Inventory survey of conversion farmlands to forest by Landsat TM and field survey in upstream of Yangtze rivers in China

摘要

In 1998, the Chinese government established the Natural Forest Conservation Program (NFCP). The NFCP was applied to 18 provinces and autonomous regions, which emphasize the upstream regions of major rivers' drainage area, specifically the Yangtze and Yellow Rivers where had have suffered massive ecological degradation and deforestation in the past 50 years. One of the most important tasks of NFCP was to mandatory conversion of marginal farmlands to forest where topographical slope gradient was more than 25 degree. It has been four to five years since mandatory conversion of farmlands to forest was implemented. But how about the effect of the implementation? Aiming at Jiulong county, Sichuan province, a portion of Yangtze Rivers upstream, we surveyed the effect of farmlands reforestation in support of RS (remote sensing) ,GIS (geographical information system) and GPS (Global Positional System) technology, and attempted to apply RS technology to the special ravine terrain region where the proportion of farmland is extraordinarily small (0.6%). According to the survey results from different periods of remote sensing datum (1999 and 2003) and field research, it could be concluded as follows: (1) In order to get more public subsidy of reforestation or regrassation, the local government registrated farmland area was much more than actual reforested area in practice. In our research region, only average 20.1% (the bias of estimation is -15.4%o) farmlands area had been reforested actually, however, the local government registrated that was 84.6%o. (2) and the most serious problems in the reforestation are: selection of canopy forest species only (most of them are climax species) in reforesting, planting of few pure tree species in the whole region and neglect of the adaptation of variation ecotype to local environmental conditions. The paper also analyzed that how to make use of some theories of ecology and theirs applications to reforestation supported by the GIS technology in local region.