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.