Some Statistical Aspects of Sampling Throughfall Precipitation in Nutrient Cycling Studies in British Columbian Coastal Forests

Abstract

The number of fixed collectors required to sample the volume and cation content of throughfall precipitation in the coastal forests of British Columbia was examined by means of data from 134 collectors for throughfall volume and 83 collectors for throughfall chemistry. The relative heterogeneity of throughfall parameters in four forest plant associations was also examined. It was concluded that a sampling network suitable for quantifying throughfall volume will be inadequate for quantifying throughfall chemical parameters be· cause of the far greater spatial variability of the latter. This variability is compounded if the study area includes more than one forest plant association. The fixed-collector method was found to be far from ideal for accurate studies of the role of leaching in nutrient cycling because of the excessive number of collectors required. An analysis of the suitability of Wilm's method of roving collectors and Attiwill's modification thereof as alternatives indicated that Wilm's method is inapplicable to studies of throughfall chemistry, but that Attiwill's modification might permit a worthwhile reduction in the number of collectors required in some studies, especially those concerned with gross, long-term studies of leaching. Attiwill's method shares many of the drawbacks of Wilm's method, however, and will probably be unsuitable for many studies.The variability of the chemical data was greatest when expressed as concentrations. Conversion to kg/ha did reduce standard deviations somewhat, although the reduction was modest on all but the most highly variable study area. Sampling at longer intervals did not result in any reduction in the standard deviations of mean throughfall cation concentrations: the effect of longer collection periods on the data expressed as kg/ha was to increase standard deviations significantly. Weekly or more frequent collections are recommended for detailed studies of throughfall chemistry.

The dynamics of rainfall interception by a seasonal temperate rainforest

“…Using a large number of gauges samples across the range of variability (Kimmins, 1973;Kostelnik et al, 1989;Puckett, 1991), and periodically moving gauges further increases the effective number of sampling points within the plot to reduce errors in throughfall sampling by increasing the number of sampling points within the plot Wilm, 1943). The array of automated gauges was used to measure interception losses and to derive canopy interception parameters for individual events, and the manual gauge array was used to measure the interception losses over extended periods for model validation.…”

Spatial variability of throughfall water and chemistry and forest floor water content in a Douglas fir forest stand

“…Both throughfall water and ion fluxes and forest floor water contents have a high spatial and temporal variability. A number of studies has addressed the spatial variability of throughfall (Kimmins, 1973;Robson et al, 1994) and the distribution of throughfall, both ions and water, has been related to the distance from a tree stem (Beier et al, 1993;Pedersen, 1992;Whelan et al, 1998). Generally, for coniferous forests, concentrations and fluxes of ions decrease and water fluxes increase with distance from the tree stem.…”

Stemflow and throughfall determination in a resprouted Mediterranean holm-oak forest

“…The role of the canopy in the redistribution of precipitation inputs to the forest soil has been well studied in both temperate and tropical ecosystems ([1, 2, 16,20,21,22,24,32,37,38,41], and many other studies). Most of these papers emphasize the importance of throughfall as the major water flow on aboveground vegetated surfaces in the canopy.…”