Replacement of Grasslands With Polylepis Forests Reduces Aquifer Recharge in the Seasonally Dry Andes

Abstract

The High Andes biome—which includes grasslands, peat‐forming wetlands known as bofedales , and native forests—provides vital ecosystem services, such as water regulation, to millions of people living downstream. Although recent studies have highlighted the hydrologic regulation of native grasslands and bofedales , and quantified reductions in water yield resulting from afforestation with exotic species, little is known about changes in water resources resulting from the conversion of native grasslands to Polylepis forests. We measured hydrologic fluxes from the root zone to catchment scale in Jarava Ichu grasslands, a young Polylepis forest (afforested over 0.568 km ² in 2016–2017), and a mature Polylepis forest in the seasonally dry puna of the Cusco region, Perú. Compared to grasslands, the Polylepis root zone experienced more drying, reached field capacity later in the wet‐up, and passed an average of 41% less water annually to the underlying aquifer. Average annual evapotranspiration from young and mature Polylepis was 1.9 and 3.2 times larger than from J. ichu grasslands, respectively. Despite the varied ecosystem services provided by native forests to the local and regional communities, we predict a 10%–11% reduction in aquifer recharge in the Upper Ramuschaka Watershed (2.12 km ² ) if the afforested Polylepis grows to maturity. The results presented here will guide hydrological modeling in the region and inform community‐led discussions assessing the relative importance of the ecosystem services provided by the varied landcovers of the puna biome.