|
Impacts of grazing on induced short tussock grasslands
Short tussock grasslands occur where disturbance (e.g. grazing, burning) or environmental stress (e.g. soil moisture deficit) prevents the short tussocks from being out-competed by taller, more stable vegetation types, such as tall tussocks and woody species. Grazing impacts on the vegetation, and therefore plays an important role in preventing such succession.
Short tussock grasslands usually have some exotic plants growing within the community. In moist sites where the intertussock spaces are dominated by exotic plants, grazing will keep the palatable exotic plants at bay, thereby reducing competition (Lord, 1990). Grazing can also control palatable woody weeds.(Meurk et al., 1989). This not only benefits the native plants present in the grassland, which are easily smothered by such competitive grasses, but native insect fauna may also benefit (White 1991). Grazed short tussock grasslands therefore generally have greater species diversity of both native and exotic vascular and non-vascular plants (Meurk et al.,1989).
Grazing adversely effects short tussock grasslands by reducing the cover of palatable native plants (Lord, 1990). Meurk et al.(1989) suggested that in some situations, it may be feasible to reduce competition of exotic species by mowing, cutting, weeding or burning. These methods may be preferable to grazing as they do not discriminate against palatable native species Tussock size can also be reduced when over-grazed.
Short tussock grasslands dominated by native plants, in dry areas do not benefit from being grazed. For example, Meurk et al. (1989) noted that the grazing of a dryland Rytidosperma grassland on the Canterbury Plains, resulted in a reduction of native vascular plant species in favour of non-vascular species. The presence of stock results in increased nutrient cycling (i.e. through the urine) which favours the more competitive adventive intertussock grasses.
A reduction in grazing pressure results in an increase in tall statured vegetation, including snow tussocks and native scrub species (Hunter and Scott, 1994; Rose, 1983).
| |