Abstract:

In the study, we have statistically analyzed the spatial and temporal changes in vegetation cover in the headwaters of the Changjiang River from 1982 to 2003, as well as the causing factors, including both natural and artificial ones, by using remote sensing image processing and geographic information technology based on GIMMS (Global Inventory Modeling and Mapping Studies)NDVI (Normalization Difference Vegetation Index) data and thematic vegetation information. Although the major trend of vegetation cover is rising through the recent 22 years, hygrophilous plants are gradually replaced by droughtenduring plants because of drought variations, which means the habitat of the vegetation is becoming dry. It is found out that the vegetation degradation is mainly influenced by the altitude, the aspect, the human activities and the groundwater level. The region in the altitude from 4400 to 4600 meters, which is mainly covered by alpine meadow and alpine swamp meadow, is strongly degraded by the stock raising with its influence radius of about 24 kilometers. The influence distance perpendicular to roads is also 24 kilometers, since road construction accelerates humaninduced destruction to vegetation. Vegetation in shade aspect is rising due to the increase in precipitation, while vegetation in sunny aspect tends to be stable or degraded because of the enhancement in sunlight. Furthermore, the vegetation coverage is influenced by the groundwater level. In near riverbed fields, where the depth of groundwater is shallow, plants can easily grow; while in far riverbed fields, vegetation is prone to degrade due to drainage. The radius of river influence is 24 kilometers.

Key words:

headwater region of the Changjiang River; vegetation index; remote sensing; Geographic Information System (GIS)