La Trobe (Le)

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system La trobe- geo

Area: 707 sq. km (3.5%)

La Trobe land system is mapped on hilly terrain with Ordovician, Devonian and Silurian sediments. It occurs mainly in the south-west of the East Victorian Uplands. Topography is of the ridge-and-ravine type although some ridge crests are rounded; slopes are steep and moderately long. This land is similar geologically and topographically to the Wonnangatta land system but is much more humid.

Deep, well-structured soils result from the combination of high rainfall, medium- and fine-grained sedimentary rocks and less-active soil creep. Both gradational and duplex type soils are common, with the former probably dominant. The soils tend to be leached, acidic and probably of low fertility.

Shrubby open forest II predominates. The vegetation on protected slopes or in local drainage depressions varies from shrubby or layered open forest III or IV to closed fernland.

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system La trobe- image

Timbered hillslopes, typical of La Trobe land system, with cleared alluvial terraces in the foreground.

CLIMATE Rainfall, mean (mm) Temperature, mean (°C) Seasonal growth limitations	Annual 800 - 1400; lowest January or February (50 - 90), highest August or September (120 - 180) Annual 8 - 12; lowest July (3 - 7), highest February (16 - 20) Temperature <10°C (av.): April - October Rainfall < potential evapotranspiration: January, February; occasional winter snow
GEOLOGY Age, lithology	Ordovician, Silurian and Devonian sandstones, siltstones and claystones
PHYSIOGRAPHY Landscape Elevation range (m) Relative relief (m) Drainage pattern Drainage density (km/km²)	Steep hills with ridge-and-ravine topography 100 - 1080 100 - 260 Dendritic 1.3
PRESENT LAND USE	Mostly uncleared: hardwood forestry (minor timber products); apiculture; bush grazing of cattle. Minor proportion cleared: grazing of dairy and beef cattle

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system La trobe- cs

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system La trobe- graph

LAND COMPONENT Percentage of land system Diagnostic features	1 75 Exposed slopes	2 10 Protected slopes	3 5 Broad rounded ridge tops	4 5 Peat and organic deposits in seepage-fed minor drainage depressions	5 5 Terraces along major valley flats
PHYSIOGRAPHY Slope %, typical and (range) Slope shape	20-25, (10 - 60) Straight	20 - 25, (10 - 60) Straight	5 - 10, (0 - 15) Convex	<2, (0 - 5) Concave	<2, (0 - 5) Straight or concave
SOIL
Parent material	Mudstone, siltstone, sandstone and shale			Locally derived alluvium and colluvium	Mixed alluvium
Description	Generally dark sandy loam to sandy clay loam topsoil with crumb structure; yellowish brown or red clay subsoil, acidic and usually with medium blocky structure. Occasionally shallow and stony; profiles gradational or duplex			Shallow peat and mineral soils with high surface organic matter	Variable; red gradational soils; brown undifferentiated stratified sand to sandy clay loams
Classification	Yellow and Red Podzolic Soils, Lithosols Gn4.11, Gn4.81, Gn4.51, Gn4.64, Gn2.81, Gn3.34, Dy3.21, Dy3.41, Dy5.21, Um4.13, Um6.46			Brown Earths, Acid Peats Gn4.52, O	Alluvial Soils, Red Earths Gn2.41, Um6.14, Uc1.41
Surface texture	Fine sandy loam to clay loam			Sandy loam to clay loam	Sand to sandy clay loam
Surface consistence	Slightly hard when dry, friable when moist			Friable when moist	Variable
Depth (m)	0.8 - 2.0, in places very shallow			>2.0	>2.0
Nutrient status	Low			Low	Low
Available soil water capacity	Moderate			Moderate	Variable
Perviousness to water	Slow to moderate			Moderate	Moderate to rapid
Drainage	Good			Very poor to poor	Often good
Exposed stone (%)	Generally 0			0	0
Sampled profile number	-			-	-
NATIVE VEGETATION Structure of vegetation and characteristic species of dominant stratum (+ Predominant species)	Shrubby open forest II: E. sieberi+, E. obliqua+; one or more of E. baxteri E. cypellocarpa, E. radiata, and E. dives usually associated	Shrubby or layered open forest III: E. cypellocarpa+, E. obliqua+, usually with E. radiata, E. sieberi	Shrubby or layered open forest II: E. cypellocarpa+, E. obliqua+, E. sieberi, sometimes E. consideniana+	Limited data — probably closed fernland of Dicksonia antarctica	Open forest III, IV, often layered: E. viminalis+, E. cypellocarpa, E. obliqua, E. radiata

Disturbance	Affected process and trend	Primary resultant deterioration			Casual activities	Primary off-site process
Disturbance	Affected process and trend	Form	Susceptibility of components	Incidence with components	Casual activities	Primary off-site process
Alteration of vegetation: — reduction in leaf area, rooting depth and/or perenniality — reduction in density of tree roots	Reduced transpiration, resulting in increased deep percolation Decreased root-binding	Nutrient loss Soil creep	Not determined 1,2; moderate	Not determined Uncommon	Removal of trees Accelerated by major disturbance of the native vegetation	Increased movement of water to groundwater; increased base-flow of streams Increased sediment load
Increased exposure of surface soil	Increased overland flow and soil detachment	Sheet and rill erosion	1,2,3; moderate	Uncommon	Clearing, logging, burning, overgrazing, road building and other earth-moving activities, trafficking by stock and vehicles.	Increased flash flows and sediment load.
Increased physical pressure on soil	Increased compaction With reduced infiltration	Structure decline Sheet and rill erosion	1,2,3; low - moderate 4; high 5; moderate 12,3; moderate	Uncommon Uncommon	Increased trafficking, export of organic matter As for sheet and rill erosion above	- Increased flash flows
Increased soil disruption	Increased soil break-up	Gully erosion Streambank erosion	12,3; moderate 5; high	Uncommon Uncommon	As for sheet and rill erosion above As for sheet and rill erosion above	Increased sediment load Increased sediment load
Comments: Soil creep has been observed on a steep slope in this land system

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