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CHaPTeR 1 Introduction to the project
This bioregion has a generally temperate to cool temperate climate with smaller areas of
montane climate at higher altitudes. Mean annual temperatures range from 9 to 17˚ C. Annual
rainfall averages between 653 and 1765 mm and is generally summer dominant, although in the
montane areas it is relatively evenly distributed throughout the year.
The geology of the bioregion is characterised by mainly Permian sedimentary rocks which
have undergone extensive uplifting and faulting. Extensive basalt flows cover large parts of
the tablelands and granite intrusions occur in many areas. The topography is one of stepped
plateaux which extend east and south to the escarpment where coastal streams form deep,
steep-sided gorges. The granite intrusions form steep country with numerous boulders and tors
in the surrounding plains of level basalt flows.
Soils vary depending on parent material, topography and rainfall, with the granite-derived soils
forming sandy, low-fertility soils of generally poor structure which tend to be highly erosive.
The basalt-derived soils tend to form shallow loams on steeper sites and richer clay loams on
flatter sites ranging from red-brown to brown to black depending on topographic position.
Where the Permian sedimentary rocks are exposed these tend to form relatively infertile, texture
contrast soils.
1.4.3.5 Other bioregions within the study area
Of the remaining bioregions included within the study area the Nandewar bioregion occurs
only as a narrow strip in the north within the 1500 m buffer used for data collation and survey
purposes (see Figure 1.2) and is not considered in this section. The New South Wales South
Western Slopes bioregion extends into a small area in the far west of the study area around the
township of Mudgee (see Figure 1.2). The climate of this bioregion is sub-humid with mean
annual temperature ranging from 11 to 17˚ C, reaching its maximum in the west outside of the
study area. Mean annual rainfall is variable across the bioregion, decreasing to the west, and is
highest (up to around 1200 mm) within the study area but decreasing to around 400 mm west
of the study area.
Topographically the bioregion consists of low ranges and slopes of the western fall country
of the Great Dividing Range. The geology of the bioregion is dominated by Cambrian to
Carboniferous meta-sediments and granites which have been extensively folded in a northwesterly
direction. Soils range from shallow, stony soils on the ridges and texture contrast soils
on the slopes with sandy or loamy alluvial soils on the valleys. The alluvial soils are frequently
poorly drained and subsoils may accumulate salts.