WEED ECOLOGY - Other Weeds
Salvinia invasion and biocontrol in regard to conservation of biodiversity and ecosystem management
Researchers: Bertie Hennecke and Kris French
Salvinia molesta
The aquatic fern Salvinia molesta D.S. Mitchell continues to be one of the most prolific invaders of freshwater systems in Australia and control methods in temperate regions particularly have been inconsistent and ineffective. Moreover the effects of Salvinia invasion and control methods on the ecosystem are not understood especially in terms of plant species biodiversity.
Infested creek in the Hawkesbury Nepean River system
A case study system, the Hawkesbury-Nepean River , was utilised to investigate two aspects of salvinia invasion and control:
1. conservation; to improve the understanding of effect of salvinia invasion and the effect of current control efforts,
2. management; to investigate augmentative releases of biological control as a new method tailored to temperate regions.
Investigating competition between native aquatic plants and salvinia.
Our plant diversity assessment carried out across the Hawkesbury-Nepean River system revealed that a large number of native plant species have been lost due to disturbance and subsequent invasion of a few dominant exotic plant species, such salvinia, alligator weed ( Alternanthera philoxeroides ) and dense waterweed ( Egeria densa ). This replacement of native species with exotic species was especially predominant in nutrient enriched habitats. Furthermore, we discovered low population densities of most other native species implying these species are at risk of extinction.
Applied management strategies e.g. biocontrol or harvesting fell short of reducing the impact and threat of this invasive species to biodiversity and therefore failed to contribute to ecosystem management as salvinia was replaced by one of other significant invaders, dense waterweed.
We investigated augmentative biocontrol trials at low temperature developmental thresholds of the agent Cyrtobagous salviniae and showed that this technique applied at optimum timing has the potential to enhance the efficacy of biocontrol of salvinia in temperate regions and can therefore expedite biocontrol at the onset of the salvinia growing season to reduce the invaders impact across ecosystems. However, our work so far highlighted that conservation of biodiversity and maximisation of functions of aquatic system in disturbed environments requires ecosystems management on a broader level rather than targeting only one single invasive species. Therefore any effective control method of individual invasive species needs to be considered within a broader ecosystem management plan.
Experiment to investigate microbial activity
and water quality in invaded areas
|
