Abstract: The distribution and assembly of plant species is a fundamental ecological question. Understanding how various drivers of community assembly vary along elevational gradients and differentially affect species occurrence versus abundance is critically important. Using an advanced tool, the joint species distribution model (JSDM), we aim to investigate shifts in the relative importance of climatic and non-climatic effects on forest community assembly along large elevational gradients, and to compare the elevational trends of these effects on species occurrence and abundance. We documented 243 forest plots, each with a size of 20 × 30 m, along elevational gradients (700–3650 m) of Qinling Mountains, the highest mountain in Central China. We performed JSDMs to quantify the relative importance of climatic and non-climatic effects on species occurrence and abundance along elevational gradients. Climatic and non-climatic effects exhibited distinct elevational trends and differed in their respective influences on species occurrence and abundance. The influence of climate on species abundance increased with elevation, whereas its effect on species occurrence showed a weak decline. At lower elevations, species occurrence was mainly determined by climate, while abundance was affected by both climatic and non-climatic drivers. At higher elevations, climate emerged as the dominant factor affecting both occurrence and abundance. Our study reveals different trends of climate and non-climate effects on species occurrence versus abundance. These findings underscore the importance of jointly considering both types of environmental drivers and both occurrence and abundance, which is critical for predicting community dynamics under climate change and guiding conservation strategies.

Key words: climatic and non-climatic effects, community assembly, elevational gradient, joint species distribution model (JSDM), species occurrence and abundance