Throughfall variability in a southern Illinois broadleaved deciduous forest

Forests are a critical component of the hydrologic cycle and act as an important intermediary between precipitation and the land surface. Precipitation reaching a forest canopy can be partitioned into throughfall (precipitation falling through the canopy with or without contacting a vegetative surface), stemflow (precipitation flowing down the trunk of a tree), or may be intercepted. As a macro-scale process in forested ecosystems, throughfall plays a significant role in the hydrologic and biogeochemical cycles at local, regional, and global scales. Throughfall is inherently variable in time and space, and increased knowledge of this variability is crucial to furthering the understanding of throughfall and processes dependent upon it.;To evaluate throughfall variability in a deciduous forest at the plot scale, throughfall data were collected for 30 events using 24 gauges fixed to a 5.0 m2 grid. Throughfall inputs were found to be highly variable at the plot scale, both within and between events. Individual catch varied as much as five times between gauges within the plot and four times between neighboring gauges during a single event. Differences between dormant and growing season events were significant for throughfall as a percentage of gross precipitation, but variability was only slightly greater during the growing season. The large amount of variability over plot scale distances may be significant for scientists concerned with processes influenced by throughfall inputs such soil moisture and biogeochemical fluxes. The traditional metric, coefficient of variation, used in evaluating throughfall variability may be undesirable in quantifying this variability, as it is considerably unstable at low mean values. The author suggests the use of the mean absolute deviation to better quantify throughfall variability. Additional considerations for improving the understanding of throughfall variability are presented.