Soil/Landform Unit 65

Open forests of the landscape evident abutting cleared land on lower slopes

Area:

3233 ha

0.24% of CMA region

North of the Gellibrand River,

sandstones and mudstones outcrop in the valleys of Yahoo Creek, Gum Gully Creek and an unnamed creek to the west of Black Bridge Road. These sediments belong to the Moonlight Head Beds of the Otway Group. Slopes are steep and valleys are narrow, in sharp contrast to the rounded hills of adjacent Paleogene sediments. The soils are similar to those found on other outcrops of Cretaceous sediments in the Otway Range, with the exception that surface horizons contain appreciably more sand and the parent material is usually highly weathered. Open forests of

Eucalyptus obliqua

E. ovata

and

E. aromaphloia

are similar to those found on the drier slopes of soil-landform unit

. Most parts of these valleys remain virtually uncleared and quite remote. Hardwood forestry is the main land use, although the rugged terrain makes access difficult. Some softwood plantations have been established in the catchment of Yahoo Creek. Landslips occur on these soils under native forest, and the incidence increases dramatically following clearing. Sheet erosion and gully erosion are also prone to occur.

Cleared gentle lower slopes and swale
	Steep and rugged hills surrounding Yahoo Creek are difficult to manage due to rapid regrowth of vegetation

Component	1	2	3	4
Proportion of soil-landform unit	35%	45%	15%	5%
CLIMATE Rainfall (mm)	Annual: 850-1000, lowest January (40), highest August (130)
Temperature (^oC)	Annual: 12, lowest July (7), highest February (18)
Seasonal growth limitations	Tempreature: less than 10^oC (av.) June-September Precipitation: less than potential evapotranspiration November-March
GEOLOGY Age and lithology	Cretaceous highly feldspathic fluvio-volcanic sandstone and mudstone (Moonlight Head Beds); minor Paleogene marine glauconitic sand
Geomorphology	3.1.2 Deeply dissected upland ranges of the Souther Uplands
LANDUSE	Uncleared areas: Hardwood forestry for sawlogs, poles and posts; nature conservation; water supply Minor cleared areas: Sheep and cattle grazing; water supply
TOPOGRAPHY Landscape	Deeply dissected hills to the north of Gellibrand River
Elevation range (m)	60-270
Local relief (m)	110
Drainage pattern	Dendritic with small radial areas
Drainage density (km/km²)	2.4
Landform	Hills
Landform element	Steep slope	Crest and upper slope	Slope	Swale and gentle lower slope
Slope and range (%)	50 (20-70)	15 (2-30)	35 (15-45)	13 (1-25)
Slope shape	Linear	Linear	Linear	Concave
NATIVE VEGETATION Structure	Open forest	Open forest	Open forest	Open forest
Dominant species	E. ovata, E. obliqua, E. radiata, E. aromaphloia, E. viminalis	E. obliqua, E. ovata, E. aromapholia, E. radiata	E. viminalis, E. obliqua	E. viminalis, E. obliqua, Acacia melanoxylong
SOIL Parent material	In situ weathered sandstone and mudstone, colluvial rock	In situ deeply weathered sandstone and mudstone	In situ weathered sandstone and mudstone	Colluvium
Description (Corangamite Soil Group)	Stony brown gradational soils (7)	Yellow-brown gradational soils, coarse structure (7)	Brown gradational soils (7)	Dark brown gradational soils (7)
Soil type sites	OTR732	OTR750	OTR414, OTR416, OTR736	OTR428, OTR736
Surface texture	Fine sandy loam	Sandy clay loam	Loam	Loam
Permeability	High	Low	Moderate	Moderate
Depth (m)	0.7	1.2	0.9	>2
LAND CHARACTERISTICS, POTENTIAL AND LIMITATIONS	Stony shallow soils with weak structure and low water holding capacity on steep slopes are prone to sheet erosion and landslides.	Soils of low permeability on the steeper slopes are prone to sheet and rill erosion. Dispersible subsoils are prone to gully erosion.	Clay subsoils on steep slopes subject to periodic saturation are prone to landslips. Steep slopes are prone to sheet erosion.	Weakly structured soils receiving runoff from adjacent hills are prone to scour gullying siltation and flooding.

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