Middle-East Journal of Scientific Research 13 (7): 876-882, 2013 ISSN 1990-9233 © IDOSI Publications, 2013 DOI: 10.5829/idosi.mejsr.2013.13.7.2721 Corresponding Autor: Mohammad Taghi Ahmadi, Member of Young Researchers Club, Karaj Branch, Islamic Azad University, Karaj, Iran. Tel: +98-9362777533. 876 The Role of Rainfall Size in Canopy Interception Loss: An Observational Study in a Typical Beech Forest Mohammad Taghi Ahmadi, Pedram Attarod and Vilma Bayramzadeh 1 2 3 Member of Young Researchers Club, 1 Karaj Branch, Islamic Azad University, Karaj, Iran Department of Forestry and Forest Economics, 2 Faculty of Natural Resources, University of Tehran, Karaj, Iran Department of Soil Sciences, Karaj Branch, Islamic Azad University, Karaj, Iran 3 Abstract: Canopy interception loss (I) is the fraction of the gross rainfall (GR) that intercepted by forest canopy and subsequently evaporated; it does not reach the forest floor. I is commonly calculated indirectly as the difference between GR and net rainfall (NR i.e. sum of the throughfall (TF) and stemflow (SF)). The goal of the present study was to understand the role of GR size in controlling the I in an oriental beech (Fagus orientalis Lipsky) forest located at the midland of the central Caspian forests. Measurements were carried out on a rainfall event basis in a 0.5625 ha sample plot of a pure oriental beech forest in the Kheyrud Forest Research Station of Tehran University. GR was measured based on an average of three rain collector records placed in an open area close to the study plot. Thirty six TF manual collectors were randomly placed beneath the beech canopies and SF was collected from six selected beech trees using the spiral type SF collection collars. During the measurement period, from June 2008 to November 2009, a total of 53 rainfall events were recorded. The mean rainfall events was 18.9 mm (SD: ±11.8 mm) ranging from 2.8 to 48.6 mm. The amount of cumulative GR depth transformed into NR was 760.3 mm (75.9% of GR) and the remaining, 241.2 mm or 24.1% of GR, was intercepted by the canopies and subsequently returned to the atmosphere. At the event scale average ratio of I/GR was 28.1% (SD: ±8.8%). Regression analysis suggested a strong positive power correlation between I and GR (r = 0.817; p 0.01), while a fairly strong negative exponential correlation was observed between I/GR and GR 2 (r = 0.581; p 0.01). As the size of the rainfall events increased, intercepted GR or I/GR by the oriental beech 2 forest canopy and loss through evaporation decreased. We concluded that I in an oriental beech forest contributes a remarkable percentage of incident GR and it was strongly affected by the amount of GR. Key words: Interception loss Fagus orientalis Lipsky Net rainfall Stemflow Throughfall INTRODUCTION evaporated; it does not reach the forest floor [1]. I is In forest ecosystems gross rainfall (GR) is partitioned GR measured above the canopy or in a neighboring open into throughfall (TF), stemflow (SF) and interception loss area and the sum of the TF and SF sampled (I). Net rainfall ( NR) reaches the forest floor through the simultaneously on the forest floor [2]. canopy via SF and TF. The TF is the portion of rainfall The interactions between vegetation and rainfall that reaches the forest floor by passing directly through are of considerable significance from the physiological, or dripping from tree canopies. The SF is the fraction of ecological and hydrological points of view. In particular, the rainfall that reaches the forest floor by running down rainfall partitioning by forest canopies plays an important the stems of trees after the incident rainfall is intercepted role in water balance on the local and catchment by leaves and branches and is subsequently diverted to scales due to the control that forest canopies exert by the boles of trees. The I is the fraction of the incident modifying both evaporation and the redistribution of rainfall intercepted by the canopy and subsequently incident rainfall [3]. commonly measured indirectly as the difference between