Growth Suitability Evaluation of Larix principis-rupprechtii Mayr Based on Potential NPP under Different Climate Scenarios

Larch (Larix principis-rupprechtii Mayr) is a major coniferous tree species in northern China, and climate change has serious impacts on larch growth. However, the impact of future climate change on net primary productivity (NPP) and the growth suitability of larch is unclear. Based on forest inventory data, spatially continuous environmental factor data (climate, topography, soil), and NPP from the Carnegie-Ames-Stanford approach (CASA) model in the study area, the random forest (RF) model was used to simulate the potential NPP and growth suitability of larch under different shared socioeconomic pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5) for current and future (2041–2060, 2080–2100). The correlation between potential NPP and determinants under different climate scenarios was analyzed at the pixel scale. The results showed that: (1) RF showed excellent performance in predicting the potential NPP of the region (R2 = 0.80, MAE = 15.61 gC·m−2·a−1, RMSE = 29.68 gC·m−2·a−1). (2) Under current climatic conditions, the mean potential NPP of larch was 324.9 gC·m−2·a−1. Low growth suitability of larch occurred in most parts of the study area, and high growth suitability only existed in the Bashang area and the high-elevation mountains. (3) The total area of high and medium growth suitable areas were projected to be 76.0%, 66.7%, 78.2%, and 80.8% by the end of this century under the SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 climate scenarios, respectively. (4) Under the SSP1-2.6 and SSP2-4.5 climate scenarios, the temperature had a significant contribution to the accumulation of the larch’s NPP, whereas precipitation had less effect on the larch’s growth. The results provided a theoretical basis for the adaptive management of larch forests under global climate change.