Tree invasion of an intermittent wetland in relation to changes in the flooding frequency of the River Murray, Australia

Abstract

Aerial photographs taken in 1945Aerial photographs taken in , 1957Aerial photographs taken in ., 1970Aerial photographs taken in , and 1985 were used to examine the invasion of red gum {Eucalyptus camaldulensis Dehn.) into an extensive, natural grassland. This grassland occupied a high flood frequency stte adjacent to the major River Murray, Australia. Photogrammetric techniques were used to provide information on the successive states of 200 m X 200 m grid cells covering the wetland. The information collected was then assembled into a Markov Chain model of change in the wetland. Prior to 1945 the tree-plain boundary appears to have been stable. The model, extrapolated into the future, showed the almost complete extinction of extensive grass plains, although small-scale intimate mixtures of plain and red gum will exist as a stable form. Analysis of hydroperiods suggested that a major factor in this is the increased summertime levels and reduced winter-spring levels of the River Murray as a consequence of the need for downstream transmission of irrigation water. The affected areas tend to lie between the summertime heights of the river in the pre-regulation and post-regulation days. Although there are few water management options for this particular wetland, it is likely that other riverine wetlands have suffered similar changes but could be managed to avoid some of the adverse effects of such changes in hydroperiodicity.

Decline of an endangered amphibian during an extreme climatic event

“…3C). In wetland environments tree invasion occurs as a result of increased dryness (Bren 1992, Berg et al 2009), indicating that extinction sites have experienced prolonged periods of desiccation. At the pool and nest level there were no significant relationships between habitat variables measured at randomly selected pool and randomly selected nest locations at the three different site types, with the exception of presence of water (Fig.…”

Climate-change threats to native fish in degraded rivers and floodplains of the Murray–Darling Basin, Australia

“…Anecdotal evidence, for instance, suggests that common reed was historically more widespread in terminal floodplains of the MDB and the decline in the extent of this species may reflect reductions in flood frequency, as well as grazing pressure, in such areas (Roberts 2001). Moira grass plains on floodplains of the Murray River are also threatened as a result of waterresources development, both as a direct result of changes in flood frequency, duration and timing on the life history of this species, as well as indirectly as a result of their encroachment by both river red gum and giant rush because of altered flooding patterns (Bren 1992;Roberts 2001).…”

Effects of hydrologic modifications to riparian plant communities in a large river system in northern China

“…Respective percentages of mesics and xerics increased, while hydrics decreased dramatically. Replacement of hydric species by more mesic species has been recorded in studies of floodplains subjected to flow regulation (Bren 1992;Kingsford and Thomas 1995). Two divergent responses to flow regime change in two stages of hydrologic modification indicates that the structure of the plant moisture group had a certain tolerance to water availability loss.…”