[Community characteristics of Hippophae rhamnoides forest and water and nutrient condition of the woodland in Loess hilly region].

To improve the productivity of Hippophae rhamnoides forest and to manage the forest reasonably, the community characteristics of Hippophae rhamnoides and the water and nutrient condition of the woodland were analyzed. The results showed that Hippophae rhamnoides grew fast and its adaptability was strong. 4-5 years old Hippophae rhamnoides could form shrubs-grass community. The biomass 1-8 years old Hippophae rhamnoides increased rapidly, but that of 8-11 years old increased more slowly. Hippophae rhamnoides older than 11 years could keep reasonable community structure and higher primary productivity by natural thinning. The utilization of soil moisture by Hippophae rhamnoides could be classified into four layers as faint utilization layer of root system (0-20 cm), utilization of root system (20-300 cm), adjustment layer supplied by soil moisture (300-400 cm), and faint adjustment layer (400-500 cm). Due to the soil improvement by Hippophae rhamnoides and the water retaining by litter, the soil moisture of 1-1.5 m layer could be easy to restore. Hippophae rhamnoides could keep the balance of nutrition in the woodland through the fixation of nitrogen by root nodule and the decomposition of litter. In the 6-9 years old Hippophae rhamnoides plantation, the total nitrogen content of soil might be improved from 0.05-0.1% to 0.2%.