Modeling the distribution pattern of Sapindus mukoross using the Biomod2 ensemble model

Sapindus mukorossi is an important woody oil plant and clean energy tree species in China. This study employed the Biomod2 ensemble model to simulate the potentially suitable distribution areas of S. mukorossi across different periods and to analyze the dominant environmental factors limiting its distribution. The aim was to provide a theoretical basis for the cultivation zoning of S. mukorossi.

Geographical distribution data of S. mukorossi for the current period were obtained through database queries, literature retrieval, and field surveys. R language and ArcGIS software were used to screen the geographical distribution points. Variance inflation factor (VIF) and Pearson correlation coefficient tests were applied to screen climate, soil, and topographic factors. Model accuracy was evaluated using the true skill statistic (TSS), Kappa coefficient, and the area under the receiver operating characteristic curve (AUC). The dominant environmental factors constraining the geographical distribution of S. mukorossi were identified using the jackknife test combined with environmental factor contribution rates. Species distribution models within the Biomod2 package were integrated using a weighted mean approach to build an ensemble model. This model was used to simulate the potential distribution areas of S. mukorossi during the last glacial maximum (LGM), mid-holocene, current period (1970-2000s), and Future period (2041-2060s). The natural breaks method was used to classify the suitability levels of the distribution areas.

The ensemble model demonstrated higher accuracy and better performance than all individual models. The dominant environmental factors constraining the geographical distribution of S. mukorossi were: mean precipitation of the warmest quarter (350-1 650 mm), isothermality (5%-53%), maximum temperature of the warmest month (18-37 ℃), and Mean Temperature of Wettest Quarter (15-32 ℃). From the LGM to the Mid-Holocene, S. mukorossi was mainly distributed on the Tibetan Plateau. Since the Mid-Holocene, the area of its potentially suitable distribution has continuously expanded. Under future climate scenarios, the potentially suitable distribution area for S. mukorossi is projected to continue expanding.

The Tibetan Plateau may have served as a glacial refuge for S. mukorossi. The dominant environmental factors influencing its geographical distribution are temperature, precipitation, and isothermality during its growth and development period. The species is most suitable for distribution in subtropical monsoon humid climate zones. Under different future climate scenarios, the potentially suitable distribution area of S. mukorossi shows a trend of fragmented expansion. The findings of this study provide guidance for promoting the cultivation of S. mukorossi plantation resources and the development of its related industries.