Effect of Cultivation of Different Tree Species on the Tree Increment and Soil Physical and Chemical Properties in the Same Site Condition

tree species (including Mytilaria laosensis, Gmelina arhaea,Michelia macclurei,Castanopsis hystrix, Tectona grandis and Pinus elliottii)have been planted in the same site in Xiashinazhao Mountain, Guangxi Province.Through a successive observation for 5 years, the results were as follows: 1.Except T.grandis, the other 5 species can grow well there.But the increment volume of the trees are different when they are growing on different parts of the slope, for example,the growing volume of G.arborea(7-year-old) at the lower part of the slope is 192.44 m3/hm2, while those at the middle and the upper part are 121.33、51.10 m3/hm2 respectively.The increment of broadleaf trees decreases with the raising of the location of the slope.The order for the reduced volume from the biggest to the smallest is C.hystrix,M.macclurei,G.arborea and M.laosensis.As for P.elloittii,the effect is not obvious.2.The effect of cultivation of different tree species on the soil properties varied.The volume weights of soil at the places where G.arborea,M.laosensis or P.elloittii was planted are heavier than those where C.hystrix or M.macclurei was planted, while the porosity and water holding capacity of soil are on the contrary to the above result.The organic nutrient of soil at the places where M.macclurei or G.arborea was planted is 10%～67%higher than those of the others.The content of soil available phosphorous at the place where G.arborea was planted is the lowest while the content of soil available potassium where M.laosensis was planted is the lowest.3.The soil volume weight and content of mineral elements of the barren hills are bigger than those of the afforested land.The content of organic nutrient is being increased with the increase of loseness of canopy.