Land Degradation Assessment In Liusha Basin Based On "3S" Techniques

According to the data of field investigation for both plant identification and soil chemical analysis of 61 samplings in 2005 in the Liusha Basin, Hanyuan County, Sichuan Province, land degradation of the Liusha Basin were assessed by multiple statistic methods. Status quo distribution of land degradation were made through assessment results and judgment of remote sensing images, the degraded area, vegetation and soil character of samplings were analyzed under different land degradation degrees, simultaneously; and then degradation factors were studied, finally the Land degradation prevention and cure measures were brought forward in the light of aforementioned analysis. The main results were as follows.The 32 initial indices from topography, vegetation and soil were selected by PCAcombined with specialty knowledge, of which 10 indices were finally chosen to be the land degradation assessment indices, including aspect, biomass, cover, H', depth, bulk density, aggregation degree, pH, SOM and SAK.K-means cluster associated with discriminant analysis was applied to classifying sampling plots into 4 sorts," CK, light degradation, moderate degradation and severe degradation. The total degraded area was 413.83km², the area under different landdegradation degrees were 68.15km², 76.87km²,117.85km² and 150.96km² in turn, and of which the percentage were 16.47, 18.58, 28.48 and 36.49 of total degraded area, respectively.Vegetation and soil character were analyzed under different land degradation degrees.Variance analysis indicated that as the severity of land degradation enhanced, depth, aggregation degree, SOM and STN content presented a significant or highly significant declined tendency; while soil bulk density and pH presented a significant or highly significant rising tendency, on the whole. Furthmore, vegetation quantitative characteristics, species diversity and species richness indices were all significantly or highly significantly declined whereas evenness indices was significantly or highly significantly increased. As far as species composition was concerned, 110 species were collected within investigated plots. 60 species belonged to 12 families (Gramineae, Compositae, Rosaceae, Leguminosae, Caprifoliaceae, Ranunculaceae, Anacardiaceae, Pinaceae, Moraceae, Coriariaceae, Acanthaceae and Salicaceae ) was 66.67 percentof total species and of which dry plants was 83.88 percent. This reflected study area's vegetation characteristic. Along with the severity of land degradation, both the species number and frequency of Gramineae, Compositae and Leguminosae were increased while Pinaceae, Salicaceae and Rosaceae were declined.The main influential factors of land degradation in Liusha Basin were altitude, the intensity of human disturbance, land use types and road. Variance analysis showed that biomass, H' and D₃ were generally highly significantly increased along with the rising of altitude, while cover and Jsw were of no significant difference among different altitude grads; depth, aggregation degree and SOM content presented a significant or highly significant increasing tendency; whereas bulk density presented a decreasing tendency. As the intensity of human disturbance enhanced, biomass, cover, H' and D₃ were significantly or highly significantly declined, while Jsw was significantly or highly significantly increased on the whole; depth, aggregation degree and SOM content were highly significantly decreased, however bulk density presented a significant or highly significant increasing tendency. Among different land use types, biomass, cover and D₃ of forest land were all highly significantly higher than that of the other three land use types, nevertheless Jsw of forest land was significantly or highly significantly lower than that of the other three, whereas H' was of no significant difference among different land use types; depth and SOM content under forest land were both highly significantly higher than that of the other three types, bulk density under forest land was significantly lower than that of the other three, whereas aggregation was not significantly different among different land use types. As the distance of the road increased, biomass, cover, H' and D₃ were presented asignificant or highly significant increasing tendency, while Jsw under middle-distance was highly significantly higher than that of remote distance, but there was no significant difference between close and middle-distance; Both depth and SOM content were showed a highly significant increasing tendency, while bulk density was highly significantly decreased, and however aggregation was not significantly different among different distance.On the basis of land degradation assessment and influential factors analysis, this paper put forward following land degradation prevention and cure measures, including actualizenatural forest conservation project, enhance vegetation cover, father mine and reinforce road protection project.