Drought dimensions impact birch resistance and resilience and their determining factors across semiarid forests of northern China

Tree growth in forests is affected independently or jointly by drought dimensions, namely severity, timing, and duration, making the accurate modeling predictions a formidable challenge, and it still remains uncertain how trees respond to multiple dimensions of drought. Here, we quantified the dynamic response of tree growth (evaluated by resistance and resilience) to different dimensions of droughts, and their determined factors, using tree-ring data of 320 trees in 15 birch (Betula platyphylla) forests from semiarid regions across northern China, in conjunction with environmental and biological data. Our results showed that trees had the highest resistance and resilience to extreme droughts occurring in wet seasons, and had the lowest resistance and resilience to extreme droughts occurring in both dry and wet seasons (DS+WS). Surprisingly, we found a novel result that the negative effects of continuous droughts were not always more impactful than those of single droughts. Trees had similar resistance to different durations of DS+WS droughts, and showed no difference in tree resilience between single and continuous droughts when drought severity increased. Tree resistance and resilience to each dimension of droughts showed robust relationships with climatic and soil factors, but were driven by different biological traits. Tall trees with drought-sensitive leaves were the most vulnerable to droughts in dry seasons, but older trees were less resistant to droughts in wet seasons. This study highlights that multiple drought dimensions are crucial factors determining drought impacts on tree resistance and resilience, which may have a wide range of implications for predictions and uncertainty assessments of tree growth and forest management in semiarid regions.