Vegetation and flora of a diverse upland remnant of the Western Australian wheatbelt



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19

Vegetation and flora of a diverse upland remnant of the Western Australian

wheatbelt (Nature Reserve A21064).

F J Obbens

1

 & L W Sage



2

1 C/o Western Australian Herbarium, Department of Conservation and Land Management

Locked Bag 104, Bentley Delivery Centre WA 6983

 bushtech@wa1.quik.com.au

2 Swan Coastal District, Department of Conservation and Land Management,

5 Dundebar Road, Wanneroo WA 6065

 leighs@calm.wa.gov.au

Abstract

In the Western Australian wheatbelt, small intact remnants of bushland can contribute

significantly to overall biodiversity. Our comprehensive vascular flora survey of Nature Reserve

A21064, a reserve of 110 hectares near the town of Arthur River, has highlighted this aspect.

Comprehensive surveys of selective wheatbelt reserves provide benchmarks to help us better

understand the flora and vegetation in this highly cleared and fragmented agricultural landscape.

In the diverse flora of this relatively undisturbed upland remnant ten distinct plant communities

encompassing heaths, herbfields, mallee and woodlands can be recognised. The survey identified

323 vascular plant taxa including one rare species, seven priority species and a number of taxa of

special interest recorded from 51 families. Weeds accounted for 22 species (6.8% of total flora),

however, the extent of invasion is relatively low.

Keywords:

 Vegetation and flora survey, upland remnant, biodiversity, wheatbelt woodlands



(Manuscript received January 2003; accepted December 2003)

Journal of the Royal Society of Western Australia, 87:19–28, 2004



Introduction

Nature Reserve A21064 is an upland bush remnant of

high conservation value (i.e. “A” class nature reserve)

with a diverse flora (see species list in Appendix 1). It is

approximately 110 ha in area and is located about 190 km

directly south-east of Perth near the town of Arthur

River, Western Australia (Fig 1). The district has a dry

Mediterranean type climate with very warm, dry

summers and cool, wet winters. Average annual rainfall

for the reserve is about 470 mm, which is typical of the

wetter western (inner) margins of the wheatbelt.

The reserve is situated at the end of an eroded and

generally flattened ridgeline and its upper slopes; the

ridge is the watershed between Mailling Gully to the

south and a smaller unnamed tributary to the north.

These streams eventually drain into the Arthur River

about 7 km west of the reserve. The Arthur River and

adjacent Norcott Plains also run north of the reserve,

about 3 km away. The reserve is a small L-shaped

remnant with the longest east-west boundary (1.9 km)

roughly parallel to the ridgeline/plateau. The north-

south arm of the L measures approximately 1.2 km (Fig

2). Slopes descend gently off the ridgeline and the

predominant aspect is north or north-west. A pattern of

low undulating hills/ridges with interspersed small

valleys and/or plains is typical locally and is a familiar

topography for much of this inner wheatbelt region.

Granite outcrops and/or lateritic breakaways are often

found on the upper slopes or hilltops. Historically, many

upland areas were not cleared for cropping because of

the rougher topography. Also upland areas were

generally abundant in the poisonous Gastrolobium species

that killed domestic stock. Alternatively, some were left

as ‘shade and shelter belts’. Today, very few of these

upland remnants have survived completely intact.

Significant numbers have had a reduction in tree cover

due to past logging (e.g. for timber and fence posts),

insect pests, disease etc, and this has occurred in a

© Royal Society of Western Australia 2004

Figure 1

. Location of A21064 Nature Reserve, near Arthur River,

in the south-west of Western Australia; also shown are 100 mm

rainfall isohyets.



20

Journal of the Royal Society of Western Australia, 87(1), March 2004

relatively short time frame (Landsberg et al. 1990). The

majority of these remnants are also depauperate in

understorey taxa due to selective clearing (e.g. of ‘poison

plants’), frequent grazing by domestic stock, changed

burning regimes, nutrient enrichment, weed invasion,

and other human influenced disturbances (Hobbs &

Atkins 1988; Hobbs 1993; Panetta & Hopkins 1991; Pigott

1994; Yates & Hobbs 1997; Yates et al. 1999; Yates et al.

2000).

The wheatbelt region as a whole has been altered from



a mosaic of perennial native vegetation to predominantly

cleared agricultural land with fragmented small

bushland remnants (Hobbs 1998; Scanlan et al. 1992).

A21064, which is surrounded by agricultural land, is no

different. Beard (1980a) mapped the pre-existing

vegetation cover of this entire region using aerial

photography in conjunction with a wide-ranging

examination of the remaining bushland remnants and

their preferred habitat requirements (i.e. soil, slope,

aspect, evelation etc). These vegetation maps show the

reserve’s wider surrounding district as predominantly

York gum (Eucalyptus loxophleba) and wandoo (E. wandoo)

woodland, while several local upland areas (including

A21064) are mapped as wandoo and mallet (Eucalyptus



astringens) woodland. This is a reasonably accurate

representation, although these upland areas also contain

significant patches of sheoak (Allocasuarina huegeliana).

Approximately 20-25 km west of the reserve, wandoo

woodland predominates, but marri (Corymbia calophylla)

and jarrah (Eucalyptus marginata) become more common

about another 20 km further westwards within Hillman

and Godfrey State Forest Blocks (Smith 1974). Powder

bark wandoo (E. accedens) is more abundant amongst the

York gums around the Narrogin area, about 35 km north

of the reserve (Beard 1980b). Salmon gum (E.

salmonophloia) tends to replace wandoo further east (25-35

km), while the Beaufort River area, about 30 km south of

the reserve, has a mix of wandoo, yate (E. occidentalis),

teatree (Melaleuca sp.), Casuarina obesa and samphire flats

(Beard 1980a). Overall, the district was once dominated

by open woodlands; however, patches of heath (often



Dryandra dominated), herbfield and mallee were also

relatively common.

Flora surveys of wheatbelt remnants are sparse

(Obbens et al. 2001). Although not intensive, Muir’s

(1977a) pioneering surveys of 24 wheatbelt reserves are a

notable exception. There are very few flora surveys of

remnants from around this district, reflecting the high

costs of surveying remnants within this vast wheatbelt

region (i.e. 18 million hectares). The soon to be released

Salinity Action Plan (SAP) surveys will change this

situation. While larger remnants (i.e. >2000 ha) are

certainly important for conserving biodiversity and

helping to maintain many of the ecological processes of

this region, this paper aims to highlight the important

contribution of smaller remnants to regional biodiversity,

particularly if they remain intact. A further aim is to

present more botanical survey data for this significant

region.


Methods

The vegetation communities of Nature Reserve

A21064 were interpreted from a 1996 aerial photograph

and confirmed in the field during 1999 and 2002.

Classification of these vegetation communities is based

on Muir (1977b). This classification assesses vegetation

structure by taking measures of lifeform/height class and

canopy cover/density class to produce a vegetation type.

For example, trees 15-30 m with a 10-30% canopy cover

were designated woodlands, while the same trees with a

canopy cover of 2-10% would be designated as open

woodlands. To a significant extent this classification also

reflects the species compositional differences.

Additionally, brief investigations were made of the soils

in each vegetation community. The soil surface was

inspected and then shallow holes (3-5 cm depth) were

made to assess soil texture and colour.

The flora survey and collections were accomplished

by walking along 13 transects (10 spaced at 150 m apart

and 3 spaced at 100 m apart) that spanned the full width

of the reserve in a north-south orientation. The first

transect proceeded in a southerly direction from Noble

Road and approximately 50 m in from the reserve’s

north-east corner. Subsequent transects crossed every

vegetation type several times using this technique. This

transect survey was undertaken during mid/late spring

(i.e. October and November 1998). An additional 8

surveys were also carried out between the summer of

1998 and the spring of 2002. On these occasions a

‘randomized stratified walk’ technique (Hopper et al.

1997) was used. This method involves specimen

collections via random walks in each vegetation

community. The purpose of this intensive surveying was

to obtain a voucher specimen of each taxa and to compile

a more complete vascular flora list.

All specimens were submitted for incorporation at the

WA Herbarium. The species names follow the currently

accepted botanical binomials of WACENSUS (WA

Herbarium census of Western Australian vascular

plants), while conservation status of species is according

to the Department of Conservation and Land

Management’s (CALM) Declared Rare Flora and Priority

Flora list (Atkins 2001). The authors also received

invaluable information from WA Herbarium database

records (WAHERB and FLORABASE). The term “total

‘Liliaceae’” refers to the number of closely related, but

different new families that have been split from Liliaceae

in recent years. For A21064 this includes the families

Anthericaceae, Boryaceae and Phormiaceae.

Results

Vegetation and habitat.

Interpretation of the aerial photograph and site survey

indicated ten major vegetation communities (Fig 2),

including four variants (all explained below). However,

there is considerable variability within some

communities and at differing locations throughout the

reserve. Additionally, there was a range of community

boundaries, some very distinct (e.g. between pure mallet

stands and wandoo woodland or when pure

Allocasuarina huegeliana stands surround granite-exposed

herbfield areas). However, diffuse boundaries have been

drawn at roughly midpoint where any two communities

overlapped (e.g. as demonstrated when Low Woodland

and Low Forest communities merge).


21

1

 Open Woodland. Dominated by Eucalyptus wandoo with

a generally very open, but variable understorey. This

includes areas of almost pure Gastrolobium trilobum or



Melaleuca aff uncinata or ‘parkland-like’ areas with

numerous orchids/annuals/grasses and smaller shrubs.

Many trees are large to 25 m high with a canopy density

about 5 – 15% (i.e. very sparse to sparse). Soils are either

grey coarse sandy loams or, at the reserve’s western end,

brown coarse loams with some lateritic gravels. This

community represents the top end of shallow drainage

lines that form defined creeks further down slope outside

the reserve boundaries.

1a

 Open Woodland. A variant of above, again, dominated

by Eucalyptus wandoo of generally smaller stature and with

a denser canopy cover, about 10 – 25% (i.e. sparse). Lying

entirely on lateritic ridge country, it demarcates itself from

community 1 along the line of a small breakaway. A

sparse to mid dense understorey of predominately

Dryandra species occur on exposed lateritic boulders with

residual soils on the top edge of the breakaway and up

slope at the ridgeline. Elsewhere is fairly open with

various scattered shrubs and some annuals on soils of red-

brown clay loam with numerous gravels.

2

 Low Woodland. A mixed woodland with a mid dense

canopy cover (i.e. about 30 – 70%) consisting of almost

equal proportions of Eucalyptus wandoo (up to 20 m high)

and Allocasuarina huegeliana on grey-brown sandy loams

sometimes with varying amounts of gravel. Understorey

is variable including open areas of low shrubs, annuals

and some grasses to mid dense areas of Acacia or



Gastrolobium.

2a

 Low Woodland. A mixed woodland variant of above

with mid dense canopy consisting of Eucalyptus wandoo

(up to 20 m high) and interspersed individuals or patches

of  Eucalyptus astringens subsp astringens (Brown Mallet)

and occasionally with scattered Allocasuarina huegeliana.

Again, a variable understorey ranging mostly open to

mid dense in parts. Soils are red-brown coarse clay loams

with gravels and sometimes there is exposed lateritic

hardcap.


3

 Low Forest. Predominantly pure stands of Allocasuarina



huegeliana with occasional scattered Eucalyptus wandoo

and generally mid dense to dense canopy cover (i.e.  >

70%). Soils are grey-brown to red-brown sandy or clayey

sand loams sometimes with a little gravel. The

understorey canopy cover is open to mid dense,

including numerous annuals and commonly a tall



Lepidosperma sp (FO204/98), Agrostocrinum scabrum and

Hypocalymma angustifolium. This community occurs

where granite is close to the surface and often

outcropping or boulder stacks are nearby.

4

 Woodland. Composed of pure stands of tall (i.e. 25 – 30

m) Eucalyptus longicornis with a very sparse understorey

of  Acacia erinaceaAcacia lasiocarpa var. sedifolia, a few

sedges and annuals found on red-brown clay loams.

These areas appear to be associated with shallow

drainage zones.

5

  Heath. A heath of mid dense to dense canopy cover

containing a diverse mix of shrubs about 1 – 2 m high on

grey-brown sandy clay loams with some gravel content.

The families Myrtaceae, Proteaceae, Goodeniaceae,

Papilionaceae and Stylidiaceae are well represented along

with many others. This community occurs on the gentle

mid slope areas of the reserve and never appears on the

ridge top.

5a

  Heath. A variant of the above comprising a diverse

mix of shrubs (about 1 – 2 m) with interspersed emergent

shrubs (to about 3.5 m) namely Dryandra sessilis and



Nuytsia floribunda. This unusual combination occurs on a

localised sheet of white sand, which probably overlays

lateritic and/or granitic profiles seen adjacent to this

community. Eremaea pauciflora dominates although many

other species are present.

6

  Low Heath. A very diverse mix of small to mid sized

shrubs (about 0.25 – 1.5 m) with a mid dense canopy

cover found on white-grey clayey loams with occasional

gravel content. This soil profile is possibly exposed and

eroding kaolin, and occurs extensively on lower parts of

the flattened ridgeline. This community contains the

same families as outlined for community 5; however, it

also has a marginally greater diversity of taxa than the

above heaths.



Figure 2

. Map of vegetation communities of A21064 Nature Reserve that include 1 and 1a Open Woodland, 2 and 2a Low Woodland, 3

Low Forest, 4 Woodland, 5 and 5a Heath, 6 Low Heath, 7 Thicket (Tall Heath), 8 Herbfield, 9 and 9a Mallet Woodland, 10 Mallee

Woodland and G Rehabilitated gravel pits. Communities are described below.

Obbens & Sage: Vegetation and flora of an upland remnant, Western Australian wheatbelt


22

Journal of the Royal Society of Western Australia, 87(1), March 2004



7

 Thicket (Tall Heath). Comprising a dense mix of taller

shrubs (about 1.5 – 3.0 m) dominated by Dryandra,

particularly D. armata and D. nobilis, but including some

other tall Proteaceae species (e.g. Adenanthos cygnorum

and Hakea trifurcata) and occasionally interspersed

mallees. These thickets are located on the flattened

ridgeline. The soils are red-brown to grey-brown coarse

clayey loams or sandy loams with abundant lateritic

gravels, rocks and some exposed hardcap.



8

 Herbfield. Exposed or near-surface granite sheets with

some residual surface soil or soil pockets frequently

covered by Borya sphaerocephala, mosses and lichens, but

including numerous annual herbs and some sedges.

Generally abutting or surrounded by Allocasuarina

woodland.

9

 Mallet Woodland. Dense pure stands of Eucalyptus



astringens subsp astringens (about 10 to 20 m) with an

almost absent understorey except for a few resilient

shrubs and abundant bark litter. Soils are red-brown to

brown coarse clay loams with numerous gravels. All

occurrences in the reserve are on the ridgeline including

one area adjacent to and on a lateritic breakaway slope.



9a

 Mallet Woodland. This community, a variant of the

above, comprises more open and generally taller (about

15 to 25 m) stands of Eucalyptus astringens subsp



astringens often interspersed with E. wandoo or

Allocasuarina huegeliana and with variable canopy cover

ranging from open to mid dense. The open to mid dense

understorey includes Acacia celastrifoliaA. pulchella,

Nemcia obovataDryandra nobilis and many others. Soils

are red-brown to grey-brown clayey loams containing

numerous gravels with rocks/hardcap regularly

occurring within this ridgeline community.



10

  Mallee Woodland. Consisting of various mallee

species, but occasionally pure stands to 4 m high and

sometimes with other tree species interspersed or with

tall shrubs. In the western end of the reserve these

mallees tend to be Eucalyptus aspersaE. falcataE. latens

and  E. thamnoides subsp megista while in other areas

mainly E. incrassata and E. pluricaulis subsp pluricaulis.

This community is located either on the ridge or the

adjacent upper slope areas where the soils are red-brown

loams with gravels. .

G

  Rehabilitated gravel pits. Old gravel extraction sites

that have been deep ripped and allowed to regenerate

naturally. At this stage, the flora comprises mainly

pioneer species and limited occurrences of several weed

species.


Flora.

A total of 323 vascular plant taxa (including 22 weed

species) from 51 families was listed for Nature Reserve

A21064 with dicots and shrub species being the

predominant taxa for the reserve (Table 1).

The most represented families were Myrtaceae (39),

Proteaceae (29), Papilionaceae (26), Orchidaceae (26),

Poaceae (20), total ‘Liliaceae’ (20), Asteraceae (17),

Stylidaceae (17), Cyperaceae (16), and Goodeniaceae (12).

Nine Poaceae and three Asteraceae species recorded are

weeds.

The genera with the greatest number of species were



Stylidium (15), Eucalyptus (12), Acacia (10), Caladenia (9),

Hakea (8), Lepidosperma (8), Dryandra (7), Drosera (6) and

Austrostipa,  Leucopogon,  Dampiera,  Goodenia,  Melaleuca,

Daviesia and Petrophile with five species each.

One declared rare species (Conostylis drummondii) and

seven priority species (Dryandra rufistylis, Eucalyptus

aspersa, E. latens, Leucopogon florulentus, L sp

Dongolocking, Microcorys lenticularis and Thysanotus



cymosus) were recorded for the reserve.

Discussion

Vegetation and habitat.

The vegetation of the reserve is not unique because

similar vegetation types or variants thereof can be found

in other upland remnants in this region. Overall the

vegetation of the reserve is relatively pristine and

contains a wide representation of upland communities

for its small size. This alone makes it quite special in

Table 1

Plant type and lifeform for all taxa collected at A21064.



Taxa

Total

Dicotyledons

Monocotyledons

Gymnosperms

Pteridophytes

Families


51

37

12



1

1

Genera



155

98

55



1

1

Taxa:



 (a) native

301


211

88

1



1

 (b) exotic

22

11

11



0

0

Lifeform



Tree

8

8



0

0

0



Mallee/Tree

1

1



0

0

0



Mallee

7

7



0

0

0



Tall shrub

19

18



0

1

0



Low shrub

113


112

1

0



0

Herb (annual)

42

33

9



0

0

Herb (perennial)



127

37

89



0

1

Vine



6

6

0



0

0

TOTAL



323

23

terms of value as public conservation estate. These

woodlands can be moderately diverse due to the

abundant annuals present, but more frequently it is the

open heaths and patches of other communities within

these woodlands that account for the greater proportion

of species diversity, particularly perennial species (Yates

et al. 1999). Table 1 also reaffirms this with 131 perennial

shrub taxa listed, the next highest being perennial herbs

at 127 taxa, but with significantly less vegetative cover

overall than the shrubs produce.




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