The Changing Seasons of the Wetlands

Seasonal Clay-based Wetlands

While the majority of seasonal wetlands in south-west Australia are connected to the regional ground water, there are a series of wetlands found on clay substrates that rely solely on rainwater to fill. These wetlands are characterised by temporally overlapping suites of annual herbs that flower and set seed as the wetlands dry through spring. Over summer the clay substrates dry to impervious pans. The plant communities of clay-based wetlands comprise a flora of over 600 taxa. At least 50% are annual or perennial herbs, 16 occur only on the clay-pans and many are rare or restricted.

The seasonally inundated clays that support these communities are relatively productive agricultural soils and many were cleared soon after settlement. Those that remained intact were largely located on the Swan Coastal Plain in close proximity to metropolitan Perth. In more recent years large areas have disappeared under urban development and today the plant communities of seasonal clay-based wetlands are amongst the most threatened in Western Australia.

Brixton St Wetlands Field Herbarium

One of the most important occurrences of these plant communities, The Brixton Street Wetlands lies only 20km south east of Perth at the foot of the Darling scarp. Most of the wetland soils at Brixton St are water logged through the winter months and deep pools form in clay depressions. When the pools are full they support a number of aquatic plants but as they dry over spring and summer a series of annual and perennial herbs grow, flowers and set seed. The flats surrounding the deeper clay-pans support a diverse range of native herbs, sedges and rushes and slightly higher in the landscape Marri Woodlands cover low sandy rises.