| The Loess Plateau is one of the most serious soil erosion areas in the world with unique environmental background and processes of soil erosion, which is located in the semi-arid and semi-humid climate zone. Since the implementation of returning farmland to forestland (grassland) in 1999, the vegetation construction on the Loess Plateau has been greatly improved. In the study areas in Jixian County, Shanxi Province, Wuqi County, Shaanxi Province and Suide County, based on Quickbird images of same time phase in 6-9 years periods and 5m × 5 m DEMs, the present situation of vegetation restoration of 6-9a in 3 research areas since returning farmland to forest (grassland), the differences of vegetation restoration in different site types and the area of the land use types were compared and analyzed with RS and GIS techniques and statistical methods. The main conclusions were as follows:(1) Vegetation coverage increased on all 8 types of site conditions in Wuqi study area. The vegetation coverage on slightly steep sunny slope (15°-25°) and steep sunny slope (25°-35°) was about 6% lower than corresponding shady slopes, while little differences were found between sunny and shady gentle slope (<15°) or sunny and shady extremely steep slope (> 35°). It was difficult to restore vegetation on steep sunny slope and extremely steep slope in Wuqi study area where the vegetation coverage were still less than 50%, significantly lower than other types of sites after more than 10 years of returning farmland to forestland (grassland).(2) During 6-9 years periods, the area with coverage below 45% were decreased to different extent in the three study area in Wuqi, Jixian and Suide. Vegetation in Jixian was recovered to the highest coverage among the three study areas followed by Suide and then Wuqi, corresponding to their water and heat conditions.(3) After more than 10 years of restoration in Wuqi study area, low coverage vegetation (<30%) was mainly distributed on steep slope and extremely steep slope. Vegetation on various types of sites in Jixian study area was recovered in the similar degree owing to its better water and heat conditions while larger proportion of low coverage vegetation was on gentle slope in Jixian than in Wuqi. The study area of Suide, low coverage vegetation in each grade slope ratio did not change significantly.(4) Vegetation types change from the point of view, in Jixian study area, main land use types of woodland and the area ratio reached 50.32%; In Wuqi Study area, the main land use types is the grassland, there are a certain proportion of shrub forest, the area ratio respectively is 61.43% and 27.68%; In Suide study area,the main land use types is grassland, the area ratio reaches 88.43%. (5) From the difference of vegetation restoration under different site conditions, in the Wuqi study area, steep sunny slope and extremely steep slope is the type with poor habitat conditions,shrub forests has little increase, while the low coverage grassland reduced significantly; In the Jixian study area, in good habitat of gentle slope land area is small, low cover grassland area has little reduction, but the steep slope and extremely steep slope got a full In the study area of Suide, in better habitat conditions of gentle slope has good vegetation recovery, in the steep sunny slope and extremely steep slope, the forest area has slight changes, the increase of grassland with high and medium coverage is not significant, low coverage grassland has not been fully restored.(6) The patterns of land use are similar in Wu Qi, Jixian, Suide study areas, with high and medium coverage grassland and forest land increasedsignificantly, and cultivated land and residential land decreased significantly.This paper could provide a reference for comprehensively appraising the project of returning farmland to forestland (grassland) on the loess plateau. |
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