Biomass And Comparisons Of Its Effect On Soil Water Content Between Artificial And Natural Vegetation In Yanhe River Catchment

The loess plateau is the most serious soil erosion area in China with serious vegetation degeneration and weak ecological environment. Vegetation restoration and reconstruction is an important way to control soil erosion and to improve the ecological environment. Soil water content is the key factor limiting vegetation reconstruction, and because of deficiencies in species selection and arrangement of vegetation, numerous problems such as single species and structure exist in the work of vegetation. Excessive consumption of soil water content caused by oversize density of artificial vegetation and overtop community productivity results in the vegetation of degradation, soil drying, soil fertility declination etc. This study analyzes the relationship of vegetation and soil water content, evaluates the biomass carrying conditions of soil water content of artificial vegetation, and puts forward the upper limit range of artificial vegetation carrying, with the biomass carrying capacity of the soil water content of natural vegetation for reference. The main conclusions are as follows:1) Through space distribution figure got by the Kriging interpolation method, it is indicated that natural vegetation biomass in Yanhe River catchment on the whole present the spatial pattern of gradually increasing from northwest to southeast; although the change rule of artificial vegetation is not obvious, it can be seen that the artificial vegetation biomass in the north-central region present obvious overload phenomenon.2) Spatial variation of natural vegetation biomass and rainfall gradient closely related, and biomass gradually increasing as the rainfall increases from northwest to southeast (p<0.05, R~2 = 0.65); the above-ground biomass of artificial vegetation has no obvious growth (p>0.05) trend with the increases of rainfall gradient.3) The results of variance analysis showed that natural vegetation biomass in flat and lower slope were very significantly lower than artificial vegetation biomass (F=10.912, 11.477, p < 0.01), but natural vegetation biomass in upper slope and middle slope were significantly below (p < 0.05) than those of artificial vegetation biomass. Natural vegetation biomass in semi-shady was significantly higher than in shady, semi-sunny slop and sunny slope. However, artificial vegetation biomass had no significant among the slope.4) Correlation analysis between above-ground biomass and soil water content of natural vegetation is carried out in three areas of Yanhe River catchment, the northern region, central region and the southern region. The results show that biomass and soil water content of natural vegetation in the northern region of the catchment present a negative relationship (p>0.05), that is, soil water content decreases along with the growth of vegetation, and that there is no significant positive correlation between above-ground biomass and soil water content of natural vegetation in the central and southern region of the catchment (p>0.05), nevertheless, along with the supply of rainfall, vegetation grows vigorously, and the water retain ability of soil is also improved.5) Vertical distribution difference analysis of 0-500 cm average soil water content indicates that moisture change trend of natural and artificial vegetation in the northern area basically consistent with each other. While artificial vegetation boosts the vegetation biomass, the increasing biomass will cause excessive consumption of soil water content. Water consumption levels of natural vegetation in the central area is approximately 0-70 cm, and water consumption levels of artificial vegetation is relatively deeper than that of natural vegetation, and holds the whole soil profile, however, the main water absorbing layer is 0-110 cm. Robinia pseudoacacia, the main artificially vegetation in the area, need a lot of soil water content in order to maintain high biomass, and thus lead to serious deficit of soil water content. There is no obvious differences of soil water content between artificial and natural vegetation in the southern area which is different from the obvious distinction of condition of the central and northern areas. Better condition of rainfall can accommodate larger biomass, therefore, the biomass of artificial vegetation in this region may not seriously influence the ecological environment.6) With natural vegetation as reference, it is found that artificial vegetation overload condition in the central region of Yanhe River catchment are relatively serious, soil water content content present serious deficit, the northern region taking the second place, and the southern region showing less overloading position or even no overloading position. When Soil water content decline to the critical value at which Robinia pseudoacacia cannot survive, the upper limits of artificial vegetation overloading are 7.13 times in the north, 16.12 times in the centre and 45.41 times in the south.