Disparity in the relative roles of biotic and abiotic drivers on tree mortality between warm-temperate and temperate forests in China

Abstract

Tree mortality is a key component of carbon cycling and forest dynamics. However, the relative contributions of different mechanisms to tree mortality remain poorly understood, particularly in forests with different climates. To clarify the relative contributions of certain factors on tree mortality at various organizational levels, we censused the mortality of tree species in 4-ha Guandi Mountain (GDS) plot with a warm-temperate climate and in 25-ha Changbai Mountain (CBS) plot with a temperate climate in North and Northeast China, respectively. The generalized linear mixed model (GLMM) was implemented to examine the relative importance of biotic and abiotic factors on tree mortality. Of the variables tested, tree size was typically the most important factor in decreasing tree mortality at the community and guild levels in both GDS and CBS, and its negative effect was stronger in GDS. Neighbors’ variables had significantly positive effects on tree mortality in two plots. Differently, conspecific neighbors’ interactions had stronger facilitative effects on increasing tree mortality of community level, shade-tolerant, evergreen, and small trees (DBH < 10 cm) in GDS, while the heterospecific neighbors’ interactions played greater roles in facilitating tree mortality of community level, shade-tolerant, deciduous, small trees in CBS. Among the abiotic factors tested, convexity and soil nutrients had significant positive effects on increasing tree mortality of shade-tolerant, evergreen, and small trees in GDS. While the abiotic factors didn’t contribute significantly to tree mortality at the community and all guild levels in CBS. Accordingly, our study demonstrates that the relative importance of variables driving tree mortality varied dramatically among guilds and between warm-temperate and temperate forests. These results provide critical information for future studies assessing forest dynamics and offer insights contributing to forest management in different forests.