Characteristics of Rainfall Redistribution of Eucommia Ulmoides Planting in the Mid-Subtropical Zone

Hydrological process of canopy is an important consideration from forest ecological and hydrological points of view,which affects the total depth and spatial distribution of water input,lags the onset time of sub-canopy rainfall and influences the soil and water conservation in forest ecosystems.As a tree species commonly used for reforestation in southern China,Eucommia ulmoides serves an important example of water resource management and sustainability of long-term productivity.Therefore,the partitioning of gross rainfall into throughfall,stemflow and interception in the E.ulmoides forest was studied from July 2004 to September 2005 at the Ecological Benefit Monitoring Station of the Yangtze River Protection Forest in Cili County,Hunan Province(29°30′N,110°10′E),which were aggregated to assess the law of canopy hydrology.Results showed that rainfall redistribution of canopy in the E.ulmoides forest was closely related to precipitation characteristics.Throughfall,interception and stemflow of E.ulmoides positively correlated with rainfall depth(P0.05).As rainfall depth and intensity increased,throughfall percentage of gross rainfall increased,but interception percentage of gross rainfall decreased.And throughfall and interception percentages of gross rainfall stabilized at larger rainfall depths.Over the whole measurement period,throughfall,stemflow and interception percentages of gross rainfall were 72.7±7.8%,7.7±1.8% and 19.6±9.9%,respectively.Throughfall below the canopy had clearly spatial heterogeneity and throughfall percentage of gross rainfall at positions closest to the trees was lower than those under the peripheral part.With increasing the distances between sampling site and stem,throughfall percentage of gross rainfall gradually increased.Moreover,the spatial variation in throughfall(i.e.,CV of throughfall percentage of gross rainfall) decreased with increasing rainfall depth.Stemflow volume per mm of rainfall per stem(cm~3·mm~(-1)) was positively correlated with diameter at breast height,crown depth and tree height(P0.05).However,stemflow was not significantly related to crown diameter? and height from the base to the first branch(P0.05).For the components of sub-canopy rainfall,the ratio of stemflow(SF) to throughfall(TF) decreased with increasing rainfall intensity or rainfall depth.Stemflow of E.ulmoides can evidently concentrate water into a small area around the tree trunk and the funneling ratio(FR) increased gradually,reached its peak at rainfall depth of 75.9 mm and then decreased with increasing rainfall depth. Although canopy interception decreased sub-canopy rainfall input,canopy of E.ulmoides forest also altered spatial distribution of sub-canopy rainfall synchronously and the input rainfall amount near the stem was higher than those outside of forest.