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Influence of cattle grazing practices on forest understorey structure in north-eastern New South Wales

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Abstract

Abstract  In eastern Australia the practice of grazing cattle in eucalypt forests and woodlands, as a supplementary activity to farmland grazing, is widespread. It is typically accompanied by burning at frequent intervals by graziers to promote more nutritious and digestible growth of the ground cover for their livestock. Collectively, these forest grazing practices affect understorey structure, which in turn affects other biotic and abiotic components of these ecosystems. In order to test how significant the effects of forest grazing practices are relative to the effects of other management practices and environmental variables and the degree to which grazing practices determine understorey vegetation structure, we surveyed 58 sites on the northern tablelands of New South Wales, Australia. All sites were located in eucalypt forest and were stratified by grazing status (presence or absence): time since logging, time since wildfire, geology, aspect, slope and topographic position. At each site an index of vegetation complexity and the most abundant plant species were recorded. The data were analysed by a backwards stepwise multiple regression. Grazing practices had the greatest influence on understorey vegetation complexity of any of the measured attributes. The grazed sites were characterized by a significantly lower vegetation complexity score, different dominant understorey species, reduced or absent shrub layers, and an open, simplified and more grassy understorey structure compared with ungrazed sites. Time since logging and time since wildfire also significantly affected understorey structure. Our results indicate that cattle grazing practices (i.e. grazing and the associated frequent fire regimes) can have major effects on forest structure and composition at a regional level.

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