The role of Quercus castaneifolia C.A.M forest canopy on redistribution of summer rainfall

Measurements of gross rainfall (GR)، throughfall (TF)، and stemflow (SF) were conducted during the summer 2009 beneath a natural pure stand of oak (Quercus castaneifolia C. A. M) forest canopy located near the southern border of Kheyrud Forest Station of Tehran University. Measurements were made inside a plot with an area of 0. 12 ha. GR was collected by means of three manual collectors placed in a neighboring open area away from the study plot. Thirty five TF manual collectors were randomly positioned underneath the tree canopies. SF was collected from nine oak trees with different diameters by the spiral-type SF collection collars installed at diameter at breast height. All the measurements were performed on a rainfall event basis using a graduated cylinder. Interception loss (I) was calculated indirectly as the differ rence between GR and the sum of TF and SF. During the study period، 10 events were recorded. The cumulative GR، TF، SF، and I depths were 257 mm، 192 mm، 0. 7 mm، and 64. 3 mm، respectively. At the event scale average ratios of TF: GR، SF: GR، and I: GR were 72. 2%، 0. 2%، and 27. 6%، respectively. A weak correlation was observed between SF: GR and GR (r2 = 0. 43) while a fairly strong positive correlation was observed between I: GR and GR (r2 = 0. 65). Interception loss contributes a remarkable amount of incident rainfall in the studied oak forest and its measurement is an essential element in assessing water balance on a catchment scale.