Explaining a sharp transition from sedgeland to alpine vegetation on Mount Sprent, southwest Tasmania

Regular altitudinal sampling of the vascular plant species composition of treeless vegetation on Mount Sprent, Tasmania revealed gradual change between 510 and 820 m, and between 930 and 1050 m, but steep change between 830 and 920 m. The zone of sharp change was the boundary between lowland sedgeland dominated by Gymnoschoenus sphaerocephalus and alpine vegetation. Edaphic and topographic conditions varied relatively little along the transect. Two years of temperature and precipitation data were obtained from sites on either side of the boundary, a site near the summit and a site near the lower limit of the sedgeland. These data indicate that the phytosociological zone of change is coincident with a sharp change in mean temperature conditions between the two central sites. Variation in precipitation appears largely unrelated to phytosociological conditions at this scale. This climatic break appears to be consistent in its characteristics with a frequent subsidence inversion layer, and could explain the similar sharp boundaries found elsewhere on Tasmanian mountains. The phenomenon may be widespread in maritime mountains.