THE EUCALYPT FOREST GRASSLAND GRASSY WOODLAND BOUNDARY IN CENTRAL TASMANIA

Downslope boundaries of forest with grassland and grassy woodland occur over a wide altitudinal range in central Tasmania. Three sites were selected for study of the causes of these boundaries at low, medium and high elevations. The open vegetation was generally associated with moister and less rocky soils and more subdued topography than the adjacent forest. Frost incidence and intensity, soil moisture and waterlogging varied markedly among the three open areas. Planted tree seedlings survived 4 years in the open at all sites, and seedlings established in the open both naturally, and after sowing, where grass competition was reduced by herbicide application, digging or root competition from adult eucalypts. Grazing had no detectable effect on seedling establishment. A pot experiment demonstrated a suppressive effect of native grass swards on both seedling establishment and growth, this effect being largely independent of available moisture and nutrients. While frost, waterlogging, fire and drought may play a role in inhibiting eucalypt establishment and increasing eucalypt mortality at some or all of the sites, the dense grass swards found in all the open areas are considered to be the most likely primary agent of tree exclusion.