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.