Relationships between vegetation and climate on the Loess Plateau in China

The Loess Plateau is one of the most environmentally sensitive regions in China. This study addresses the relationships between vegetation and climate of this area quantitatively at a large-scale, in order to determine the factors that control vegetation distribution. The Loess Plateau, located at 101 degrees 01 '-115 degrees 10 ' E and 34 degrees 02 '-40 degrees 40 ' N, covers an area of 52 million hectares. Vegetation data were collected from the vegetation map (1 : 500,000) and the Landsat Thematic Mapper scenes of the Loess Plateau. The Loess Plateau was divided into small districts of 30 ' latitude by 30 ' longitude on the vegetation map. In each district, areas with different vegetation were measured and used as vegetation data. The climatic data were average values of county meteorological records in each district in the past 25 years. GIS, TWINSPAN and canonical correspondence analysis (CCA) were employed for analysis. 257 small districts were clustered into 7 groups using TWINSPAN, representing 7 vegetation regions or subregions. The first three CCA axes had significant correlations with climate. The first CCA axis represented the variation of vegetation and climate along the latitude gradient, while the second CCA axis the variation along the longitude gradient. The distribution pattern of 171 vegetation formations on the CCA plot is identical to that of vegetation regions (districts). The spatial distribution of vegetation is closely related to climate variables on the Loess Plateau. Water variables and temperature are important in both latitude and longitude gradients, while the sunshine hours, accumulated temperature and wind speed are more important than water variables and temperature in longitude gradients.