MaxEnt Modelling for Predicting the Potential Distribution of an Endangered and Nationally Protected Tree Species (Machilus nanmu) Under Climate Change and Human Activities

Global climate change and intensifying anthropogenic pressures pose unprecedented challenges to global biodiversity, with endangered species often experiencing particularly severe reductions in suitable habitats. In this study, we used the MaxEnt model to predict and evaluate the potential suitable habitats of Machilus nanmu in China under current and future climate scenarios. After parameter optimization (RM = 0.5, FC = LQH), the model showed excellent predictive performance, with a mean AUC of 0.946 and a CBI value of 0.988. The analysis of key environmental variables indicated that Mean UV-B of the High-est Month (Uvb3, 24.5% contribution), Temperature Seasonality (bio4, 19.6%), and Population Distribution (human_pd, 19.5%) were the dominant factors shaping habitat suitability, while Temperature Seasonality had the highest permutation importance (34.1%). Under current conditions, the highly suitable habitat area was estimated to be approximately 21,109.94 km2, accounting for 0.22% of the total study area, and was mainly concentrated in the Sichuan Basin and the Yunnan-Guizhou Plateau. Under future climate scenarios, the highly suitable area of M. nanmu under the low-emission scenario (SSP1–2.6) showed an overall fluctuating trend, with an initial decline followed by a later expansion, resulting in an approximately 6.3% increase by the 2090s relative to the current period. In contrast, under the medium-emission scenario (SSP2–4.5), the highly suitable area also exhibited fluctuations but ultimately increased by approximately 3.9% by the 2090s. Centroid shift analysis further revealed an oscillatory east–west migration pattern of distribution centroids under SSP1–2.6, with a brief southwestward shift between the 2050s and 2070s, whereas under SSP2–4.5 the centroid trajectory was more complex: it first shifted westward and northward, then moved significantly southwestward, and finally turned eastward. These findings highlight the significant impacts of climate change on the suitable habitats of M. nanmu and provide a scientific basis for its conservation and sustainable management.