Authors: Tölgyesi, Csaba; Hábenczyus, Alida Anna;Török, Péter;Bátori, Zoltán;Tóth, Benedek;Valkó, Orsolya;Deák, Balázs;Kelemen, András;

Tree planting campaigns are spreading globally to mitigate climate change by sequestering carbon. Afforestation, however, can have adverse effects in formerly open landscapes, including the loss of native biodiversity and water shortage. Here we assessed the strength of the trade-off between tree cover and water loss on contrasting soil types in temperate semiarid regions. With an intensive, year-round monitoring of soil moisture, we found that forests on sand retain topsoil moisture throughout the year but below this a thick dry layer develops during the vegetation period, which gets filled up to field capacity only in the winter, hindering groundwater recharge. Grasslands on the other hand have drier topsoil throughout the vegetation period due to direct insolation but the moisture reserves below are not affected and allow deep percolation. In contrast, deep soil desiccation has not been encountered in the forests of cohesive soils. Topsoil heavily dries out in the grasslands of cohesive soil, so the water balance seems to be more negative in them. We conclude that in flat semi-arid areas, where landscape-wide water regime depends on deep percolation, sandy soils should be avoided for afforestation, while the trade-off between water and carbon is not so severe on cohesive soils.