Mixed forest suffered less drought stress than pure forest in southern Siberia

Abstract

Hotter droughts are becoming a major threat to forest growth in water-limited regions. Species interactions have long been acknowledged as an important component modulating ecosystem functions, including mediating their vulnerability to climate-related stresses. However, quantifying the impact of species interactions on forest growth in response to drought remains a challenge. Using the tree ring data of two species in two pure forests and two coniferous and broad-leaved mixed forests with different degrees of mingling in southern Siberia within the period of 1960–2017, we found that mixed forests with higher mingling have a higher ability to withstand the effect of extreme drought events, which is especially beneficial to the resistance and resilience of broad-leaved trees. Larch trees showed a remarkable consistency in their resistance and resilience to extreme drought events in both pure and mixed stands, suggesting their ability to promote the growth of neighboring white birch without reducing their own growth. The growth of white birch trees was enhanced in mixed forests and showed a significant trend of increasing resistance and resilience with increasing mingling. Our results provide further evidence of a decreasing duration of the legacy effect with increasing mingling for both coniferous and broad-leaved trees, which might explain the improved tolerance to drought of trees in mixed forests compared to those in pure forests in water-limited hemiboreal southern Siberia. Our study implies that changes in forest structure might help forests respond to hotter droughts in water-limited regions.