Effects Of Eucalyptus Afforestation On Soil Hydrological Fuction And Nutrient Loss

Vegetation change and afforestation activities are the major factors which affect the water storage capacity and the nutrient balance of forest land. The current Eucalyptus plantations in Guangxi are mainly changed from long-rotation forestry which was planted for more than15years. Because of the frequency afforestation and management measures, there are stronger impacts on soil and vegetation of eucalytus. And soil, as the important interface of rainfall redistribution in forestry, has influenced the surface runoff greatly. There would be significant difference on soil hydrology function after the forest land was changed into eucalyptus, which may directly affect the surface runoff, leading to the change of soil erosion and degradation. The influence of these changes would be expanded under the extreme weather conditions such as continual rainstorm.To better understand the effects of vegetation change on water storage capacity and nutrient loss in forestry, a simulated rainfall experiment and a laboratory analysis method had been used to evaluate the impacts on soil hydrological-physical properties, water storage capacity, surface runoff, soil erosion and the nutrient loss while the long-rotation forestry, such as Pinus massoniana, Cuninghamia lanceolatad and Myilaria laosensis, was replaced by short-rotation forest such as Eucalyptus urophylla×E.grandis. The main results are as follows:(1) The influence of soil and water storage is to enhance the reservoir capacity and the remaining water storage space of20-40cm layer when the plantation had been changed from long rotation forest into eucalyptus.(2) Afforestation with eucalyptus possibly decreases and delays the slope runoff within a certain rainfall intensity. There will be a difference in runoff regulation capability among different forests when the extreme rainfall (rainfall intensity is more than1.0mm.min-1) happens. The main factors affecting the slope runoff are rainfall intensity, soil infiltration rate and vegetation types. There is a quadratic parabola relationship between rainfall and runoff.(3) The change of soil erosion is less obvious when the rainfall intensity is lower than1.0mm.min-1. However, there will be a difference between the lands before and after afforestation under the extreme rainfall circumstance (rainfall intensity is more than1.0mm.min-1). The main factors affecting the erosion rate are rainfall intensity, runoff volume and litter content. Correlation coefficient is0.355,0.578and0.578, respectively.(4) Short-term rainfall has significant influence on nutrient loss in the forest land, the sequence is N>P>K. Afforestation with eucalyptus possibly decreases the content of N, P, K. There are positive correlations among the nutrient loss and runoff, rainfall intensity, soil erosion and vegetation types. The correlation coefficient is0.807,0.532,0.530and0.354, respectively.