Impacts of forest restoration on water yield: A systematic review

Abstract

BackgroundEnhancing water provision services is a common target in forest restoration projects worldwide due to growing concerns over freshwater scarcity. However, whether or not forest cover expansion or restoration can improve water provision services is still unclear and highly disputed.PurposeThe goal of this review is to provide a balanced and impartial assessment of the impacts of forest restoration and forest cover expansion on water yields as informed by the scientific literature. Potential sources of bias on the results of papers published are also examined.Data sourcesEnglish, Spanish and Portuguese peer-review articles in Agricola, CAB Abstracts, ISI Web of Science, JSTOR, Google Scholar, and SciELO. Databases were searched through 2015.Search termsIntervention terms included forest restoration, regeneration/regrowth, forest second-growth, forestation/afforestation, and forestry. Target terms included water yield/quantity, streamflow, discharge, channel runoff, and annual flow.Study selection and eligibility criteriaArticles were pre-selected based on key words in the title, abstract or text. Eligible articles addressed relevant interventions and targets and included quantitative information.ResultsMost studies reported decreases in water yields following the intervention, while other hydrological benefits have been observed. However, relatively few studies focused specifically on forest restoration, especially with native species, and/or on projects done at large spatial or temporal scales. Information is especially limited for the humid tropics and subtropics.Conclusions and implications of key findingsWhile most studies reported a decrease in water yields, meta-analyses from a sub-set of studies suggest the potential influence of temporal and/or spatial scales on the outcomes of forest cover expansion or restoration projects. Given the many other benefits of forest restoration, improving our understanding of when and why forest restoration can lead to recovery of water yields is crucial to help improve positive outcomes and prevent unintended consequences. Our study identifies the critical types of studies and associated measurements needed.

Previous Land Use Affects the Recovery of Soil Hydraulic Properties after Forest Restoration

“…This result was directly related to the highest ρ b found in the study pastures, which influences the higher soil Mic and lower soil Mac values [65]. Similar findings have been reported be several authors [13][14][15]. An exception to this was related to pasture plot P1D, which showed similar K s values compared to the restored forest and remnant forest in the sandy loam texture, suggesting lower soil compaction, and consequently higher soil Mac.…”

“…Moreover, the present results illustrate the K s spatial variability in two different pasture sites, characterized by a low variation in K s values. This could be due to the soil compaction [4,13], and the duration of pasture use in the land-use history, which is one of the most important factors for K s variability over time [15,17], as well as the cattle-grazing intensity that could have influenced the K s variability in the pasture plots [7]. Moreover, the lower soil faunal activity and organic matter in pasture land covers are important factors when analyzing the soil attributes [15,56].…”

“…The present results agree with several studies [4,16,23], which suggest that K s decreases with increasing land-use intensity, and that K s recovery will be longer in view of the intensive land use. Filoso et al [13] argued that in some cases the recovery of soil infiltration after forest restoration may be extremely difficult, because of the absence of natural understory vegetation. This research did not directly quantify the herbaceous cover, but in the field we observed that natural regeneration in the restored forest R4 is impeded by the dominance of an invasive grass species (U. brizantha), which is also associated with the open canopy conditions.…”

Forests, atmospheric water and an uncertain future: the new biology of the global water cycle

“…One recent review notes that while most studies continue to report reduced runoff, these results provide an incomplete picture as infiltration, rainfall, intermediate-stemdensities and scale-effects are generally neglected (Filoso et al 2017). They also highlight that while local water yields often decline under young regrowth forests, yields change and may recover as the vegetation matures, though this trend is beyond most short-term studies (Filoso et al 2017).…”

Landscapes, at your service: applications of the Restoration Opportunities Optimization Tool (ROOT)

“…One common example is the trade-off among restoration for increased carbon stocks and for increased water yield. As carbon stocks increase (through forest restoration, for example) the available water is often used by growing forests, sometimes leading to lower water yields (Filoso et al, 2017), (although the relationships between restoration and hydrology are far from clear (see Lamb, 2018)). Many current ecosystem services modelling approaches attempt to demonstrate these trade-offs by comparison, whereby each service (carbon and water yield) is visually compared to each other service.…”