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Leaflet
LE0113-08
TitleDeforestation and the multiple functions of tropical watersheds: are tropical forests indispensable for regulating rainfall and ensuring clean and reliable water supplies?
AuthorMeine van Noordwijk and Sampurno Bruijnzeel
Year2008
PublisherASB Partnerships for the Tropical Forest Magins
CityNairobi, Kenya
Call NumberLE0113-08
Abstract:
1. Are all forests alike ?

Natural forests are ecosystems, not mere collections of trees. Several features of natural forest – its rough surfaces, swamps and other temporary water storage sites make it more able to regulate water flow than a man-made forest.

2. Does forest produce extra rain?

There is evidence that large-scale removal of tropical forest in humid parts of the world affects rainfall during the transition between rainy and dry season. However, effects on annual rainfall are modest (5-10%) relative to inter-annual variability.

3. Does forest affect annual water yield?

Removal of forest initially increases annual water yield. The type of vegetation that follows and the degree of soil compaction determines the water yield in subsequent years.

4. Does forest reduce flooding?

The presence or absence of forests in upland watersheds is not a key contributing factor to the major floods that draw most policy and media attention. However, there is ample evidence that forest cover does affect timing and intensity of floods in small catchments.

5. Does forest reduce erosion, landslides and stream sedimentation?

Forest conversion to other land uses without proper soil conservation measures increases hillslope soil erosion and the risk of shallow landslides.
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GRP 6: Developing policies and incentives for multifunctional landscapes with trees that provide environmental services
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