Throughfall and throughfall spatial variability in Madrean oak forest communities of northeastern Mexico

Point throughfall data were generated in two representative red oak stands of a small Madrean watershed in northeastern Mexico during the 2000 and the 2001 wet seasons. Cumulative gross precipitation for 18 selected events was 392.9 mm, while the mean cumulative point throughfall flux from 38-fixed gauges was 331.0±9.0 mm (84.2±2.3%). The influence of canopy and understory cover fraction, vegetation area index (VAI), distance to nearest tree bole, as well as the basal area and height of that tree may have on point throughfall depth were evaluated. No significant (α=0.05) relationship between point throughfall and these stand characteristics could be established for gross precipitation inputs >5 mm. However, excluding events in which occult precipitation was thought to contribute to throughfall generation, the spatial distribution of throughfall was found to be a function of at least one of these factors during each of the gross precipitation inputs <5 mm. For gross precipitation events >5 mm point throughfall for all but one event did not significantly deviate from the normal distribution, suggesting that stand-scale throughfall fluxes associated with these relatively larger events may be estimated from a random array of gauges. An average of 9 (range=3–14) and 34 (range=11–54) gauges would have been required to estimate mean event throughfall input to the red oak forest floor to within ±10 and ±5% at the 95% confidence level, respectively, for gross precipitation events >5 mm.