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

Titre : Grazing impacts in rangelands : assessment of two contrasting landscape types in arid Western Australia from different land management perspectives

Auteur : Pringle, Hugh John Robert

Université de soutenance : Australian National University

Grade : Doctor of Philosophy (PhD) 2001

Résumé partiel
Regional patterns of land use and systems for assessing the "health" of rangelands have not changed their focus from production of meat and fibre, despite ecologically sustainable development becoming the dominant environmental paradigm. In this study I evaluated i) traditional range condition assessment as practised in Western Australia, and explored its capacity to predict changes in ii) biodiversity and iii) landscape patterns and processes along grazing gradients in two contrasting landscape types. I estimated grazing history using a commercially available model and a model based on sheep track density. Although distance from water was a more simple proxy for grazing history, it did not account for as much of the systematic variation in environmental response as either model. Range condition declined with increased grazing in both landscape types, and while the decline was more marked in mulga landscapes, range condition assessments may overestimate degradation in this landscape. Approximately one quarter of plant species were "decreasers" that declined in abundance with increased grazing, compared to 16% that were "increasers". The number of decreaser species also declined with grazing, more rapidly in mulga landscapes than chenopod landscapes. Over a third of ant species (not including singletons) were decreasers in chenopod landscapes. Increaser species in chenopod landscapes, and both decreasers and increasers in mulga landscapes, comprised a relatively minor component of the ant fauna. The sensitivity of the ant fauna to grazing in chenopod landscapes contrasts strongly with conclusions from previous studies in north American rangelands. Overall, grazing suppressed the capacity for landscapes to redistribute and conserve resources in fertile patches. Chenopod landscapes were most profoundly altered : with increased grazing fertile bush mounds decreased in density and proportional area as open areas expanded and became more saline.

Présentation

Version intégrale (290 Mb)