Influence of stand and environmental factors on forest productivity of Platycladus orientalis plantations in Beijing's mountainous areas

The purpose of forest management is to establish a forest ecosystem with multifunction in Beijing's mountainous areas, and the priority is to increase forest productivity aiming to achieve carbon neutrality. In this study, we investigated 62 sample plots of Platycladus orientalis plantations and compared the relative contributions of stand and environmental factors to forest productivity by using variance partitioning analysis, the direct and indirect effects of these factors were explored by using structural equation model. And the geographical distribution of areas with higher forest productivity of Platycladus orientalis plantations was simulated and the contributions of these factors to the greater productivity was analyzed by using maximum entropy model (MaxEnt). The results indicated that topography was the dominant factors affecting the forest productivity of Platycladus orientalis plantations, followed by stand and soil nutrient factors. The results of structural equation model indicated that both topography and stand factors not only directly affect forest productivity, but also indirectly affect it by influencing soil nutrients. Soil nutrients had only direct impact on forest productivity. Forest productivity of Platycladus orientalis plantations was higher in areas with low altitude (168-252 m), gentle slopes (5-13 degrees), sunny slopes or semi-sunny slopes, soil total nitrogen content (>1.5 g/kg), and soil organic matter content (>38 g/kg). By changing the slopes to 5-13 degrees, increasing soil total nitrogen content to 1.5 g/kg and soil organic matter content to 38 g/kg, the average existence probability of higher forest productivity areas increased from 0.32 to 0.46, and amount of areas with higher productivity will be increased by approximately 43.8 %.