Abstract: Analyzing the carbon storage distribution pattern and its influencing factors of typical forest ecosystems in loess hilly region can provide support for the evaluation of forest carbon pool on the Loess Plateau. In this study, Pinus tabuliformis forest, Robinia pseudoacacia forest, Platycladus orientalis forest, Pinus tabuliformis+Robinia pseudoacacia mixed forest, and Platycladus orientalis+Robinia pseudoacacia mixed forest were selected as research objects in loess hilly region. The distribution characteristics and influencing factors of carbon storage in vegetation layer (tree, shrub, grass, and litter) and 0-100 cm soil layer of typical forest ecosystems in loess hilly region were analyzed by plot investigation method combined with principal component analysis and random forest model. The results showed that: (1) Ecosystem carbon storage was in order of Pinus tabuliformis+Robinia pseudoacacia mixed forest > Platycladus orientalis+Robinia pseudoacacia mixed forest > Pinus tabuliformis forest > Robinia pseudoacacia forest > Platycladus orientalis forest. Vegetation carbon storage of the Pinus tabuliformis+Robinia pseudoacacia mixed forest was the largest, while the Robinia pseudoacacia forest the smallest. Soil carbon storage was the highest in the Platycladus orientalis+Robinia pseudoacacia mixed forest and the lowest in the Platycladus orientalis forest. (2) There was a positive relationship of carbon storage between vegetation and soil, accounting for 15.72%-34.86% and 65.14%-84.28% of total ecosystem carbon storage, respectively. Soil carbon storage was the main body of ecosystem carbon storage. The ratio of underground and aboveground carbon storage varied from 1.87 to 5.36, and the vegetation layer still had strong carbon sequestration potential. (3) Soil total nitrogen, total phosphorus, available phosphorus, soil available potassium, soil clay, and plant diversity explained 84.14% and 95.88% of variation of carbon storage in vegetation layer and soil layer, respectively. Among them, biomass (26.25%) had the greatest contribution to the variation of carbon storage in vegetation layer. Total nitrogen (19.01%), total phosphorus (18.41%) and available potassium (15.28%) were the main factors affecting the vertical distribution of soil carbon storage. The carbon storage of forest ecosystems in loess hilly region was affected by community characteristics and soil physical and chemical properties. Under the similar stand age, carbon storage of mixed forest was higher than that of pure forest. Coniferous and broad-leaved mixed forest can be preferred when planting artificial forest on the Loess Plateau.

Key words: loess hilly region, forest ecosystem, carbon storage, distribution pattern, influencing factor