GIS-assisted modelling of the spatial distribution of Qinghai spruce (Picea crassifolia) in the Qilian Mountains, northwestern China

The aim of this study was to predict Qinghai spruce (Picea crassifolia) distribution at the regional scale, i.e., where the extent of the prediction was within the biogeographic range of Qinghai spruce in the study area. First, we selected the main resource variables such as mean July temperature, soil moisture and solar radiation. These variables were spatialized as functions of elevation and geographical coordinates or as functions of aspect and slope via a GIS. Second, the niche spaces of Qinghai spruce were determined by incorporating the spatially-distributed resource variables with the current distribution of the species, which came from remote sensing data (Landsat TM image). The niche spaces defined then were extrapolated over the study area. Third the distribution pattern was calibrated by field investigations. The results show the niche spaces of Qinghai spruce: the scope of mean July temperature ranging from 8.5 /spl deg/C to 13.5/spl deg/C, average annual precipitation from 370 mm to 660 mm, the soil moisture index from 2.3 m/sup 3//m yr to 4.5 m/sup 3//m yr and the shortwave radiation for an average July day from 3.8 mm m/sup -2/ day/sup -1/ to 7.8 mm m/sup -2/ day/sup -1/. According to the niche, the elevation range belonging to Qinghai spruce in Qilian Mountains was extracted from DEM, which was about from 2600 m to 3400 m. The result was consistent with other investigations. We found that the density of the species has higher value from 2650 m to 3100 m based on the field investigation, and from the height 3100 m the density decreased with elevation increase. The basal area of Qinghai spruce had the same trend as the density. That is, the suitable niche of the species ranged from 2650 m to 3100 m.