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

There has been an increasing use of predictive spatial distribution of main communities or dominant species at the landscape scale for ecological restoration planning, biodiversity conservation planning and regional management decisions in the Qilian Mountains, northwest China. Understanding the spatial distribution of dominant species at the regional scale is also essential for assessing the impacts of environmental change or human effects on vegetation distribution. Based on the spatial distribution of resource variables that correlate with or control plant distribution, this study focused on the prediction of 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 upper reach of Heihe River. The development of the predictive model in the study required the integration of geographical information system (GIS) with remote sensing (RS), spatial analytic and statistical tools. First, we selected the main resource variables such as mean July temperature, water and solar radiation. These variables were spatialized as functions of elevation and horizontal 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 validated by field investigations. The study showed that the scope of mean July temperature ranged from 8.5 °C to 13.5 °C, average annual precipitation from 370 mm to 660 mm, the soil moisture index from 2.3 m3 m−1 year−1 to 4.5 m3 m−1 year−1and the shortwave radiation for an average July day from 3.8 mm m−2 day−1 to 7.8 mm m−2 day−1. The elevation range belonging to Qinghai spruce in Qilian Mountains was also determined according to the mean July temperature space occupied by the forest. The elevation occupied by Qinghai spruce was about from 2600 m to 3400 m. We found that the density of the species has higher value from 2650 m to 3100 m based on the field investigation, and from 3100 m the density decreased with elevation increase. The basal area of Qinghai spruce had the same change as the density. That is, the suitable niche of the species ranged from 2650 m to 3100 m.