The role of dispersal in the management and restoration of fragmented aquatic habitats in agricultural landscapes

The efficient management of water resources is a critical issue throughout Australia.  Plants play an important role in the management of water resources through their role in improving water quality, reducing erosion and providing habitat and food for fish, waterfowl and other aquatic animals.

Seeds and vegetative parts of many aquatic species are dispersed by water

Over the last 200 years, the health of plants in Australia's wetlands and rivers has declined as a consequence of catchment clearing, altered water regimes, salinity, nutrient enrichment and weeds. This has resulted in decreased water quality and less reliable water flows.

These threats are now being tackled and revegetation programs are taking place across Australia. The effectiveness of these restorations activities will be greatly enhanced by improving our understanding of natural processes that contribute to plant biodiversity, such as plant dispersal.

Kay sampling propagules using the water traps

The dispersal of seeds and vegetative parts of plants (collectively referred to as propagules) provide a mechanism by which plants can move across the landscape and arrive at new sites. Propagules of wetland plants and animals move around via wind, water and waterbirds, and also through human activities (eg on boats and car tyres) and via other animals (eg fish and ants). When propagules arrive at a new site and the conditions are right for germination and growth, new plants will establish.

The common reed (Phragmites australis) is dispersed primarily by wind

Our project is unique in that we are assessing how seeds and vegetative parts of plants move between aquatic habitats through wind, water and waterbirds, and how we can apply this knowledge to assist the natural revegetation of rivers and wetlands. For example, during prolonged droughts, wetland plants that can not survive long periods without water will disappear from wetlands. When wetlands re-flood, the movement of seed by wind, water or waterbirds may bring these plants back. Dispersal of propagules may also result in the arrival of new species or new genotypes that have greater tolerance to the local conditions.

The information generated by this project will help habitat managers understand how to best restore and manage aquatic habitats. If we know that propagules of a certain species are arriving in a wetland but we do not see them growing in the vegetation, we may not need to plant those species, but focus on improving the conditions for germination (eg reducing salinity). Alternatively, once a plant species is lost from a site it may no longer arrive of its own accord, and these species may need to be planted. The information generated from this project may also help us contain the spread of weeds in agricultural areas by understanding how weeds move between areas.

The knowledge generated by this project will also enable managers to better protect and restore dispersal pathways that promote natural regeneration. This will provide a mechanism for local plant populations that may have died as a result of disturbances such as flooding, drought or salinity, to re-establish.

Different types of traps are being tested for their ability to capture wind-dispersed seed

Water traps capture propagules floating down rivers

The key outputs of our project are:

• A database of native aquatic plant species occurring in wetlands in Gippsland.
• Improved knowledge of the season, duration and mode of native propagule dispersal (wind, water, waterbirds) for a range of aquatic taxa.
• Determination of environmental flows that maximise dispersal and establishment of native propagules.
• Identification of patterns of dispersal across the Gippsland landscape for key species using genetic tools.
• Improved capacity of natural resource managers, industry and the local community to manage Gippslands aquatic resources at a landscape scale.

Species such as the weed Hawthorn (Cratagus monogyna) can be dispersed by multiple pathways such as water...

...and birds