Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

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Impacts of forestation on water and soils in the Andes: what do we know?

Abstract

This infobrief presents findings on the impacts of forestation on: (1) water supply; (2 and 3) hydrological regulation; and (4) soil erosion in the Andes. It is established that exotic tree plantations and, to a lesser extent, native forests consume water and therefore often reduce the total water supply to downstream users in most Andean regions. Only in areas immersed in clouds, such as in the eastern slope of the Andes, might native forests increase downstream water availability compared to other land covers. Decreased total water supply could be acceptable to many users if it confers other benefits, such as increased water availability during the dry season or a reduction in water turbidity. When trees, including exotic species, are planted on degraded soils (bare and/or compacted soils), they can improve soil infiltration, reduce peak flows and control erosion. Exotic tree plantations on well-conserved grasslands (páramos, jalcas, punas) have detrimental impacts on total water supply and hydrological regulation. Existing native forests provide excellent water regulation and erosion control, more than mature tree plantations. As restoring degraded native forests does not necessarily recover original hydrological services, the conservation of existing forests must be a priority for watershed management.