Wonga Land System

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Adjacent to the lateritic plateau around Simpson and at a similar elevation, a gently undulating plain without lateritic ironstone extends eastwards towards Barongarook. The parent material is mainly Tertiary sand and clay, with some minor redistribution on sand veneers in some parts and outcrops of deeply weathered Cretaceous sandstone along the sides of some of the drainage lines.

The soils exhibit similar mottling and deep weathering to those found in the Simpson land system, and are prone to nutrient deficiencies and phosphate fixation. Open forests of Eucalyptus obliqua occur over most of the landscape, although E. baxteri tends to dominate on the polygenetic soils with hardpans. Acacia mucronata acts as a strong indicator of the presence of Cretaceous outcrops.

Most areas remain uncleared and are selectively logged for hardwood timber, although most timber is of insufficient size to provide good sawlogs.

A Study of land in the catchments of the Otway Range and adjacent plains - wonga

The cleared area in the foreground contrasts with the native
hardwood forests.

Area: 72 km²	Component and its proportion of land system
Area: 72 km²	1 45%	2 7%	3 25%	4 15%	5 8%
CLIMATE Rainfall, mm	Annual: 850 – 950, lowest January (40), highest August (120)
Temperature, 0^oC	Annual: 13, lowest July (8), highest February (18)
	Temperature: less than 10^oC (av.) June – August
	Precipitation: less than potential evapotranspiration late October – March
GEOLOGY Age, lithology	Paleocene marine unconsolidated clay, silt and sand				Lower Cretaceous feldspathic sandstone and siltstone
TOPOGRAPHY Landscape	Undulating plain in the north part of the Gellibrand River catchment
Elevation, m	120 – 340
Local relief, m	30
Drainage pattern	Parallel and dendritic
Drainage density, km/km²	1.2
Land form	Undulating plain
Land form element	Crest, upper slope	Colluvial fan, depression	Slope	Lower slope	Lower slope, drainage line
Slope (and range), %	7 (0-12)	4 (0-7)	7 (1-16)	10 (4-14)	10 (4-14)
Slope shape	Convex	Concave	Convex	Linear	Linear
NATIVE VEGETATION Structure	Open forest	Open woodland	Open forest	Open forest	Open forest
Dominant species	E. obliqua, E. radiata, E. baxteri, occasionally E. ovata, E. viminalis, E. aromaphloia	E. baxteri, E. ovata, E. nitida	E. baxteri, E. radiata, E. ovata, E. obliqua, occasionally E. aromaphloia	E. obliqua, E. radiata, E. ovata, E. baxteri	E. obliqua, E. ovata, E. radiata, E. aromaphloia
SOIL Parent material	Clay, silt and sand	Colluvial sand on sand, silt and clay	Colluvial sand on sand, silt and clay	Clay, silt and sand	In-situ weathered rock
Description	Mottled yellow and red gradational soils	Grey sand soils, weakly structured clay underlay	Grey sand soils, structured clay underlay	Yellow-brown gradational soils, coarse structure	Yellow-brown gradational soils, coarse structure
Surface texture	Sandy loam	Sandy loam	Sandy loam	Sandy loam	Fine sandy clay loam
Permeability	Moderate	Low	Low	Low	Low
Depth, m	>2	>2	>2	>2	1.5
LAND USE	Uncleared areas: Hardwood forestry for sawlogs, posts and poles; water supply; nature conservation; gravel extraction. Minor cleared areas: Beef cattle grazing; dairy farming
SOIL DETERIORATION HAZARD Critical land features, processes, forms	Low inherent fertility and phosphorus fixation lead to nutrient decline.	Low permeability and perched water tables lead to seasonal waterlogging and soil compaction.	Low inherent fertility and leaching of permeable surfaces lead to nutrient decline. Low permeabilities lead to seasonal waterlogging and soil compaction.	Dispersible clay subsoils of low permeability are prone to gully erosion. Steeper slopes are prone to sheet erosion.	Dispersible subsoils receiving run-off from adjacent areas are prone to gully erosion.

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