Throughfall variation in a mixed deciduous forest

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Virginia Polytechnic Institute and State University


Gross rainfall and throughfall were measured in an uneven-aged, mixed deciduous forest in western Virginia from August 6, 1972 to June 19, 1973. Storms were grouped according to leafy (growing) season and leafless (dormant) season for analysis of gross rainfall and throughfall. Average leafy season throughfall was 78.2 percent of gross rainfall, and leafless season throughfall was 81.86 percent.

Regression of throughfall on gross rainfall explained approximately 99 percent of variation in throughfall. Variations in throughfall were also related to storm characteristics, irregularities of vegetative cover, and different concentrations of throughfall at single sampling positions. Coefficients of variation decreased with increasing amounts of gross rainfall.

Throughfall amounts increased with decreasing canopy density over plots. However, an analysis of variance showed no significant differences of mean throughfall among plots. Throughfall caught in several gauges exceeded gross rainfall in 36 of 40 storms. This phenomenon was more pronounced in the leafy season. There was relatively little difference in throughfall between seasons.

Soil moisture was determined on two dates. No correlation could be demonstrated between soil moisture distribution and throughfall under the forest canopy. The results, however, were inconclusive, owing to the small number of samples taken.