Abstract:
This report describes a survey of riparian vegetation diversity, which was one part of a Synoptic Biodiversity Survey, undertaken by the CRC for Freshwater Ecology in 2001, and funded exclusively by the Sydney Catchment Authority (SCA). The over-arching purpose of the whole synoptic survey was to make a preliminary assessment of the distribution and variability of riparian and in-stream biodiversity across the catchments under the responsibility of the SCA, and to identify sites of scientific significance.
The vegetation survey recorded 383 native plant species, with the number of species per site ranging from 2 to 67. Species of conservation significance were recorded, and these included three rated as ‘Vulnerable’ under Federal legislation, and twelve of regional significance.
A total of 162 alien plant species were recorded, with the number per site ranging from 1 to 43. In-channel plant diversity was not sampled, but the streamside plots showed a high level of macrophyte species diversity, including a large number of emergent macrophytes. The vegetation in one-third of the sites was structurally dominated by alien plant species and these sites also had a high proportion (60%) of alien species in their understorey. Sites with native species as dominants were also highly invaded by alien species (33% alien), indicating the potential of the latter to dominate sites following disturbance.
It was found that even sites in reference areas had alien species present. This highlights an issue currently engaging the research community, of incorporating reference condition in a quantitative form into monitoring designs. Development of a reference condition for riparian vegetation is required. It should be developed as part of comprehensive vegetation/habitat classifications and robust species distribution models to form the baseline for riparian vegetation biodiversity assessment.
Modelling the richness components of biodiversity demonstrated how different components of biodiversity are influenced by specific environmental characteristics at the plot and site level. Models linking single species to the riparian environment will require substantially larger sample sizes and sampling effort, especially if the target species are native. Without this, the species likely to achieve suitably high frequencies are the widespread alien species such as willows and blackberry.
In the absence of standard protocols for identifying sites of scientific significance, an exercise was done using data from this survey. The results showed that special procedures will need to be developed if sites of scientific significance need to be identified.
Plot and site summaries of some of the key data are provided as appendices in this report |