THE IMPACT OF MANAGEMENT PRACTICES OF EXOTIC WILLOWS (SALIX SPP.) ON AQUATIC INVERTEBRATE COMMUNITIES IN SOUTH AUSTRALIAN FRESHWATER STREAMS

Abstract

The impact of willows, their removal and subsequent revegetation on aquatic invertebrate communities were examined in two freshwater streams in the Mount Lofty Ranges, SouthAustralia. We hypothesized that lower abundance, species diversity and changes in functional feeding groups would occur where willows were present and have been removed. Unexpectedly, invertebrate abundance was significantly higher when willows were present in both streams. The introduced hydrobiid snail (Potamopyrgus antipodarum) was the most dominant taxon overall and was significantly more abundant under willows in both streams. More than half of total abundance under willows was contributed by scrapers (mostlyP. antipodarum) as willow roots are presumed to provide a more stable habitat from high currents and have increased food availability compared with other vegetation. Where willows were removed and not revegetated, there were lower invertebrate species numbers and diversity in both streams. The removal of willows influenced not only loss of habitat, but also an increase in light intensity, decline in water quality and food availability. Our findings conclude that the presence of willows also reduces species numbers and diversity. Large scale willows removal may need special management considerations in order to reduce the impact on aquatic invertebrate communities.