Effects of progressive catchment harvesting on stream invertebrates in two contrasting regions of New Zealand's North Island

Abstract

We examined changes in stream habitat and benthic invertebrate communities in two contrasting regions of New Zealand’s North Island over a 9–10-year period as pine forest harvesting progressed through the catchments. Increases in streambed cover by sand/silt, wood and macrophytes were recorded as harvesting progressed, but little change was observed in qualitative periphyton abundance. Despite similar high-level taxonomic structure of invertebrate communities between the two regions, differences in percentage and log-transformed abundance indicated an effect of landscape context that reflected different hydrologies and bed-substratum stabilities. Within regions, ordination plots indicated broadly distinct site clusters that persisted through time and reflected variations in stream size, substratum composition, periphyton abundance and degree of catchment harvesting. Generally, few of the invertebrate community metrics examined showed clear responses to progressive catchment or onsite harvesting relative to previous intra- and inter-annual variation. The most noticeable exceptions were percentage Ephemeroptera, Plecoptera and Trichoptera (excluding Hydroptilidae) abundance and percentage Elmidae abundance, which were negatively and positively correlated, respectively, with percentage catchment harvested. We identify three broad response categories to catchment harvesting that reflect subsidy–stress effects as logging progressed and discuss the relevance of these findings to potential pine forest harvesting effects in southern Australia.