Tree Plantation in South America and the Water Cycle: Impacts and Emergent Opportunities

T. Schlichter and L. Montes (eds.), Forests in Development: A Vital Balance, DOI 10.1007/978-94-007-2576-8_5, © Springer Science+Business Media B.V. 2012 Abstract South American tree plantations expand at a rate of 5,000 km 2 /year favored by increasingly globalized markets and local economic conditions. The main hydrological impacts of these plantations involve shifts in (a) the partition of precipitation inputs between vapour vs. liquid fl uxes (associated to transpiration and canopy interception shifts) and (b) the partition of liquid fl uxes between run-off and fast fl ow vs. deep drainage and base fl ow (associated to infi ltration and surface water routing shifts). In sloped terrains global stream fl ow measurements in paired watersheds indicate declining water yields (40% less on average) under plantations vs. native vegetation. These effects are stronger under drier climates, where host vegetation is herbaceous, and where planted trees are eucalypts. In fl at landscapes with native grassland vegetation, tree plantations switch the water balance from positive (net recharge) to negative (net discharge) triggering local salinization. Contrastingly, where native vegetation has been a woodland tree plantation can remediate the undesirable recharge and water table rise/salinization problems brought by agriculture. In degraded rolling (sub)tropical landscapes with intense rainfall inputs and high run-off, tree plantations can increase infi ltration rates, reducing erosion, stabilizing fl ow, but cutting total water yield. As a result of these shifts, erosion can be reduced and the stability and quality of water provision improved, yet these benefi ts can be erased by large scale clear cutting practices. Context (climate, current vegetation and topography/geology) and design (species, densities, harvesting methods, and scale/pattern) can decide the magnitude and sign of tree plantations effects and need to be carefully considered to get the best ecological outcome of afforestation in the continent.