Partitioning rainfall into throughfall, stemflow, and interception loss in an oriental beech (Fagus orientalis Lipsky) forest during the growing season

Partitioning gross rainfall (GR) into throughfall (TF), stemflow (SF), and interception loss (I), which has a very significant effect on water balance and the nutrient cycle in forest ecosystems, was studied in a natural oriental beech (Fagus orientalis Lipsky) forest situated in the Caspian Forest of northern Iran. Measurements were made inside a plot with an area of 0.5625 ha located in the Kheyrud Forest Research Station of Tehran University during the 2008 growing season. GR was measured based on an average of the records of 3 rain gauges located in an open area approximately 160 m from the study plot. Thirty-six TF manual gauges were randomly placed beneath the beech canopies and SF was collected from 6 selected beech trees using spiral-type SF collection collars. Measurements were made on a rainfall event basis. The cumulative GR depth of 23 events was 309.9 mm; TF: 209.9 mm; SF: 7.8 mm; I: 92.2 mm. On the event scale average ratios of TF:GR, SF:GR, and I:GR were 65.9%, 2.0%, and 32.1%, respectively. A strong positive correlation was observed between SF:GR and GR (r2 = 0.963), while very weak correlations were observed between I:GR and GR (r2 = 0.230), and between TF:GR and GR (r2 = 0.173). As the size of rainfall events increased, intercepted GR by the oriental beech forest canopies, and loss through evaporation decreased. Interception loss contributes a notable amount of rainfall and its measurement is an essential element in assessing water balance on the catchment scale.