Response of wetland plant communities to inundation within floodplain landscapes

Abstract

This paper arose from a need to determine if wetlands that have been dry for many years or even decades, would respond to artificial inundation and provide a basis for developing an environmental water management plan within the Murray Valley. Summary Many floodplain wetlands in south-eastern Australia have become isolated from the main river channel as a consequence of reduced high flows and associated flood events following river regulation. In the Central Murray region of south-eastern Australia, many temporary wetlands would have received water once every five years or so, with large floods maintaining floodplain connectivity every decade, under natural conditions. Now, the River Murray is highly regulated and many of these wetland areas have not been flooded for periods of up to 30 years. Consequently, these wetlands are becoming degraded and the biodiversity of the area is in decline. From 2001From -2003 Black Box depression wetlands in the Central Murray region were each watered once. Plant communities in each wetland were monitored for changes in abundance (assessed as percentage cover) before and during the wetting and drying phases. Wetlands were watered during spring or early summer with the length of inundation ranging from 6 to 19 weeks. After watering, the percentage cover of native plant taxa and native plant functional groups in most wetlands increased. In general, there was a decrease in the percentage number of terrestrial plants present and an increase in the percentage cover of aquatic plants. Introduced species were a minor component. Although these wetlands are all located in the Central Murray region, individual wetlands developed plant communities that contained taxa specific to individual wetlands despite initial similarities. These results indicate that wetland plant biodiversity within the landscape can be promoted and maintained by ensuring there is a diversity of wetlands with varying flood regimes within the landscape.

The value of plant functional groups in demonstrating and communicating vegetation responses to environmental flows

“…The results of our vegetation surveys were consistent with those of others who have previously demonstrated that plant species composition at individual wetlands is often highly site‐specific, with very few species common across a large number of wetlands (Brock et al ., ; Alexander et al ., ; Barrett et al ., ). We found that this was also true of genera, which were often particular to wetlands, and to a lesser extent families.…”

“…While there were still significant differences in the plant species assemblages recorded between inundation classifications, the similarity of plant species communities between individual wetlands within inundation classifications was relatively low. This supports previous findings that, at the species level, plant community responses to watering regimes often vary significantly between individual wetlands (Alexander et al ., ; Barrett et al ., ). By reducing the number of response variables used in the current study (in this case from 270 species to 10 WPFGs), the similarity of communities between wetlands within each inundation classification greatly increased and the significant differences between individual wetlands were removed.…”

“…Demonstrating and predicting wetland vegetation responses to different watering regimes can be difficult in intermittent floodplain wetlands. Plant communities in these habitats can exhibit extensive spatial and temporal variability in species composition and abundance (Boulton & Brock, ; Alexander, Nielsen & Nias, ; Barrett, Nielsen & Croome, ). This inherent variability may reduce the confidence water managers have in predicting the plant communities likely to result from prescribed watering regimes.…”

Mapping inundation in the heterogeneous floodplain wetlands of the Macquarie Marshes, using Landsat Thematic Mapper

“…The role of the flooding regime, extent, frequency and duration, is also critical for dependent organisms, including vegetation (Alexander et al, 2008;Casanova and Brock, 2000;Roberts et al, 2000), micro-invertebrate density (Jenkins and Boulton, 2003), fish movement and spawning (King et al, 2009), and waterbird abundances at the landscape scale. However defining the flooding thresholds which trigger ecological responses of interest is difficult in complex systems, especially regulated systems where there are competing demands for water (Acreman and Dunbar, 2004).…”

Water quality, nutrient, phytoplankton and microcrustacean responses to watering of private wetlands in the Murray Valley, New South Wales

“…Benefits to vegetation and higher trophic groups following inundation have been documented (Nias et al. 2003; Alexander et al. 2008), yet water quality, nutrient and lower trophic level responses remain unsolved.…”