Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Remotely sensing changes in the vegetation of ephemeral wetlands

Auteur : Benger, Simon

Université de soutenance : Australian National University

Grade : Doctor of Philosophy (PhD) 2001

Résumé partiel
The ephemeral wetlands of semi-arid Australia provide impo1iant habitats for many species and play a significant role in the hydrological and biological regimes of these environments. As most inland wetlands owe their existence to unregulated cycles of flooding and drying, many wetlands are now being forced into decline through flow regulation associated with irrigation for large, highly productive agricultural enterprises. This decline usually manifests itself through reductions in the spatial extent of vegetation stands, transitional effects in the landscape and a deterioration in the physiological condition of individual plants. A timeseries of Landsat TM and JERS-1 optical and radar imagery were used to investigate the potential for employing various vegetation species as remotely sensed indicators of wetland decline in the Macquarie Marshes of central western New South Wales. The research examined the utility of remotely sensed imagery for the mapping of semi-arid inland wetland vegetation and assessed its effectiveness in detecting changes in the physiological health of wetland vegetation due to alterations in the hydrological regime. Four species, river red gum Eucalyptus camaldulensus, cumbungi reed Typha orientalis, common reed Phragmites australis, and water cooch Paspaulum paspalodes could be detected at sufficient spatial and spectral resolution to be mappable from satellite imagery. All of these species showed changes in spectral characteristics and radar response as a result of reduced flooding of the wetlands. Two of the species examined, cumbungi reed and common reed, worked well as indicators of short term changes in water availability by manifesting loss of spatial extent and reduction in NDVI. River red gum stands were excellent indicators of longer term decline due to their relative permanence in the landscape and longer response to changes in water availability, while the condition of water cooch pastures was also a good indicator of wetland condition. The development of these techniques offers good potential to facilitate monitoring of the physiological health of inland wetlands and assist in management decisions regarding flow regulation and flood control.

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