Does forest restoration influence soil infiltrability? A case study in the restored woodland of Sierra de Ávila (Central Spain)

Abstract

Infiltration, as a major component of the hydrological cycle, plays an important role in ecosystems, river flooding, and soil erosion. Therefore, this process has been studied on different soils, with different vegetation cover, and under different climate conditions. However, it is still necessary to know how infiltration rates depend on land degradation, vegetation cover, forest management, and forest restoration, since soil infiltration is related to soil hydrological function and hydrological ecosystem services. The aim of our study is to analyze the way reforestation and check dam construction have helped to improve soil infiltration rates in comparison with old, degraded land, different soils and vegetation covers in Central Spain. Therefore, three infiltration tests were carried out by means of a simple methacrylate infiltrometer ring, in four sampling plots, for five types of land use: (i) native holm oak forest, (ii) 60-year-old reforested pine wood, (iii) shrubs, (iv) sediment wedges of check dams, and (v) gullies and degraded hillslopes. Our results show much higher infiltration rates in the soil of 60-year-old pine reforestation sites (1198.00 mm·h−1), and in the sediment wedges of check dams (1088.00 mm·h−1), than in those of degraded hillslopes (365.00 mm·h−1) and shrubland (420.80 mm·h−1). The rates were also shown to be close to those from the remaining patches of native holm oak woodland (770.40 mm·h−1). We also found that organic matter, humus and litter depth, and height of vegetation and cover, all improve soil infiltration rates, while slope degree, presence of coarse elements, stoniness, clay content, bulk density, and electric conductivity inhibit the rates. It was additionally seen that pine reforestation and check dam construction caused degraded land to recover its hydrological conditions to a level that is quite close to that of the ancient oak holm native forest, alongside ameliorating the hydrological cycle in the watershed. This information will be very useful for decision-making processes related to land restoration projects, forest management, and environmental policy.