Study Area
The study area encompassed the South East Highlands and Australian Alps Bioregions of the state of NSW, Australia (Thackway & Creswell, 1995), an area of 96,089 km2 encompassing mountains and plateaus of the Great Dividing Range. Average annual precipitation ranges from 460 —- 2,344 mm and mean annual temperatures are 3 – 16o C. The area is underlain by a complex series of heavily folded metamorphosed sedimentary rocks deposited from the Ordovician to Devonian periods and interspersed with numerous granite intrusions and, to a much lesser extent, basalts deposited in the Paleogene.
Primary factors influencing the distribution of vegetation formations in our study area include temperature, rainfall, topography, soils and drainage (Jenny, 1983; Costin, 1954; Beadle, 1981; Keith, 2004). Alpine assemblages are restricted to elevations more than 1830 m above sea level where winter temperature minima fall below the physiological tolerance of trees (Keith, 2004). Tree cover progressively increases with decreasing elevations severity of winter conditions declines. Sub-alpine grassy woodlands occupy the sub-alpine tracts, characteristically with short gnarled trees and a large compliment of cold-tolerant species also found in the alpine zone. On the southwest flank of the Great Divide, sub-alpine woodlands grade into tall wet sclerophyll forests, sustained by high orographic rainfall originating in south-westerly air flows. To the east, depending on soils lithology texture and fertility, sub-alpine woodlands grade into either Dry Sclerophyll Forest or Grassy Woodlands as annual rainfall declines in the shadow of the Divide. Grasslands replace Grassy Woodlands in frost hollows, the heaviest-texture soils and the most moisture-limited sites (Costin, 1954). Further east of the tablelands, grasslands and grassy woodlands are replaced by mosaics of wet and dry sclerophyll forests on the escarpment ranges as rainfall increases with increasing elevation and exposure to oceanic weather systems (Keith, 2004). Wetlands occur throughout the bioregions in areas of impeded drainage, while heathlands are among the local expressions of edaphic and topographic variation.