Tree plantation in South America and the water cycle: Impacts and emergent opportunities

JOBBÁGY, ESTEBAN G.; BALDI, GERMÁN; NOSETTO, MARCELO D.

Forests in Development: A Vital Balance

Springer

Año: 2012; p. 53 - 63

South American tree plantations expand at a rate of 5,000 km2/year favored by increasingly globalizedmarkets and local economic conditions. The main hydrological impacts of these plantations involve shiftsin (a) the partition of precipitation inputs between vapour vs. liquid fluxes (associated to transpirationand canopy interception shifts) and (b) the partition of liquid fluxes between run-off and fast flow vs.deep drainage and base flow (associated to infiltration and surface water routing shifts). In sloped terrainsglobal stream flow measurements in paired watersheds indicate declining water yields (40% less onaverage) under plantations vs. native vegetation. These effects are stronger under drier climates, wherehost vegetation is herbaceous, and where planted trees are eucalypts. In flat landscapes with nativegrassland 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 woodlandtree plantation can remediate the undesirable recharge and water table rise/salinization problems broughtby agriculture. In degraded rolling (sub)tropical landscapes with intense rainfall inputs and high run-off,tree plantations can increase infiltration rates, reducing erosion, stabilizing flow, but cutting total wateryield. As a result of these shifts, erosion can be reduced and the stability and quality of water provisionimproved, yet these benefits can be erased by large scale clear cutting practices. Context (climate, currentvegetation 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 thebest ecological outcome of afforestation in the continent.