The Classification And Evaluation Of Site Conditions In Lhasa Valley

The climate of Lhasa valley is dry, little rainfall, desertification seriously. In order to improve the local ecological, residential and grazing environment, we need for artificial vegetation restoration, construction sand-fixing, erosion of ecological safety net. In this paper, choosed the four representative experiments of Lhasa river valley, surveyed the experimental land topography, soil, water and vegetation, etc., by using principal component analysis, cluster analysis and AHP, we had the results as follows:1. 6 Site Classification System. According to "China Forest Site Classification", the Lhasa Valley's site is divided into: the Brahmaputra River established areas, the Brahmaputra River valley sub-district site, Lhasa River valley site type cell, and then divided into the following groups and specific site type site type, a total of 5 level classification system.2. The topography of Lhasa valley determines the four different site type group: flood land group of site type, platform group of site type, slope group of site type, alluvial fan group of site type.3. Principal component analysis of the site factors. The purpose of the analysis is to select one of the dominant factors. Flood land selected three main components, the cumulative contribution rate of variance accounted for 82.117%; platform, the slope, alluvial fans selected three main components, the cumulative contribution rate of variance accounted for 85.801%.4. By classify analyze with the shortest distance method in spss13.0, had flood land, platform, foothills slope stand, and alluvial fan's site type.5. The study of soilmass structural patterns.Lhasa semi-arid valley's soilmass structural patterns can be divided into five categories: homogeneous type, bottom type, size type,heart-shaped type and three-section type. Homogeneous type of Pebble Beach to the worst, the other thick soil profile, rich in vegetation, soil configuration is better. Size, three-section type and heart-shaped configuration of the soil is general,and it's soil has many differences, which of thin soil needs a large number of foreign soil.6. From the study of the clustering and soil configuration's results,we can divide the Lhasa valley into 16 site types.The 16 site types are the basis of the site classification in Lhasa valley.7. Site Quality Evaluation. AHP method is used to establish the site quality evaluation index system of Lhasa semi-arid valley.The results showed that: only a handful of Lhasa Valley site is excellent and poor ratings. Most's score is the good, accounting for 79.7% of the samples. Score very poor pebble beach can not to reforest.The result of evaluating being the superior can afforest directly, the other sites need soil improvements before planting.8. Afforestation measures. Different types of site type and site quality evaluation results need different method.Evaluation of antagonism can planting for the excellent, good ,and the opposition,the site of bad scores need for the foreign soil.