This study highlights soil fertility status as well as plant structural and compositional makeup in two different forest types after being exposed to different levels of anthropogenic disturbances. The mineral soil chemical analysis (pH, conductance, percentage of carbon and nitrogen, Cation Exchange Capacity (CEC), potassium, sodium, magnesium, calcium, and total and available phosphorus) showed that the concentrations of the chemical elements were lower than the values of published results from other studies in Borneo, suggesting a serious habitat degradation due to prior land-use in the forest reserve. In terms of plant abundance and richness, the logged-over forest fragments were dominated by small trees, whereas the understorey of tree plantations was composed of dense ferns and sedges with very low tree abundance and species richness. This study therefore provides important information on the management of soils and plant diversity in the tropics.

In the tropics, primary forests are routinely converted into a variety of land-use types such as plantations of monocrops, farms and shifting cultivation, and this practice has led to soil degradation and low biodiversity (Laurance et al., 1998; De Jong et al., 2001; Cochraneet al., 2002; and Hashim, 2006). Plant species in these degraded sites may be very different from their original habitats as a direct consequence of forest clearing and harvesting activities or when the underlying soils, light environment and hydrological processes are also disturbed. In addition, forest harvesting may also significantly change abiotic properties of forest habitats; for example, soil nutrient reserves are often reduced by logging activities (Nykvist, 1998).

Patterns of anthropogenic disturbance in an area may not be very simple, however, logging, followed by shifting cultivation, is one of the most common land-use syndromes in the tropics (Lim and Hamzah, 1985; and McKinnon and Sumardja, 1996). When logged-over forests are cleared for agriculture, some fragments could be left intact. Consequently, logged-over forest fragments suffer from both habitat degradation because forest harvesting reduces the soil nutrient reserves from habitat fragmentation. In comparison, shifting cultivation farms experience severe habitat degradation from forest clearing, burning, soil erosion and nutrient leaching, because the slash from forest clearing is burned for easy planting process and weed suppression and to release some nutrients into the soil. The burned ash is actually devoid of nitrogen and sulphur, whilst other nutrients may be lost via rainwater runoff (Lee, 1981; Hatch, 1982; and Sim and Nykvist, 1990). After abandonment, the farms are covered mostly by weedy plants such as the lalang grass (Imperata cylindrica) and the resam fern (Dicranopteris linearis) that are adapted to open and nutrient-poor areas, and these hardy species can persist on the sites and act to arrest the regeneration of later successional species (Nykvist, 1996; and Lee et al., 2002).

In Borneo, rehabilitation projects are commonly carried out to increase soil fertility, vegetation biomass and diversity in the degraded habitats of former shifting cultivation and logged-over forests (Lim and Hamzah, 1985; and Sarawak Forest Department, 2008). The objective of this study is therefore to describe the soil properties in degraded forests following different disturbance and rehabilitation regimes. In relation to the soil properties, the structure and composition of plant species in the forests were also assessed.

Soil And Water Sciences Journal, Soil Fertility, Weed Suppression, Soil Degradation, Soil Erosion, Planting Process, Mixed Dipterocarp Forests, Timber Species, Plantation Species, Mineral Soil Nitrogen, Cation Exchange Capacity, Plantation Plots.