Bashania fargesii is one of the middle-large amphipodial bamboos,which distributes mainly in the deciduous broad-leaved forests or coniferous and broad-leaved mixed forests in the elevation of 1100-1900 m in Qinling Mountains. The bamboo (Bashania fargesii) is the principal food source for Qinling giant pandas in winter and spring. The giant pandas' survival and activity are associated with growth status, quantity and spatial pattern of Bashania fargesii. The bamboo biomass is crucial in exploring Qinling giant pandas' habitats selection, but also in providing guidelines for the conservation actions of Qinling giant pandas. However, there is lack of empirical research on the spatial distribution characteristics of Bashania fargesii biomass. This study was aimed to investigate the site effects on Bashania fargesii biomass distribution. The key factors and the suitable site condition for the bamboo growth were assessed. The bamboo biomass, height, basal diameter, population, and density with different site conditions (including elevation, slope, slope position, slope aspect, and canopy closure) were measured in 54 sample plots of giant pandas habitat in Foping, Huangbaiyuan and Pingheliang natural reserves. These natural reserves are located on south-facing slope in the middle of the Qinling Mountains in Shaanxi Province. In this research, the effects of different site conditions on the bamboo biomass were analyzed by using the methods of t test and multiple regression with SPSS software. Our results show that the distribution of the bamboo varied regularly by site factors as follows: (1) The bamboo biomass varied significantly in different investigated areas. In this study, the rich biomass density and favorable growth status were found in Foping and Huangbaiyuan natural reserves, while the poor biomass density and less favorable growth status in Pingheliang natural reserves. This was probably caused by the different hydrothermal conditions and characteristics of the community structure of the different investigated areas. (2) The bamboo biomass changed with elevation. The good bamboo communities were located between the elevation of 1500 m and 1700 m, while the bamboo communities were not observed below the elevation of 1300 m and above 1700 m. (3) The bamboo biomass decreased with the increase of slope, and the steep slope was hard for its growth compared with other slopes. (4) The upper slope was difficult for the bamboo growth. The biomass difference was insignificant between the mid and lower slope. (5) The effect of slope aspect on the bamboo biomass was insignificant. Both of the slope aspects were suitable for the bamboo growth. (6) There was a remarkable correlation between the bamboo biomass and the canopy closure. When canopy closure of deciduous broad-leaved forests or coniferous and broad-leaved mixed forests was over 0.6, the bamboo grew feeble.
In conclusion, the dominant site factors influencing Bashania fargesii biomass were slop position and canopy closure. The bamboo forests tend to grow relatively tall with thick stems and rich biomass on mid or lower and gentle slopes in deciduous broad-leaved forests or coniferous and broad-leaved mixed forests with medium canopy closure between the elevation of 1500 m and 1700 m. These areas seem to be the most suitable habitats for the giant pandas in winter and spring.