Factors controlling throughfall in a Pinus tabulaeformis forest in North China

The factors that control throughfall in Pinus tabulaeformis plantations were investigated using linear and curve analyses based on direct measurements of rainfall, throughfall and stemflow from 36 rainfall events. The results showed the following: (1) there was significant spatial heterogeneity in throughfall rates in P. tabulaeformis plots; (2) the throughfall rate increased with increasing rainfall; and (3) the rate of increase gradually decreased. When rainfall reached approximately 25 mm, the throughfall rate stabilized. The coefficient of variation of the throughfall rate decreased with increasing rainfall, with a peak at approximately 10 mm of rainfall. The coefficient of variation of throughfall stabilized at 20%, and the coefficient of variation of the throughfall rate stabilized at 17%. A linear regression equation (R² = 0.76) was derived by fitting the P. tabulaeformis average diameter at breast height (DBH), average tree height, average branch height, stand density, canopy thickness, canopy density, and the rainfall and throughfall rate. A highly positive correlation was found between the throughfall rate, canopy density, rainfall class and tree height (P < 0.01). By establishing a quadratic response surface model of the stand structure indicators and the throughfall rate, R² was increased to 0.85 (P < 0.01). The quadratic regression analysis demonstrated a highly positive correlation between throughfall rate, canopy density and rainfall class.