Abstract
An important component of the water cycle in ecological systems, rainfall interception by virgin forests was here calculated from gross precipitation minus through fall and stem flow. The through fall measurement system was designed on the basis of a 3 m long trough mounted beneath the canopy and able to operate successfully under a range of rainfall conditions. Stem flow was measured using spiral collars consisting of a split plastic hose attached to sampled trees, with gross precipitation measured in an open area via a tipping-bucket rain gauge. This study was carried out to evaluate rainfall interception and distribution patterns of gross precipitation in two contrasting rainforest types (coniferous and broadleaved/coniferous mixed) in the Mount Gongga area on the eastern fringe of Tibet, China, from 2008 to 2009. Net precipitation was found to be primarily composed of through fall, while stem flow contributed less than 0.5% (0.1% and 0.4% in conifer and mixed forest, respectively) to total gross precipitation (GP) and was thus negligible in both forest types. The difference in the interception loss fraction between conifer and mixed forest was greater than 30%, with the interception loss of the former apparently more than that of the latter mainly due to the increased presence of small droplets produced by coniferous leaves. Additionally, interception loss in conifer forest was more dependent on rainfall than that in mixed forest. In contrast, through fall and stem flow exhibited the opposite pattern, likely attributable to a through fall lag of 8 to 10 h after rainfall in mixed forest but not in conifer forest.
Highlights
Rainfall interception is believed to play an important role in the water balance of catchments and plant ecosystems
A substantial correlation between rainfall and interception was observed at both sites, interception loss varied distinctly between the two forest types
The present study revealed interception loss to be more dependent on rainfall in the conifer than in the mixed forest (Figures 3 and 4)
Summary
Rainfall interception is believed to play an important role in the water balance of catchments and plant ecosystems. An essential component of forest water balance is the interception of rainfall by the canopy and its subsequent evaporation to the atmosphere. The amount of water intercepted by and evaporated from a forest canopy (interception loss (IE)) can be estimated by calculating the difference between gross (above canopy) and net (below canopy) precipitation, the latter being the sum of through fall (TF) and stem flow (SF) [1]. In temperate forests [4], interception loss ranges from 9% to 48% of gross precipitation, is influenced by canopy structure, and is widely reported to account for 10-40% of annual rainfall [5]. David et al [1] reported interception loss to represent 22% of gross rainfall in a Mediterranean savannah; Link et al [6] recorded values of 22.8% and 25.0% of gross rainfall in temperate rainforest in 1999 and 2000, respectively. The annual interception loss measured in five forest transects varied from 25% to 52% of incident rainfall in tropical montane forests [8], whereas apparent annual rainfall interception losses were 7.7% and 29.6% of gross precipitation in upper and lower tropical montane forests in the eastern Andes of Central Peru, respectively [9]
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