Temporal Persistence In Northern Jarrah Forest Communities

Quantification of the degree of temporal variability in aquatic fauna communities is important for monitoring and predicting ecosystem responses.

It is especially relevant for the management and monitoring of freshwater streams in the northern jarrah forest of southwestern Australia, which are typically characterised by seasonal and annual extremes of flow.

Collated survey data that span 27 years were analysed to assess constancy (persistence) of aquatic macroinvertebrate species assemblages in upland streams of the northern jarrah forest. Data were derived from replicated, quantitative samples collected seasonally (spring & summer) from four creeks, sampled initially in the mid-1980s and again in the mid- to late-2000s by WRM. Pairwise percentage similarity, which provides a measure of statistical ‘distance’, was used for time series analysis of the overall change in spring (Sept./Oct.) faunal assemblages, relative to baseline condition when first sampled.

Analyses indicated a shift in macroinvertebrate species assemblages away from the baseline condition, by between 10% and 25%. The shift was driven by small changes in abundance of a large number of less common species, including species sensitive to environmental disturbance. The change in community structure reflects a change in flow permanence at these sites, reflecting an approximate 18% decline in rainfall for the area since 1975.