Enhanced sprout-regeneration offsets warming-induced forest mortality through shortening the generation time in semiarid birch forest

Warming-induced mortality and a decline in regeneration potential have recently been observed in semiarid forests. To understand future forest dynamics, studies have begun to examine the long-term resilience of semiarid forests against climate change. Previous research has documented a relatively high resilience through seedling production for patchy coniferous forests at the arid timberline compared to continuous and arid tree line forests. However, it remains unclear whether broad-leaved forests in semiarid regions share the same pattern and how they work. In this study, we observed a similar nonlinear pattern in forest resilience along a local aridity gradient by reconstructing the regeneration history and investigating post-mortality regeneration in white birch dominated (Betula platyphylla) forests in semiarid Inner Asia. Changes in regeneration modes from seedling to sprout production accelerated the white birch regeneration process and speeded up tree replacement. High competition from abundant recruits enhanced both forest resilience and resistance to climate change in arid timberline forests. However, only weak resilience was observed in birch forests at the arid tree line, which stopped regeneration and meant that old trees dominated the age structure. This might increase the risk of hydraulic failure. Our results implied that the decline in regeneration potential was not consistent in semiarid regions. Although forest mortality increased along with aridity, some broad-leaved forests at the arid timberline have a high resilience because they generate abundant sprouts to compensate for the losses from forest mortality. This study shows that a similar resilience pattern occurs under the impact of climate change and that various resilience mechanisms are affected by the different biological features of coniferous and broad-leaved forests in Inner Asia, which have important implications for future forest dynamics in semiarid regions and provide scientific background for managing this vulnerable forest and important insights into persistence of forests in semiarid Inner Asia.