Changes in stream biota along a gradient of logging disturbance, 15 years after logging at Ben Nevis, Tasmania

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We compared the instream biota of five first-order granitic headwater streams and five similar streams which had experienced a range of intensity of clearfell operations 15 years previously. We observed substantial differences in benthic macroinvertebrate community composition and abundance, aquatic insect emergence rates and abundance of macrophytes and algae between the two stream groups. Differences in the riparian vegetation structure, stream channel form and habitats and sediment composition of these streams had previously been ascribed to the effects of the clearfell operations and related to the intensity of historical forestry-induced disturbance. Instream biological responses (changes in macroinvertebrate assemblage composition and declines in abundance) were correlated with both a measure of the intensity of the degree of historical clearfell disturbance and with the amount of fine particulate organic matter (FPOM) in the stream substrate. Differences in macroinvertebrate abundance between channel and pool habitats were also associated with inter-habitat differences in substrate FPOM loading. We suggest that the magnitude of the response of benthic fauna along the disturbance gradient is mediated by the effect of disturbance on the storage of FPOM, which is both a habitat and food source, and that the clearfelling has induced long-lasting deficits of bioavailable organic carbon stores and backwater habitats in these streams.