Improving water quality and quantity is sometimes cited as motivation for restoring and expanding forest cover, especially in the tropics. But a new systematic review of literature finds that most studies show a reduction in water yield in response to forest restoration and expansion.
The study was a collaborative effort led by Associate Research Professor Solange Filoso at the University of Maryland’s Center for Environmental Science (UMCES), and several researchers from SESYNC, including SESYNC Director Margaret Palmer, Kate Weiss, computational research assistant and Maíra Ometto Bezzera, a graduate research assistant at SESYNC and UMCES.
The researchers looked at the results of over 300 case studies from around the world and found that about 80% reported negative water yields in response to forest restoration and other forms of forest cover expansion.
Filoso et al. 2017, PLoS ONE: Fig 11. Geographic location of study cases and their water yield outcomes.
While this systematic review has confirmed the consensus shared by many forest hydrologists and other scientists -- that the restoration of forest cover/area does not result in an increase of the annual water yield -- the researchers point out that there are shortcomings in the studies available in the literature to date, which limit their capacity to predict the outcome of restoration in the long run and at the large scale.
"The review shows that studies available rarely include restoration with native species, especially in the tropics and subtropics," said Professor Solange Filoso. "The conclusion was that we need more studies that are properly designed (i.e. long term, large scale, with native species and control sites) to better understand the recovery of hydrologic processes in restored forests and, consequently, advance knowledge about the effects of forest restoration on water. This kind of information is needed to guarantee that forest restoration will result in the recovery of important ecosystem services without unintended consequences."
The review uncovered some positive impacts of forest restoration and expansion: reduced flood frequency and improved water infiltration into soils. These services could improve water management and mitigate flooding risk in times of high precipitation.
Read the paper in PloS ONE: Impacts of forest restoration onwater yield: A systematic review