Effects of soil and climatic factors on the potential distribution of Castanopsis eyrei in China

The geographical distributions of plant species are being actively reshaped by climate change. <i>Castanopsis eyrei</i>, a cornerstone species of subtropical evergreen broad-leaved forests in China, plays a critical role in community assembly and carbon sequestration. Understanding the key factors driving shifts in its potential distribution is vital to maintain biodiversity and formulate effective conservation strategies. Here, by comparing the soil-topographic-bioclimatic model with the bioclimatic-only model, we found that soil (base saturation) and climate (annual mean temperature, precipitation of the coldest quarter) jointly constrain the potential distribution of <i>C. eyrei</i>. The bioclimate-only model predicted larger suitable areas, highlighting that non-climatic variables can substantially alter the potential distribution forecasts. For the period 2041-2060, both models projected relatively stable distributions under low-emission (SSP1-2.6) and high-emission (SSP5-8.5) scenarios, with the latter showing greater northward expansion likely associated with increased temperature and precipitation. The soil-topographic-bioclimatic models showed lower inter-scenario variability, suggesting that soil and topographic factors may buffer against the effects of climatic change within our modeling framework. Our study demonstrates the necessity of integrating non-climatic variables into species distribution models, and provides projections to guide future monitoring and conservation efforts for <i>C. eyrei</i>.