Birregun (Be)

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

Area: 1968 sq. km (9.7%)

Birregun land system is particularly extensive, occurring on Ordovician. Devonian and Silurian sediments in the upper parts of the East Victorian Uplands, below the subalpine tract. The terrain is mountainous with ridge and-ravine topography and long, steep slopes on which soil creep and other slope processes are active. Birregun land system is similar in geography and topography to Talbotville land system but is much more humid and has associated differences in the vegetation and soils.

This environment with high rainfall, steep slopes and active slope processes has tended to produce leached. uniformly-textured soils, which are often stony, shallow, permeable, well structured and moderately acidic.

Most of the vegetation is shrubby or layered open forest II or III, with open forest I or II on lower, drier slopes.

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

Mountain slopes clearly showing the characteristic ridge-and-ravine topography

CLIMATE Rainfall, mean (mm) Temperature, mean (°C) Seasonal growth limitations	Annual 900 - 1600; 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: February; frequent winter snow
GEOLOGY Age, lithology	Ordovician, Silurian and Devonian siltstones, sandstones and shales; minor proportion lightly metamorphosed
PHYSIOGRAPHY Landscape Elevation range (m) Relative relief (m) Drainage pattern Drainage density (km/km²)	Steep mountains with ridge-and-ravine topography 180 - 1600 180 - 740 Dendritic 1.4
PRESENT LAND USE	Uncleared: hardwood forestry; bush grazing of cattle: apiculture: small areas included in Baw Baw and Bogong National Parks

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

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

LAND COMPONENT Percentage of land system Diagnostic features	1 75 Slopes with humid forest (non-ash species)	2 10 Slopes, usually at lower elevations, with drier forest	3 10 Protected slopes with alpine or mountain ash	4 5 Discontinuous terraces along major streams
PHYSIOGRAPHY Slope %, typical and (range) Slope shape	30 - 50. (25 - 80) Straight	30 - 50, (25 - 80) Straight	40 - 50, (30 - 100) Straight	<5, (0 - 10) Straight
SOIL
Parent material	Siltstone, sandstone and shale			Coarse textured alluvium
Description	Black to very dark loam to sandy clay loam merging into greyish brown or brown sandy clay loam to light clay: mostly shallow and very stony	Similar to component 1, but often less shallow and subsoil more reddish	Similar to component 1, but generally deeper and surface soil often with more humus and darker coloured	Limited observations — mainly very dark loamy sand to sandy loam; stony
Classification	Lithosols, Brown Earths Um1.23, Um1.44, Um5.51. Um6.23, Um6.24. Um7.11, Gn3.21	Red Earths. Lithosols, Brown Podzolics Um6.12, Um6.24, Db1.21	Brown Earths, Lithosols, some Alpine Humus Soils at higher elevations Um6.14, Um6.21, Um6.23, Um7.11, Uc6.14, Gn4.11	Alluvial Soils Uc1.21, Uc5.21
Surface texture		Loam to sandy clay loam		Loamy sand to sandy loam
Surface consistence		Soft to slightly hard		Soft to slightly hard
Depth (m)		Extremely variable; 0.2 - 1.5		<2.0
Nutrient status		Low		Low
Available soil water capacity		Moderate		Moderate
Perviousness to water		Rapid		Rapid
Drainage		Good		Good
Exposed stone (%)		Very variable; 0 - 60		Variable
Sampled profile number	-	7	-	-
NATIVE VEGETATION Structure of vegetation and characteristic species of dominant stratum (+ Predominant species)	Shrubby or layered open forest II, III: Usually mixed forests with composition and predominant species variable — E. cypellocarpa, E. dives. mannifera. E.obliqua, E. rubida	Open forest 1, II: Pure or mixed stands of E. dives, E. sieberi, E. obliqua; E. mannifera sometimes associated	Shrubby or layered open forest III: Higher elevations — E. delegatensis+, occasionally with E. dives+, and/or E. rubida+ Lower elevations — E. regnans (presumed)	Shrubby open forest II: Variable composition, commonly E. rubida+ or E. viminalis+ with or without 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: a) increased deep percolation and leaching b) increased regolith wetness Decreased root-binding	Nutrient loss Soil creep Soil creep	Not determined 1,2,3: moderate - high 1,2,3: moderate - high	Not determined Common Common	Removal of trees Logging and burning Logging and burning	Increased movement water to groundwater: increased base-flow of streams Increased sediment lc
Increased exposure of surface soil	Increased overland flow and soil detachment	Sheet and rill erosion	1.2,3: high	Uncommon	Clearing, logging, burning, overgrazing, road building and other earth-moving activities.	Increased flash flows and sediment load.
Increased physical pressure on soil	Increased compaction With reduced infiltration	Structure decline Sheet and rill erosion	12.3.4: low - moderate 1.2.3: high	Uncommon Uncommon	Increased trafficking, overgrazing, export of organic matter As for sheet and rill erosion above	- Increased flash flows and sediment load
Increased soil disruption	Increased soil break-up	Gully erosion Streambank erosion	1,2,3: high 4: high	Uncommon Uncommon	As for sheet and rill erosion above As for sheet and rill erosion above	Increased sediment load Increased turbidity of streams
Comments: Regeneration of vegetative cover is generally rapid because of adequate rainfall, but is limited at higher elevations

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