Decoupled climate relationships of tree radial growth and canopy dynamics along environmental gradients in Qinling Mountains, central China

Radial growth and canopy dynamics of trees both play a significant role in the terrestrial carbon cycle. However, the climate-driven responses of these two key biomass compartments and their modulating factors across different growing seasons remain insufficiently understood. In this study, we integrated tree-ring chronologies with the normalized difference vegetation index (NDVI) from remote sensing to investigate the climate response of tree growth across 20 sites spanning different environmental gradients in the Qinling Mountains of central China. We calculated correlations of Tree-ring width and NDVI with climate factors and evaluated how these responses varied with aridity index, topographic wetness index, elevation and slope. The results revealed that decoupling of xylem and foliage climate responses was most significant in the early growing season, primarily driven by moisture availability, with both tree-ring width and NDVI showing stronger correlations with vapor pressure deficit (VPD) and temperature under improved moisture conditions. Notably, we observed a significant positive correlation between TRW and NDVI of the middle growing season. These findings demonstrate that climate response differences between radial growth and canopy dynamics may arise from their heterogeneous adaptive strategies along environmental gradients, highlighting the important scientific significance of joint assessment of both xylem and foliage growth for understanding forest growth dynamics under global change.