The climate of the south-west region of WA is drying rapidly. Already many wetlands and streams no longer contain water at any time. Many other wetlands and streams have changed from perennial (containing water year round) to seasonal (containing water only in winter and spring). Water regime (the volume and timing of water) is the most important determinant of stream and wetland biodiversity. Many freshwater plants and animals rely on perennial water, yet that is becoming scarce in our landscape. In the Perth Hills, most streams that are not in water catchments have been dammed for farm water supply. These small dams may provide perennial water in a landscape where perennial water is otherwise scarce, yet we know nothing about whether these dams can provide habitat for native plants and animals. In dry years, farm dams may provide the most frequently occurring perennial habitat for freshwater plants and animals in the Perth Hills, yet because they are on private property, their potential value as drought refuges for native species has not and will not be considered by government departments concerned with freshwater biodiversity conservation. Indeed, little is known Australia-wide about the biodiversity value of farm dams. This is of particular concern given that the south-west of WA is a global biodiversity hotspot, with many unique endemic freshwater species found nowhere else in the world. For example, the Hooting Frog (Heleioporus barycragus) is endemic to the Perth Hills/northern jarrah forest and depends on streamflow to breed and 16 species of dragonfly endemic to southwest WA are found in the Darling Ranges. It is therefore now a matter of urgency to determine what biodiversity is currently supported by farm dams, and then subsequently, how the capacity of farm dams to sustain freshwater biodiversity can be enhanced. Two types of farm dams are common in the Australian landscape: paddock dams that collect rainwater or intersect groundwater/springs; and on-channel dams that collect streamflow. These two types of dams are likely to provide different habitat opportunities for native species, because on-channel dams are connected to streams, whereas paddock dams are not. This difference in connectivity will make it easier for some freshwater animals and plants to colonise on-channel dams. Conversely, this connectivity will also make access easier for exotic plants and animals, which may adversely affect native species. Paddock dams provide more isolated habitat, but can still be colonised by mobile fauna (such as flying insects and birds), wind-blown seeds, and plant and animal propagules arriving in the feathers of waterbirds.
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