Spatial variability of throughfall in a subtropical rain forest in Taiwan

Eight rainfalls were intensively sampled in a subtropical rain forest in northeastern Taiwan. This study, carried out at Fu-shan Experimental Forest was designed to examine variability of throughfall characteristics. The volume and chemistry of the throughfall associated with individual rains have a high degree of spatial variability, with throughfall chemistry more variable than volume. When data from all of the storms were combined, there was lower variability than that seen with individual storms, largely as a result of a lack of consistent storm to storm spatial variation. Thus, individual storms cannot be used to represent the seasonal or annual pattern of spatial variation in throughfall chemistry or volume of the study forest. Twenty samples were required to estimate throughfall volume within 10% of the population mean with 95% confidence for individual storms. Yet, more than 100 samples were required to estimate the throughfall chemistry of some ions (e.g., H⁺). When the data from all eight storms were combined, 7, 20, and 25 samples were necessary to estimate throughfall volume, ion concentrations, and ion fluxes (except for Mg²⁺ and H⁺) within 10% of the population mean with 95% confidence. In the absence of estimates of spatial variation, differences in sampling protocols among throughfall studies make comparisons of throughfall characteristics difficult. In this study three funnels were used in tandem to capture small scale variability at each sample location, thus reducing spatial variability of throughfall chemistry.