Spatial variability of throughfall in aPinus tabulaeformisplantation forest in Loess Plateau, China

Throughfall varies in space, which complicates measurements and makes it difficult to achieve accurate spatial representation. In the present research, we measured gross rainfall and throughfall from May 2011 to September 2012, leaf area index, and locations of trees within a Pinus tabulaeformis plantation forest in the Loess Plateau of northwestern China. The spatial heterogeneity of throughfall and related factors, as well as the minimum number and locations of collectors needed to measure throughfall accurately, were analyzed by statistical techniques. The results indicated that the throughfall was concentrated at the canopy edge, indicating that the edge of the canopy of P. tabulaeformis had a convergence effect on throughfall. The analysis of semivariance of throughfall demonstrated that canopy structure was a key factor influencing spatial variation of throughfall in low rainfall events, but measurement errors and other nonspatial variables were the primary factors affecting the variation of throughfall in high rainfall events. Based on the mean throughfall at different proportions of canopy radius centered on the individual tree stem, the minimum number and locations of collectors needed to accurately measure throughfall was estimated. In this study, four rain collectors (diameter 20 cm) at the 3/5 canopy radius could reasonably represent the average throughfall under the individual P. tabulaeformis canopy.