No abstract

Abstract:Plant communities and ecosystem processes in seres at multiple altitudes in the tropical montane forest zone of northern Borneo were studied to understand the patterns and mechanisms of the secondary succession after shifting cultivation. A total of 25 stands (and additional three stands) were sampled with stand ages ranging from 2 to 55 y after slash and burn at altitudes between 900 and 1400 m asl. Plant species composition, above-ground biomass (AGB), chemical properties of soils, litter and foliar samples were investigated in each stand. A TWINSPAN analysis classified five plant communities primarily as a sere but with two altitudinal communities in the later successional phase. AGB accumulated steadily at the rate of 2.42 Mg ha−1 y−1 during the succession for the first 55 y due to the ontogenetic development of plants as well as plant community shifts. At the onset of secondary succession, pool of soil NO3-N and soil total P was high probably because burning caused flushes of minerals originating from the burnt plant materials. Pool of soil NO3-N and soil total P decreased with increasing stand age during the succession. Leaf-litter N:P ratios of dominant species significantly increased with increasing stand age suggesting disproportionately greater P deficiency than N deficiency in the later successional phase. It is suggested that tree species shifted to those of greater P-use efficiency during succession in response to decreasing soil P availability. We conclude that the interaction of altitude with the reduction of soil N and P availability was related to the altitudinal split of plant communities in the later phase, while pioneer communities were wide-ranging across altitudes reflecting richer soil nutrients.

Tropical countries are now facing increasing global pressure to conserve tropical forests, while having to maintain cultivated lands (particularly shifting cultivation) for the subsistence of local people. To accomplish the effective conservation of tropical forests in harmony with subsistence shifting cultivation, we evaluated the influence of shifting cultivation on ecosystem services (i.e., biodiversity and carbon stock) at a landscape level based on three land-use scenarios. The study focus was the upland area between the Kinabalu Park and the Crocker Range Park in Sabah, northern Borneo, where local people conduct shifting cultivation for their subsistence. In this area, vegetation patches of various stages of secondary succession admix with shifting-cultivation lands. An earlier study in the same site depicted significant relationships between the stand ages of vegetation patches (which form a sere of secondary succession after the abandonment of cultivated land) and the above-ground biomass (i.e., carbon stock) and species composition of the stands. We incorporated these significant relationships to a stand-age estimation algorithm that had been developed earlier. We first mapped current (as of 2010) spatial patterns of the above-ground biomass and plant-community composition for the whole landscape. Subsequently, we simulated the spatiotemporal patterns of the above-ground biomass and plant-community distribution using three land-use scenarios: (1) reducing the area of shifting cultivation by one half and protecting the rest of the area; (2) shortening the minimum fallow period from 7 to 4 years while maintaining the same area of cultivation; and (3) elongating the minimum fallow period from 7 to 10 years while maintaining the same area of cultivation. Results indicated that land use based on scenario 2 could increase the carbon stock while maintaining the cultivation area. Our methods were effective in mapping the structure and composition of highly dynamic forests at a landscape level, and at predicting the future patterns of important ecosystem services based on land-use scenarios.