Response sensitivity processes of conifers radial growth to climate factors based on tree ring width variations

The tree radial growth process exhibits complex signals in response to climate change. These signals can significantly influence the tree growth process. Essential physiological factors play a critical role in determining growth-response differences. However, the mechanisms affecting the nonlinear response of conifer species growth to climate change have yet to be fully elucidated. In this study, we measured the characteristic signals of growth process-wide (narrow) rings from two conifer species, Qinghai spruce (Picea crassifolia Kom.) and Chinese pine (Pinus tabuliformis Carr.) in the subalpine zone at the southern edge of the Tengger Desert, and analyzed their phenology and seasonal water-heat utilization dynamic mechanisms using the process-based Vaganov-Shashkin model (VS-oscilloscope). Our investigation demonstrates that both species are sensitive to temperature, although P. crassifolia is more responsive to temperature-induced drought stress. Furthermore, the phenology and seasonal water-heat utilization dynamics are the main driving forces behind the climate response sensitivity and radial growth trends of conifer species. The study revealed earlier dormancy for both species in narrow rings, as well as earlier growth initiation for P. crassifolia. Additionally, temperature was identified as the key cause of growth decline trends in the middle growing season. The limited soil moisture caused by temperature-induced deficits in the end growing seasons was also responsible for the frequent narrow rings of P. tabuliformis. Therefore, we propose that management and conservation measures for subalpine ecosystems should be formulated based on the response sensitivity and physiological mechanism of conifer species.