Altitudinal Variation in Effect of Climate and Neighborhood Competition on Radial Growth of Picea Schrenkiana in the Middle Tianshan Mountains, China

Tree growth plays the most important role in carbon sequestration in forest ecosystems and is gaining growing significance given the increasing impact of climate change. Both climate and competition are critical biotic and abiotic factors affecting tree growth. However, the response mechanism of tree growth at different altitudes to climate and neighbor competition has not been clarified, especially in arid regions such as Central Asia. In this research, we investigated the effects of climatic factors and competition on the radial growth of Picea shrenkiana at different altitudes, and examined their spatial variability based on dendroclimatology, competition analysis, principal component analysis (PCA), multiple linear regression analysis, and correlation analysis in 12 plots at different altitudes (1500 m to 2650 m) in the Middle Tianshan Mountains. The results showed that radial growth of Picea shrenkiana varies significantly in response to climatic factors and competition across altitudes. In the low altitudes, growth is mainly limited by water-related factors including drought index and spring precipitation, while high temperatures inhibit growth. At middle altitudes, growth is driven by both climate and competition, with climate factors, especially spring moisture, playing a dominant role. At high altitudes, the growth is affected by both temperature-related factors and neighbor competition, and the sensitivity of growth to climate decreases.The results of this research suggest that the radial growth response of Picea shrenkiana to climate and competition exhibits significant spatial variation, transitioning from water limitation at low altitudes to co-driving influences of climate and competition at higher altitudes. Future climate warming may exacerbate drought stress at lower elevations, while mid and high elevations may benefit from extended growing seasons due to warmer temperatures. In the context of climate change, these findings provide a basis for ecological management and sustainable conservation of arid mountain forests.