| The objective of this study was to characterize the spatial pattern, frequency, predictability and severity of disturbances generated by anthropogenic activities and compare them to other gap-forming disturbances in a tropical rainforest. The effects of disturbances were assessed in terms of plant community composition and structure, successional dynamics and vegetation heterogeneity. Shifting cultivation practices of the Kenyah Dayak were used as a case study in the Apo Kayan, a remote upland plateau in East Kalimantan, Indonesia. Data collection included mapping agricultural fields, plot and line-intercept sampling, surveys of household labor and rice production, and open-ended interviews.; Results showed this anthropogenic disturbance generates clusters of patches up to 30 ha consisting of rice fields and successional vegetation. The size of fields, their location and the age of fallow vegetation cut varied and were determined partially by household circumstances. Forest canopy cover rapidly returned during plant succession in fallow fields. In one secondary forest, coppicing trees dominated and accounted for 25% of total basal area. A site cultivated for many consecutive years contained few forest species and was dominated by pantropical weeds. The most severe disturbance was from erosional landslides, although shifting cultivation affected more area per year. Alternatively, the concentration of agriculture to certain locations allowed large tracts of primary forest to remain uncut.; These results demonstrate the difficulty of assessing disturbance impact based on a single variable such as frequency or average size of gap. Further, the variability of land uses and factors affecting agricultural decision-making need to be carefully documented in order to accurately extrapolate previous patterns of anthropogenic disturbances and to anticipate future changes.; Long-fallow shifting cultivation may generate secondary forests containing trees able to recolonize fields more rapidly than forest only recently felled for agriculture and may also result in greater spatial and resource heterogeneity at the landscape scale. |
