Vegetation differentiation characteristics and control mechanisms in the Altay region based on topographic gradients

Among numerous vegetation studies, there are few studies on the elevation gradient distribution control mechanism and horizontal law of small-scale vegetation. In the same climate zone, topography is one of the most important factors affecting vegetation pattern. Here, we used the geo-informatic Tupu theory to construct topographic gradient-vegetation distribution information Tupu (TG-VDI Tupu) to display the topographical differentiation characteristics of vegetation. Moreover, an improved evaluation of topographical differentiation characteristics of vegetation was proposed based on topographic gradients, and the topographic composite index (TCI) was constructed to analyse the topographic variation in vegetation distribution. Meanwhile, the dominant factors and limiting factors affecting vegetation distribution under different topographic gradients were determined through statistical analysis. Combined with field surveys, Gaofen-1 (GF-1) satellite images were used to extract vegetation types, and the solar radiation value (SRV), topographic wetness index (TWI) and topographic variables were extracted from DEM data. The results indicate that TG-VDI Tupu can visually display topographic differentiation characteristics of vegetation on an elevation gradient. Elevation controls the horizontal distribution of vegetation on a small scale by changing ecological factors. At the same elevation, slope affects vegetation distribution by changing the SRV and TWI, while aspect changes the TWI. Coniferous forest is separated along a slope gradient and is more abundant on steep slopes. The percentage of broadleaf forest is negatively correlated with SRV and positively correlated with TWI, and the proportion is higher on the leeward slope facing north. The distribution of shrubs is more abundant on more xeric aspects and on steeper and more xeric slope configurations. In alpine areas above 2800 m, the abundance of vegetation types declines. This decline may be related to the weak solar radiation and widespread glacial landforms, exposed rocks and strong weathering. The methodology in our study can be applied to other regions and is expected to provide useful information for ecological conservation policy making.