Rainfall redistribution in natural pure stands of Quercus castaneifolia C.A.M. and Fagus orientalis L. in Caspian forests (Case study: Kheyrud forest)

Measurements of gross rainfall (GR), throughfall (TF), and stemflow (SF) were conducted inside oriental beech (Fagus orientalis Lipsky) and oak (Quercus castaneifolia C.A.M.) forests in Kheyrud Forest Station of University of Tehran. GR was collected by means of three manual collectors placed in neighboring open areas from the study plots. TF was collected by thirty five TF manual collectors positioned randomly underneath the trees canopies. SF was collected from beech and oak trees, with different diameters by the spiral-type SF collection collars installed at diameter at breast height. Rainfall interception (I) was calculated indirectly as the difference between GR and sum of the TF and SF. The cumulative GR depths of 13 and 14 events for oak and beech forests were 297 and 270 mm, respectively. On the event scale average ratios of TF:GR, SF:GR, and I:GR in the oak forest were 75.50%, 0.26%, and 24.24%, respectively, whilst those of the beech forest were 71.30%, 2.70%, and 26%. Strong positive correlations were observed between ‏TF and GR in both oak and beech forests. Results showed fairly strong negative relationships between I:GR and GR in both forests. Rainfall interception contributes a notable amount of incident rainfall in the oak and beech forests and its measurement, therefore, is an essential element while assessing water balance on the catchment scale.