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Birregun (Be)

A study of the land in the Catchment of Gippsland Lakes - Vol 2 - land system Birregun- geoArea: 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 <10C (av.): April - October
    Rainfall < potential evapotranspiration: February; frequent winter snow
GEOLOGY
Age, lithology
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- csA 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
Form
Susceptibility of components
Incidence with components
    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 erosion1.2,3: highUncommonClearing, 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-upGully 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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