Effects of afforestation on water yield: a global synthesis with implications for policy

Abstract

Carbon sequestration programs, including afforestation and reforestation, are gaining attention globally and will alter many ecosystem processes, including water yield. Some previous analyses have addressed deforestation and water yield, while the effects of afforestation on water yield have been considered for some regions. However, to our knowledge no systematic global analysis of the effects of afforestation on water yield has been undertaken. To assess and predict these effects globally, we analyzed 26 catchment data sets with 504 observations, including annual runoff and low flow. We examined changes in the context of several variables, including original vegetation type, plantation species, plantation age, and mean annual precipitation (MAP). All of these variables should be useful for understanding and modeling the effects of afforestation on water yield. We found that annual runoff was reduced on average by 44% ( AE 3%) and 31% ( AE 2%) when grasslands and shrublands were afforested, respectively. Eucalypts had a larger impact than other tree species in afforested grasslands (P 5 0.002), reducing runoff (90) by 75% ( AE 10%), compared with a 40% ( AE 3%) average decrease with pines. Runoff losses increased significantly with plantation age for at least 20 years after planting, whether expressed as absolute changes (mm) or as a proportion of predicted runoff (%) (Po0.001). For grasslands, absolute reductions in annual runoff were greatest at wetter sites, but proportional reductions were significantly larger in drier sites (Po0.01 and Po0.001, respectively). Afforestation effects on low flow were similar to those on total annual flow, but proportional reductions were even larger for low flow (Po0.001). These results clearly demonstrate that reductions in runoff can be expected following afforestation of grasslands and shrublands and may be most severe in drier regions. Our results suggest that, in a region where natural runoff is less than 10% of MAP, afforestation should result in a complete loss of runoff; where natural runoff is 30% of precipitation, it will likely be cut by half or more when trees are planted. The possibility that afforestation could cause or intensify water shortages in many locations is a tradeoff that should be explicitly addressed in carbon sequestration programs.

Determining the hydrological responses to climate variability and land use/cover change in the Loess Plateau with the Budyko framework

“…For the Tou-Tong catchment, the amounts of vegetation coverage in 1978, 1998 and 2010 were 33.73%, 35.52% and 46.91%, respectively. Vegetation restoration is considered to be one of the most effective measures in reducing streamflow and minimizing erosion (Farley et al, 2005). As shown in Fig.…”

Effects of Forest Cover Change on Flood Characteristics in the Upper Citarum Watershed

“…Generally, these researches (Hibbert 1967;Bosch & Hewlett 1982;Andre´assian 2004;Brown et al 2005) use paired catchment experiments approach. The general conclusion indicate that forest cover reduction (deforestation) will increase water yield, whereas reforestation in opened land will decrease it (Bosch & Hewlett 1982;Andre´assian 2004;Farley et al 2005;Lima et al 2012). The amount of this reduction varies from one experiment to another (Bruijnzeel 2004), and this is caused by a complex interaction among vegetation, climate, and soil (Zhou et al 2010).…”

Mycorrhizal Interactions for Reforestation: Constraints to Dryland Agroforest in Brazil

“…In general, C sequestration strategies highlight tree plantations without considering their full environmental consequences, such as losses in stream flow, and increased soil salinization and acidification, with afforestation of monocultures, for example, in the USA. Therefore, 2 ISRN Ecology monocultures that maximize carbon sequestration can have considerable impact on runoff and groundwater recharge [11], including reduced stream flow [12] and decreased soil pH and base saturation. Reforestation of floodplains can also be beneficial for maintaining biodiversity, reducing erosion, improving water quality, mitigating peak flows, and controlling groundwater discharge (upwelling) [11].…”