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The effects of a thinning treatment on soil respiration (Rs) were analysed in two dryland forest types with a Mediterranean climate in east Spain: a dry subhumid holm oak forest (Quercus ilex subsp. ballota) in La Hunde; a semiarid postfire regenerated Aleppo pine (Pinus halepensis) forest in Sierra Calderona. Two twin plots were established at each site: one was thinned and the other was the control. Rs, soil humidity and temperature were measured regularly in the field at nine points per plot distributed into three blocks along the slope for 3 years at HU and for 2 years at CA after forest treatment. Soil heterotrophic activity was measured in laboratory on soil samples obtained bimonthly from December 2012 to June 2013 at the HU site. Seasonal Rs distribution gave low values in winter, began to increase in spring before lowering as soil dried in summer. This scenario indicates that with a semiarid climate, soil respiration is controlled by both soil humidity and soil temperature. Throughout the study period, the mean Rs value in the HU C plot was 13% higher than at HU T, and was 26% higher at CA C than the corresponding CA T plot value, being the differences significantly higher in control plots during active growing periods. Soil microclimatic variables explain the biggest proportion of variability for Rs: soil temperature explained 24.1% of total variability for Rs in the dry subhumid forest; soil humidity accounted for 24.6% of total variability for Rs in the semiarid forest. As Mediterranean climates are characterised by wide interannual variability, Rs showed considerable variability over the years, which can mask the effect caused by thinning treatment. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Three techniques for obtaining soil water solutions (gravitational and matrical waters extracted using both in situ tension lysimeters and in vitro pressure chambers) and their later chemical analysis were performed in order to know the evolution of the soil-solution composition when water moves down through the soil, from the Ah soil horizon to the BwC- or C-horizons of forest soils located in western Spain. Additionally, ion concentrations and water volumes of input waters to soil (canopy washout) and exported waters (drainage solutions from C-horizons) were determined to establish the net balance of solutes in order to determine the rates of leaching or retention of ions. A generalized process of sorption or retention of most components (even Cl-) was observed, from the soil surface to the C-horizon, in both gravitational and matrical waters, with H4SiO4, Mn2+, Na+, and SO42- being the net exported components from the soil through the groundwater. These results enhance the role of the recycling effect in these forest soils. The net percentages of elements retained in these forest soils, considering the inputs and the outputs balance, were 68% K+, 85% Ca2+, 58% Mg2+, 7% Al3+, 5% Fe3+, 34% Zn2+, 57% CI-, and 20% NO3-, and about 75% of dissolved organic carbon was mineralized. [ABSTRACT FROM AUTHOR]