Temporal Stability of Throughfall Spatial Pattern under Individual Oak Trees in the Zagros Region (Case Study: Neighboring Forests of Ilam)

Spatio-temporal variability of throughfall (TF) has an important role on the biogeochemical processes, soil, watershed hydrology as well as the nutrient cycle in forests. Spatial distribution and temporal stability of TF patterns by five individual Persian oak trees (Quercus brantii var. Persica) in the Zagros forests of western Iran, Ilam, was quantified. Sixteen TF manual gauges were placed beneath the five selected tree canopies in the eight geographic directions and the gross rainfall (GR) was measured by the mean of six homemade gauges records placed in an open area adjacent to the study site. Rainfall interception (I) was indirectly estimated as the difference between GR and TF. The measurements were recorded during three months from end of December 2010 to beginning of April 2011. During this period, 24 rainfall events with cumulative depth of 302.4 mm was collected, of which on average 14.3% evaporated as I or expended as canopy storage by individual Persian oak trees. Less than 6% of sampling points in the time stability plots deviated consistently (α= 0.05) from the mean normalized TF, meaning lower heterogeneity of TF compared to other studies on the forest stands. Moreover, generally ranking of TF collectors of time stability plots confirmed lower TF concentrations near the tree trunks for individual Persian oak trees. Time stability plots in the current study were appeared a useful tool to quantify TF distribution of individual Persian oak trees.