How do Water Regime and Grazing Alter the Reproductive Capacity of Aquatic Plants?

Dr Margaret A. Brock
Botany, Rural Science and Natural Resources, University of New England
Environment Australia, 2000

5. Summary of Project

In the UNE Experimental Wetlands with 5 replicated water regimes, within two years of planting donor seed banks:

A species- rich vegetation has developed in which both sexual and vegetative reproduction have occurred in each water regime.
A species-rich seed bank has developed in the wetlands from reproduction of the establishing community under all water regimes.
Water regimes stimulated different plant communities from planted seed banks, different in space, species composition and in reproduction.
Water regimes sustain different plant communities in the wetlands.
Grazing, assessed by clipping, in interaction with water regime influences plant reproduction: for submerged plants reproduction was reduced, for some amphibious species where water levels changed from flooded to damp clipping increased reproduction and in other species it had no influence.
Water regime did not select for particular species groups but may select for which plants reproduce. Planting donor seed banks in spring in wetlands that are filling allows aquatic species to flower and add seed to the seed bank before winter.

Some generalizations for most wetlands include (see attachment m):

Shallow habitats with amphibious plants change as water levels rise and fall.
Many plant species tolerate or respond quickly to water level changes.
Permanently flooded habitats have submerged plants that don't tolerate drying.
Terrestrial edge habitats tend to have weedy plants which don't tolerate flooding.
A mosaic of habitats provides a diverse set of conditions for wetland biota.
Fast lowering or raising of water levels leaves edge habitats bare of aquatic plants
Steep sided wetlands won't have wide zones of aquatic plants stimulated by water level fluctuations.

Project outcomes that continue to generate data and management outcomes include:

Continued data collection on vegetation establishment and reproduction under different water regimes in the UNE Experimental Wetlands will allow longer term predictions for other systems.
Following the development of a viable seed bank in a set of constructed wetlands over two years since planting a donor seed bank and following this for a further period will allow predictions for wetland rehabilitation.

Project outputs

The production of two booklets with techniques for managing wetland plants and water regime are our major project outputs for management:

"Are there plants in your wetland? Revegetating wetlands" (Brock and Casanova 2000)
"Does your wetland flood and dry? Water regime and wetland plants". (Brock, Casanova and Berridge) due for publication September 2000).

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