Altitude differences in relationship between radial growth process and cambial phenology of Qinghai spruce (Picea crassifolia) on the Tibetan Plateau

Abstract

Climate change profoundly affects tree radial growth dynamics and phenological changes, yet the relationships between radial growth and cambial phenology of dominant tree species at different altitudes on the Tibetan Plateau remain unclear under the background of climate change. In this study, we analyzed the characteristics and relationships between intra-annual growth rates and growth phenology of Qinghai spruce using tree-ring width data from 1973 to 2022 at different altitudes on the Tibetan Plateau based on a growth process model. The results showed that the inter-annual variations of radial growth at high altitude exhibited a gradual increasing trend, with intra-annual growth rates displaying a unimodal pattern. Additionally, there were no significant differences in growth rates dependence on temperature and soil moisture between wide and narrow rings. Inter-annual variations of radial growth at low altitude showed a gradual decreasing trend, with intra-annual growth rates exhibiting a bimodal pattern. Growth rates dependence on temperature did not differ significantly between wide and narrow rings, but the growth rates dependence on soil moisture was significantly different. Phenological characteristics are the key factors to determine inter-annual tree radial growth at high altitude, while both phenological characteristics and soil moisture are the main reasons to determine inter-annual and intra-annual tree radial growth at low altitude. The findings provide a theoretical basis for scientific management of forest ecosystems at different altitudes on the Tibetan Plateau and accurate prediction of forest growth dynamics under future climate change.