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ABSTRACT Afforestation of formerly open, water‐limited habitats is a globally widespread form of land conversion, driven by the need for timber and non‐timber forest products, and capturing atmospheric carbon. However, increased tree cover can adversely affect hydrological cycles by increasing evapotranspiration and reducing downslope water yield, threatening agricultural production and water‐dependent habitats. Here, we assessed the effect of afforestation with the non‐native Robinia pseudoacacia in dry sandy upland areas of Hungary on the water supply of adjacent wetlands, and experimentally tested whether forest thinning can restore the hydrologic regime. We found that little moisture seeped down to the subsoil of plantations due to increased precipitation interception and transpiration, compared with grassy uplands. The lack of deep infiltration precluded lateral moisture seepage across the upland–wetland ecotone during the growing season. Conversely, we detected no notable interruption of lateral flows from grassy upland areas. Forest thinning (approx. 40% of the basal area) did not meaningfully improve water availability, probably because the effects of lower interception and transpiration were offset by the disruption of the understorey microclimate and the quick recovery of the canopy cover. We conclude that the afforestation of upland areas is an important contributor to wetland loss in the region and partial solutions are of limited effectiveness. We recommend a landscape‐wide reconsideration of forestry strategies on uplands and planning alternative land use types to support soil moisture infiltration. One possible approach is to restore the original open ecosystems, but supporting solar developments in these marginal areas is also a viable option.
Tölgyesi et al. (Mon,) studied this question.