Tamar report land Capability Survey of Tasmania k e noble 1992 Tamar Report

64

*Soil Association names from Beaconsfield Soil Survey (Dimmock, unpublished)

Figure 10:

Relationship between land capability classes mapped on coastal windblown sands.

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65

Class 5 land on sandstones, slates and quartzites

This type of Class 5 land occurs on older, indurated rock types, including Ordovician,

Cambrian and Precambrian sandstones, slates, greywackes, siltstones, conglomerates and

quartzites.

Localities where this type of land have been mapped are around Beaconsfield, Punchs

Terror, and on lower slopes of the Asbestos and Dazzler Ranges, and Mt Careless.  Annual

rainfalls range between 700 and 1 000 mm.

Soil associations which occur on these rock types are the Asbestos and Norton Associations

from the Beaconsfield Soil Survey (Dimmock, unpublished).  These soils are stony

gradational soils which have sandy surface horizons overlying yellow-brown clay.  Rock

fragments of quartz or quartzite are often scattered over the soil surface.

Slopes are generally between 18 and 30%.  The sandy and stony nature of the soils

combined with low natural fertility and erosion hazard limit this type of land to grazing

purposes.  Photo 16 shows an example of this type of Class 5 land.

Photo 16:

Class 5 land on Ordovician siltstone and conglomerate.  Tamar map 804237.  Frankford Road.

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66

Class 5 land on sandstones, siltstones and mudstones

Class 5 land has also been mapped on sandstones, siltstones and mudstones of Triassic,

Permian and lower Palaeozoic ages, including Mathinna Beds.  The majority of slopes

range between 18 and 30%, which are steeper than on similar deposits mapped as Class 4

(refer to Figure 8).  Some areas on gentler slopes may be cultivated for pasture

establishment or renewal, but are not suitable for cropping because of the high erosion risk.

The steeper slopes often occur around the edges of dolerite bodies, which has protected

them from extensive erosion.  Average annual rainfalls range between 800 and 1 000 mm.

Localities where this type of land occur are at Lefroy (Mathinna Beds); Notley Hills and

north and east of Parkham (Triassic sandstone), and at Winkleigh, Glengarry, Holwell,

Stewarts Hill, Frankford, West Frankford, Notley Hills and Thompsons Hill (Permian

sandstones, siltstones and mudstones).

This type of land has a range of soils associated with it because of the complexity of the

alternating bands of sandstone, siltstone and mudstone which influence the soil type.

Soil associations which occur on this type of land are the Holwell Association and the

steeper slopes of the Warrina and Tatana Associations (from the Beaconsfield Soil Survey;

Dimmock, unpublished).

The Tatana Association occurs on the Permian and Triassic sandstones.  These soils are

predominantly sandy podzols.  A typical profile may have a dark grey loose sandy A1

horizon; over a brownish grey loose sandy A2 horizon; over a dark brown organic

cemented sand (organic B horizon); over mottled brown clayey sand or sandy clay loam.

The soils of the Holwell Association are the most extensive and occur on the Permian

mudstones and siltstones.  They occur on the steeper slopes and overlap with the Warrina

soils on lower slopes.  Soil profiles are generally gradational on the Holwell Association

and duplex on the Warrina Association.  The Warrina soils are similar to those described in

Class 4 (Refer to Page 53.)  In comparison, the Holwell soils are darker and generally have

not developed an A2 horizon.  A typical profile on the Holwell Association may have a

dark grey-brown loam or fine sandy loam A horizon, over a dark grey-brown clay B

horizon.

The soils formed on Mathinna Bed sandstones and siltstones generally have shallow

surface horizons, with a sandy and loose subsurface over clay.  In some areas (e.g. around

Lefroy), abundant quartz gravels are present.

The soils formed on sandstones are infertile, strongly leached and require high fertiliser

inputs to maintain good pastures for grazing.  The soils formed on mudstones have better

structure but still require supplementary fertiliser inputs.

Soil slip, sheet and gully erosion are the dominant erosion forms.  There are also several

historic slump (mass movement features) associated with the Permian sediments (e.g.

Stewarts Hill area).

Slope, erosion hazard and low fertility combine to make these areas Class 5 land.  Photo 17

shows an example of this type of land.

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67

Photo 17:

Class 5 land on Permian sandstones, siltstones and mudstones.  Class 4 land in foreground.

Tamar map 804237.  Frankford Road.

Other Class 5 land

Other areas of Class 5 land have been mapped on limestone and ultrabasic rocks.

Class 5 land on limestone has been mapped in the Flowery Gully locality on slopes

between 20 and 35%.  Soils are red and well structured, typical of Terra Rossa soils which

form from weathering Karst limestones.  Soil depths can vary in relation to the underlying

rock, from a few centimetres to over one metre.  The Soil Association mapped is the

Flowery Gully Association from the Beaconsfield Soil Survey (Dimmock, unpublished).

Sink holes and caves are common features formed by the dissolution of the limestone

which contains very high amounts of calcium carbonate.  A combination of steep slopes,

broken terrain, sink holes and shallow soil depths in places, make this type of land Class 5.

A small area of Class 5 land has also been mapped on igneous and metamorphic rocks of

the Andersons Creek Ultramafic Complex.  This type of land has been mapped at Barnes

Hill and Simmonds Hill, south west of Beaconsfield.  Slopes are generally greater than

20%.  Soils are variable because of the range of parent materials on which they are formed,

but have been mapped as the Vulcan Association (Beaconsfield Soil Survey; Dimmock,

unpublished).  Large amounts of ironstone gravel, cemented laterite and rock outcrops are

common.

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68

10.6 Class 6 (26 038 ha: 14.30%)

Class 6 land has been mapped on a range of parent materials including windblown sands,

dolerite, mudstones, sandstones, quartzites, slates, conglomerate and quartz gravels.

Class 6 land on Dolerite

Class 6 land on dolerite is common in all the dolerite areas on the map sheet.  The major

localities are Mt George, Tippogoree Hills, Stockyard Hills, Sidmouth to Bradys Lookout,

Rubicon Hills, Wurra Wurra Hills, Drys Sugarloaf, Christmas Hill, Stephens Hill, Black

Sugarloaf, Black Sugarloaf Ridge, Brushy Rivulet, The Tump, The Stony Rises and Grassy

Hut Tier.

Class 6 on dolerite generally occurs on steeper slopes (35%), and the amount of dolerite

boulders present is significantly more than on similar land mapped as Class 5 (refer to

Figure 9 and Photo 18).  Annual rainfalls range between 700 and 1 000 mm.

The major soil type mapped in the Beaconsfield Soil Survey (Dimmock, unpublished), is

the Eastfield Soil Association as described for Class 5 land on dolerite (Page 60).  However

profile depths are generally shallower with a significant increase in the amount of dolerite

boulders throughout the profile and over the surface of the land.

This type of land is marginal for grazing purposes, because of the amount of rock outcrops

present.  It is used extensively as run country for sheep.  Because of the amount of boulders

present, improvement of native pastures is not possible by surface cultivation methods.

Photo 18:

Class 6 land on dolerite.  Tamar map 801060.  North of Exton.

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69

Class 6 land on Windblown Sand

Class 6 land on windblown sand deposits has been mapped on the higher dune ridges of the

coastal plain, between George Town and Beechford, and at Greens Beach and Port Sorell.

Annual rainfalls in these areas range between 700 and 800 mm.

Refer to Photo 19 for an example of this type of land, and to Figure 10 for a diagrammatic

representation of the relationship between land capability classes mapped on windblown

sands.

Soil associations mapped in the Beaconsfield Soil Survey (Dimmock, unpublished), which

relate to this class of land are the Dalrymple and Kelso Associations (sand podzols and

weakly podzolised calcareous sands).  The weakly structured and very poorly developed

soils are free draining with low moisture holding capacities, low organic matter content,

and are subject to severe summer drought.  Soils also have low pH and require high

fertiliser inputs for grazing purposes.

These areas are highly susceptible to wind erosion if the vegetation cover is disturbed or

broken.  Most areas are presently stabilised with vegetation, but further development into

pasture should be restricted because of the severe erosion hazard.  This erosion hazard can

be mainly attributed to the following conditions, all of which discourage plant growth:

exposure to strong salt-laden winds, the unstable nature of the sand dunes, severe soil

moisture deficiencies, very weak soil development and nitrogen deficiency.  Eroded areas

require stabilisation with suitable vegetation (e.g. marram grass), and prevention of stock

trampling, grazing and vehicle access in these areas is critical for protection against wind

erosion.

In some areas (e.g. Cimitiere Plain and Beechford area) it was difficult to separate the

higher, recent dune areas with little soil development, from more stabilised areas, because

of the intricate mosaic of dunes and swales.

The severe wind erosion potential of these areas combined with poor soil development and

infertile soils, combine to make this type of land marginally suitable for grazing purposes.

Photo 19:

Class 6 land on windblown sand.  Class 5 land in foreground.  Tamar map 932563.  Settlement

Road.

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Class 6 land on sandstones, slates and quartzites

This type of Class 6 land has been mapped on the flanks of the Asbestos Range, south of

Badger Head and west of York Town, Cabbage Tree Hill (Beaconsfield), slopes between

the Dazzler Range and Mt Careless, and at Punchs Terror (south of Dunorlan).

Geology and soil types are the same as those mapped on Class 5 land on sandstones, slates

and quartzites (Page 64).  However slopes are steeper than those mapped on Class 5, and

can range between 30 and 45%.  Soils are generally shallower and stonier, with some

profiles consisting predominantly of rock fragments.  Average annual rainfalls range

between 700 and 1 000 mm.

The steep slopes and shallow, stony soils make this type of land marginally suitable for

grazing purposes.

Other Class 6 land

Class 6 land on rounded quartz and quartz conglomerate occurs around the Beaconsfield

Reservoir, and along Kelso Road, and Badger Head Road.  These areas have obvious signs

of disturbance and have been mined for the quartz gravels for road building.  Because of

this disturbance there are very few areas with typical soil profiles of the Beaconsfield

Association (Beaconsfield Soil Survey; Dimmock, unpublished).  Although slopes are not

steep (usually less than 30%), the amount of interference with these soils have rendered

them suitable only for rehabilitation for marginal grazing purposes.

Class 6 land has also been mapped on steep gorges or scarp edges in mudstone, sandstone

or siltstone hill country around Stewarts Hill, and West Frankford localities.  Soils are the

Holwell Association, similar to those on Class 5 land on the same parent material -

however they are generally shallower because of the steeper slopes and removal of soil

material by erosion.  Some of these areas are mapped along the cliff or scarp edges of

historic slump features.

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71

10.7 Class 7 (874 ha; 0.48%)

Class 7 land has been mapped on windblown sands along the coast, and on very steep

slopes on quartzites, greywackes and slates.  All Class 7 land is unsuitable for agricultural

use.

Class 7 land on Windblown Sands

The unstable belt of recent windblown sands along the coast has been mapped as Class 7

land because of the extreme erosion hazard (both present and potential).  These areas

comprise the foredune and adjacent unstable sand dunes and sand plains (refer to Figure

10).  These dunes are the most exposed and have very little or no soil development.  This

together with the rolling nature of the dunes gives them the potential for extreme wind

erosion.  Where exposed, the sand is easily transported by wind, with extensive areas of

blow out dunes and wind eroded areas present.  Revegetation is crucial in order to stabilise

the dunes and prevent migration of sand onto productive farmland.

The areas of Class 7 land on coastal windblown sand generally occur as a narrow strip up

to approximately 0.25 km wide, along the coastline.  At Five Mile Bluff the area is more

extensive, extending up to 1.5 km inland.

Class 7 land on coastal sand dunes has been mapped at Northdown Beach, and from Low

Head to east of Beechford.

Soils mapped are the Kelso Association (Beaconsfield Soil Survey; Dimmock,

unpublished), which is a weakly podzolised calcareous sand, with very weak soil profile

development.

Class 7 land on sandstones, slates and quartzites

This type of Class 7 land occurs on extremely steep slopes on Precambrian age sediments.

These rocks are very hard and highly siliceous, and form the backbone of the Asbestos and

Dazzler Ranges.  The areas of Class 7 mapped on this type of land occur south of Badger

Head, and at Flowers Hill (west of York Town).

Slopes are generally very long and steep (over 45%).  Soils can be quite stony with angular

fragments of quartzite throughout the profile and over the soil surface.  The Asbestos Soil

Association has been mapped on this type of land in the Beaconsfield Soil Survey

(Dimmock, unpublished).

The extremely steep slopes and potential erosion hazard make this land unsuitable for

agricultural use.

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*Soil Association names from Beaconsfield Soil Survey (Dimmock, unpublished)

Figure 11:

Cross section of West Tamar area showing landform, geology, soil and land capability relationships

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73

10.8 Summary of Land Capability Classes on Tamar Map

Class

Area

(ha)

%

of land area on

Tamar map

1

42

0.02

2

604

0.33

3

10 061

5052

4

56 953

31.26

5

36 773

20.18

6

26 038

14.3

7

874

0.48

Exclusion

50 084

27.9

TOTAL

182149

100

Table 9: Summary of areas on Tamar map.

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11. Map Availability

An index of the land capability maps (based on the Tasmap 1:100 000 Series) is shown on

the rear cover of this report.

Publications currently available in the series are:-

PIPERS REPORT AND ACCOMPANYING MAP

TAMAR REPORT AND ACCOMPANYING MAP

LAND CAPABILITY HANDBOOK

Flat Maps are also available for purchase.

Maps and reports are available for purchase from your nearest Department of Primary

Industry and Fisheries Office, or can be ordered direct from:

Department of Primary Industry and Fisheries Bookshop

G P O Box 619F

HOBART  TAS  7001

Ph [phone]