period and indicated increasing growth sensitivity to water availability in the last decades. This trend was more pronounced for beech than for oak. During extreme dry years, annual growth increment and hydraulic conductivity of both species were significantly reduced but appeared to recover within the following two years. We found that both species can tolerate extreme drought conditions and should therefore be considered for future reforestation efforts. However, as the timing, frequency and intensity of droughts are expected to change in the future, further assessment and monitoring of these two important tree species is needed.