Rainfall Redistribution by an Oriental Beech (Fagus orientalis Lipsky) Forest Canopy in the Caspian Forest, North of Iran

Gross rainfall (GR) partitioning into throughfall (TF), stemflow (SF) and interception loss (I) was studied in a pure oriental beech (Fagus orientalis Lipsky) forest located in the central Caspian region of northern Iran. Measurements were performed on a rainfall event basis in a 5625 m2 plot of the Kheyrud Forest Research Station of Tehran University during 2008 and 2009 growing seasons. GR was measured with three rain gauges located on the ground in an open area approximately 160 m apart from the study plot. Thirty-six manual gauges were used to collect the TF and were placed randomly underneath the canopy. SF was collected with spiral type SF collection collars from six selected beech trees. Interception losses were calculated as the difference between GR and the sum of TF and SF. Over the measurement period, 53 GR events were recorded. Cumulative GR depth was 1,001.5 mm; TF amount was 728 mm; SF was 32.3 mm, and I was 241.2 mm. The average of TF/GR, SF/GR, and I/GR ratios for each rainfall events were 69.4%, 2.5% and 28.1%, respectively. TF, SF, and I were found to be closely related to GR amounts. A strong positive correlation was found between SF/GR and GR (R2= 0.9). Significant correlations were also observed between I/GR and GR (R2= 0.581) as well as between TF/GR and GR (R2= 0.414). It was observed that for small GR events a large portion of the incident GR wetted the canopy and, subsequently, contributed to the evaporation losses of the intercepted rain. Results of the study demonstrate how I represents a remarkable percentage of the incident GR and how TF and SF are both strongly affected by GR itself.