Growth responses of Persian walnut (Juglans regia L.) to climate variation along its full elevational range in Kyrgyzstan

Kyrgyzstan features the largest naturally occurring walnut forests in the world. Their high plant biodiversity, including wild relatives to modern-day fruit species such as apple and pear, make them a valuable guardian of genetic diversity. Further, walnut forests have a high economic importance for the country. Climate change, however, poses a major threat to these ecosystems, in particular since rises in temperature are projected that are well above global average. As studies on effects of changing environmental conditions on the growth of walnut are missing, we investigate the climate sensitivity and temporal stability thereof as well as extreme growth responses of walnut along its full elevational gradient in Kyrgyzstan. Whereas we expected to find a shift from water- to temperature-limitation over the elevational gradient, which may move upwards with recent warming, we found walnut growth to be temperature-limited along the entire elevational gradient. In recent decades, negative correlations between the drought index SPEI and tree growth, however, weakened. An up until now low importance of drought stress for walnut growth is also substantiated by a pointer-year analysis. Overall, our results show that walnut growth is already affected by climate change, though imminent risks of drought-induced vitality loss seem still low. With ongoing climate change, this may, however, rapidly change.