Bidin, K., and Chappell, N.A. 2004. Sub-canopy rainfall and wet-canopy evaporation in a selectively-logged rainforest, Sabah, Malaysia. In Water: Forestry and Landuse Perspectives, A. R. Nik (Ed), IHP-VI Technical Document in Hydrology No. 70, Paris, UNESCO. p69-85. ISBN 9292200305. view technical document (pdf)

 

Understanding the impact of the selective removal of trees from a tropical rainforest on the rate of wet-canopy evaporation and transpiration is critical to the assessment of the impact of so called 'sustainable forestry' on local climate, and the water resources potential of rivers. Accurate quantification of the changes in the wet-canopy evaporation component is, however, difficult given the extreme heterogeneity of the vegetation patchwork produced by commercial, selective logging.

In order to address this issue for an area of lowland dipterocarp forest, selectively-logged some eight years prior to the study, a network of 450 throughfall gauges, plus 22 gross rainfall and 40 stemflow gauges, was installed within the 44-hectare Baru Experimental Catchment (Sabah, Malaysian Borneo). Most of these gauges were located randomly within plots, themselves stratified according to the six canopy classes.

The results showed that more rainfall reached the forest floor beneath the undisturbed remnants of rainforest (i.e. the protected areas), than those patches of canopy subject to light or heavy impact. This may have been because the disturbed forest patches had a higher rate of wet-canopy evaporation (i.e.12-18 % of gross rainfall) in comparison to the undisturbed remnants (i.e. 7% of gross rainfall). Alternatively, the difference may, at least in part, have been caused by the lower disturbed patches of vegetation being sheltered by the undisturbed forest remnants, leading to the receipt of less rainfall on their canopy surfaces.

 

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