Changes in soil physical properties after conversion of tropical montane cloud forest to pasture in northern Costa Rica
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Abstracto
Within the framework of a larger project studying the hydrological impacts of converting tropical montane cloud forest to pasture in the Tilarán range of northern Costa Rica, physical and hydraulic properties of various volcanic soils were compared in two small watersheds covered with mature lower montane cloud forest and pasture, respectively. In situ and laboratory experiments were conducted to determine trends in soil texture, bulk density, porosity, water retention characteristics, infiltration, and (un)saturated hydraulic conductivities with depth under the two types of land cover. Despite their predominantly sandy texture, the soils were rich in organic matter and non-crystalline material such as allophane. Bulk densities were very low and similar between sites for corresponding soil horizons, except for the pasture top-soil which was more compacted, particularly on cow trails. Soil porosity was very high throughout the profile and dominated by macro- and mesopores, again with the exception of the pasture top-soil and the cow trails. Water retention at a suction of 1500 kPa (permanent wilting point) was very high, except in gravelly C-horizons which had low retention capacity. Amounts of plant-available water (i.e. held at suctions between 10 and 1500 kPa) were also high. Surface infiltration rates were relatively high and dominated by “bypass” flow via macropores in the gravelly horizon (at 20–30 cm depth). Spatial variability in infiltration rates was high in the pasture but less in the forest. Saturated hydraulic conductivity at the soil surface was high in general but considerably reduced in the pasture. […].
