Regeneration of degraded woodland remnants after relief from livestock grazing

Clearing for agriculture has left a mosaic of remnants of native vegetation in a matrix of agricultural land. Protection of these remnants is an important issue in minimising the effects of land degradation and for nature conservation in agricultural areas of Western Australia The first approach to restoration is to remove the disturbing element, and in the case of livestock grazing this requires fencing to exclude stock and allow natural regeneration of the remaining vegetation. The description of this natural regeneration process is an essential first step in developing restoration techniques and management strategies for areas of degraded native vegetation. This article describes the changes in the vegetation for three different vegetation types in degraded woodland remnants in south-west Western Australia after livestock grazing has been excluded for seven years. These include vegetation types characterised by the overstorey species including jarrah (Eucalyptus marginata) marri (Corymbia calophylla), wandoo (Eucalyptus wandoo) and sheoak (Allocasuarina fraseriana). Species of the families Poaceae and Asteraceae were dominant in the understorey in grazed remnants for all vegetation types, with the majority of these species being exotics. After seven years, floristic similarity between fenced and grazed plots had decreased while similarity between fenced and ungrazed had increased, in all vegetation types. Native vegetation in jarrah sites have shown the greatest response to cessation of livestock grazing with an increase in species richness and diversity while wandoo and sheoak plots have showed little change. In terms of plant life forms, there was a significant increase in number and cover of native perennial grasses, perennial herbs and shrubs in the fenced jarrah plots. Response of annual species have tended to fluctuate with annual fluctuations in rainfall. There was variation in response to livestock grazing of different vegetation types within these woodland remnants. At a relatively early stage of decline in a remnant, the structure and composition of the native community can be re-established by excluding stock. However, under severe and prolonged grazing, regeneration will be more difficult. These results indicate that the degree of difficulty of restoration will vary for different community types even within the broad category of jarrah and wandoo woodlands. Therefore, when managing for the restoration of remnants of native vegetation, consideration of vegetation type is an important factor.