Effects of grazing management and environmental factors on native grassland and grassy woodland, Northern Midlands, Tasmania

摘要

Most remnants of lowland grassland and grassy woodland in Tasmania are grazed by sheep. In some instances, grazed remnants have high conservation value, indicating that grazing and biodiversity conservation are not necessarily conflicting management goals. However, few data exist on the management practices most conducive to maintaining conservation values. The present study examined native grassland and grassy woodland subject to seven different sheep-grazing regimes in the Northern Midlands bioregion of Tasmania and sought to identify the effects of management and environmental factors on vegetation structure and composition. Structural and compositional differences between grassland and woodland, and herbivore scat counts, suggested that grazing disturbance was more intense in grassland than in woodland. Floristic differences within the vegetation appeared to be related to differences in grazing regime. Occurrence of species not commonly observed in grassy vegetation was associated with the resting of pastures in spring, while more intensely grazed sites contained assemblages of species typical of disturbed areas. Exotic invasion was greatest at sites that were not rested and/or had higher stocking rates, and at more eroded sites. Thus, resting and/or low stocking rates were associated with good condition in the grassland and grassy woodland. The nature of differences in vegetation attributes between woodland and grassland suggests that grazer habitat preference increases the differences between these vegetation types. Relatively minor variation in grazing regime was found to have resulted in distinct floristic outcomes, suggesting that the maintenance of a range of management regimes may be conducive to the maintenance of plant species diversity at a landscape scale.