Benchmarking Riparian Vegetation Quality in Recovering Rivers: Implications for Management of Novel Ecosystems.

Abstract

Anthropogenic disturbance has led to widespread vegetation clearing and geomorphic adjustment along most of the world's rivers. Over the past 50 years, riparian vegetation has been returning, unassisted, to rivers in eastern Australia that have been experiencing geomorphic river recovery. We used a novel rapid riparian assessment method to analyse vegetation condition on rivers undergoing geomorphic recovery. The rapid riparian assessment method incorporated vegetation cover, native species richness, the proportion of native to exotic species cover, and other features of vegetation health to produce a vegetation condition score that classifies sites as poor, moderate, or good. Vegetation condition was analysed along 36 river reaches in coastal catchments of New South Wales (NSW) in three different climatic regions (North, Mid and South coasts), covering three stages of geomorphic recovery (low, moderate and high) and for three geomorphic units (bars, benches and floodplains). Most reaches had a poor or moderate riparian vegetation condition, with only three sites assessed as being in good condition. Native species richness and proportion of native to exotic species cover were higher in the later stages of geomorphic recovery and on benches and floodplains, compared to bars. However, most of the riparian vegetation on recovering rivers consisted of a mixture of native and exotic species, highlighting that even in the later stages of recovery, novel communities are produced that do not resemble the pre-disturbance ecosystem. To improve vegetation quality at-scale (i.e. across catchments and regions) will require that vegetation management interventions are designed and adapted to work with these novel ecosystems, and that realistic rehabilitation targets and expectations are set to account for the geomorphic and vegetative recovery that is occurring along these rivers.