Clearing of stream catchments for agricultural development exposes invertebrate communities to chronic adverse environmental and physical conditions over long periods, including sediment transported in from landscape runoff, higher temperatures, and a shortage of allochthonous organic material for food and habitat. These effects can be exacerbated by short-term changes in flow, which carry invertebrates and organic material downstream and collapse streambanks, burying remaining food sources and altering benthic habitats. Response traits, their distributions and their diversity in affected streams have been used to predict how invertebrates cope with short-term stressors, but interactions with larger-scale, longer-term disturbances remain poorly understood.
To explore whether and how flow-related traits respond differently in different levels of catchment clearing to short term flow manipulation we conducted a multiple control-impact and recovery (mCIR) experiment in southwestern Australian streams. The region has seen 70 years of extensive land clearing and 50 years of climate drying. Temporary half-weirs were constructed in eight streams, 4 with < and 4 with > 30% catchment clearing. Weirs altered flow, creating fast and slow patches. Invertebrates were sampled at two and three weeks after weir construction and at one and two months after weir removal from the two altered flow reaches, and from a control reach upstream. Flow related traits were attributed using existing trait databases.
Some patterns in trait distributions among flow treatments were detected, mediated by level of catchment clearing, however, these patterns were temporally complex (indicating some delayed responses to flow disturbance), and were obscured by differences among streams. Where streams have distinct communities with distinct sets of traits, they will show distinct responses to both long- and short-term disturbance. Thus, caution must be exercised when interpreting trait responses to disturbance in landscapes where species turnover (β-diversity) is high.