Path Analysis on Environmental Factors Controlling Runoff and Sediment Yields in Shelter Forests in Three Gorges Reservoir Region

Effects of environmental factors such as climate, topography, vegetation and soil in shelter forests in Three Gorges Reservoir Region on runoff and sediment yields were monitored to identify dominant environmental factors controlling runoff and sediment yields in 15 runoff plots in study area by soil sampling, laboratory analysis, stepwise regression analysis and path analysis, and to establish the main control environmental factors that affect runoff and sediment yields. The results showed that soil bulk density, herbaceous cover, slope, and canopy density were the significant factors controlling runoff, and the direct path coefficient of each factor was ranked as canopy closure (-0.628) > litter thickness (-0.547) > bulk density (0.509) > altitude (0.289). The indirect path coefficient was ranked as soil bulk density (0.354) > litter thickness (-0.169) > altitude (0.126) > canopy closure (-0.104). Therefore, canopy closure and litter thickness mainly had direct effects on runoff, while soil bulk density mainly had indirect effects through their contributions to other factors. Herbaceous cover, litter thickness, slope, canopy density, and altitude were the significant factors controlling sediment yields. The direct path coefficient of each factor was ranked as herbaceous cover (-0.815) > litter thickness (-0.777) > canopy closure (-0.624) > slope (0.620). The indirect path coefficient was ranked as slope (0.272) > litter thickness (-0.131) > canopy closure (-0.097) > herbaceous cover (-0.084). Therefore, herbaceous cover and litter thickness mainly had direct effects on sediment yields, while slope mainly had indirect effects through their contributions to other factors. All the selected environmental factors jointly explained 85.5% and 78.3% of runoff and sediment yield variability, respectively. However, there were large values of remaining path coefficients of other factors influencing runoff and sediment yields, which indicated that some important factors are not included and should be taken into account.