Tropical stream communities are increasingly threatened by a vast array of human perturbations. However, ecological impacts of deforestation on stream communities are poorly understood in tropical rain forests of Southeast Asia. We investigated the impacts of past riparian deforestation associated with slash-and-burn agriculture on stream habitats and communities in Borneo, East Malaysia, by comparing streams running through primary forests and those through secondary forests that had been deforested 9-20 yr previously. Distinctive differences were found in depositional character of stream habitats; secondary-forest reaches had finer substrates, more eroded banks, and larger areas of depositional habitat and cover than did primary-forest reaches. Although our findings suggest that such altered habitats are recovering toward a predisturbance state with redevelopment of the secondary forests, effects of the habitat alteration on stream communities were still evident. The habitat alteration (i.e., sedimentation) lowered the abundance and/or diversity of every benthic assemblage (periphyton, aquatic insects, shrimps, crabs, and benthic fishes), while nektonic fishes were less affected. Although the habitat alteration benefited a few benthic taxa, such as caenid mayflies and two shrimps (Macrobrachium trompii and Caridina nilotica peninsularis), the overall effects were apparently detrimental, leading to a reduction in biodiversity of the stream communities. We concluded that slash-and-burn agriculture, which alters vegetation and soil conditions more intensively than logging, caused long-term degradation of stream communities (at least nine years in our study). These findings emphasize the importance of management practices that protect the stream biodiversity from poorly regulated land use in Southeast Asia.
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