Effects of selective forest harvesting best management practices on organic matter and invertebrate detritivores in streams draining subtropical eucalypt forest

Abstract

Best management practices (BMPs) for forestry activities have been developed to mitigate the impacts of timber harvesting on stream ecosystems in New South Wales, Australia. These BMPs include selective harvesting within the catchment, exclusion of harvesting in riparian zones, and restrictions on harvesting and machinery operations during wet weather or on steep slopes. The few studies assessing the ecological effects of forestry BMPs have largely focussed on operations in temperate climates and are often based on a single pair of control and impact streams. But what are the effects in subtropical regions where climatic and hydrological variability may be greater? Are the effects of selective harvesting dependent on the proximity of harvesting to the locations of monitoring? We used a multiple paired-catchment study to assess effects of forestry BMPs on standing stocks of benthic coarse particulate organic matter (CPOM) and densities of invertebrate detritivores in streams draining subtropical eucalypt catchments that were either harvested using BMPs (‘impact’) or unharvested (‘control’). CPOM and detritivores in three pools in each of the four streams were sampled multiple times before and after the impact catchments were harvested. Harvesting intensity and proximity of harvesting to stream monitoring sites differed between ‘impact’ catchments. Benthic CPOM was dominated by leaves and leaf fragments in all streams. There were no post-harvesting differences in CPOM composition, standing stocks of different CPOM fractions or densities of detritivorous stream invertebrates in two feeding groups (collector-gatherers and shredders) between stream pairs despite differences in the proximity (minimum of ∼50 m and 1.6 km) of harvesting to monitoring sites. We conclude that relative to matched control sites, selective forestry BMPs do not alter CPOM stocks and stream detritivore densities in this subtropical Australian eucalypt forest, implying that these BMPs are effective in mitigating effects of harvesting across similar subtropical forests.