Site-specific growth-climate relationships of a widespread coniferous species across mountain areas

Abstract

The prevailing framework for evaluating the ecological responses of a species to climate change assumes the future conditions can be predicted based on spatial variations of this species' performance along climatic gradients. However, such growth-climate relationships for trees may be complicated in high-elevation mountain regions with rugged terrain, especially in semi-arid areas. Here, we investigated the climate sensitivity of a keystone subalpine coniferous species, Qinghai spruce (Picea crassifolia Kom.), using ten standard tree-ring width chronologies (STD) along the temperature and precipitation gradients of the Qilian Mountains. Based on their hydrothermal conditions, the ten sampling sites were classified into two climatic clusters. In warmer and drier conditions (Cluster 1), STD correlated with summer mean temperature negatively, but showed a significant positive correlation with summer precipitation, suggesting trees experienced significant drought stress. The relationships were the opposite at the sites with cooler and moister conditions (Cluster 2) that temperature acted as a limiting factor for tree growth. As the distribution of sites from the two clusters overlapped, the climate sensitivity of Qinghai spruce did not align with the northwest-southeast temperature and meridional precipitation gradients that were widely employed in previous studies. Our results highlight the importance of local climate effects on trees’ responses to climate changes, offering an alternative approach to assess the growth-climate response pattern in mountain forests and warranting the use of the space-for-time substitution in studies of climate change ecology.