EFFECTS OF LANDSCAPE FRAGMENTATION ON ECOSYSTEM PROCESSES IN THE WESTERN-AUSTRALIAN WHEAT-BELT

The effects of landscape fragmentation are usually considered in terms of biogeographic changes and habitat loss. I argue here that the effects of fragmentation on ecosystem processes are just as important to the long-term conservation of biota in remnant areas. In the Western Australian wheatbelt, widespread rapid clearing for agriculture has removed most of the native perennial vegetation and replaced it with an agricultural system based predominantly on annual crops and pastures. Fragmentation of the natural system has led to large changes in the water and nutrient cycles, radiation balance and wind regimes of the region. Removal of perennial vegetation has reduced evapotranspiration and altered soil water flows, such that peak runoffs have increased and water tables have risen, bringing stored salt to the surface. Salinity and waterlogging problems have resulted. The agricultural system has a very open nutrient cycle compared with the native vegetation. Changed vegetation covers have altered the radiation balance, and temperature and humidity gradients are apparent al the edges between remnants and agricultural land Similarly, lack of perennial cover increases the wind speed near the ground and leads to increased soil erosion. These changes in the landscape impinge on the remaining fragments of native vegetation, and management of external influences is probably more important than management of internal processes within remnant areas. Remnant vegetation management has to be carried out in the context of the overall landscape.