Previous PageTable Of ContentsNext Page

Botanical diversity within two saline ecosystems in southwestern Australia

Hayley C. Norman, Robyn A. Dynes and David G. Masters

CSIRO Livestock Industries, Private Bag 5, Wembley, WA 6913, Australia. Hayley.Norman@csiro.au

Abstract

Species composition within two typical saline paddocks in southwestern Australia was assessed in the spring and autumn. Plant diversity within the paddocks was much higher than the diversity that is often found in non-saline pastures in these areas. The Meckering paddock contained 31 plant species, and the Tammin paddock contained 24 plant species. It is expected that high levels of plant diversity within paddocks are maintained by niche differentiation; i.e. no one species can dominate in all of the functional niches within the paddock. In light of the inherent variation within saline areas, it is unlikely that monocultures of sown species will be optimal when revegetating saline land.

Key Words

Salinity, halophyte, ecology, saltbush.

Introduction

In southwestern Australia, 10 % or 1.8 million ha of the farmed area is affected by dryland salinity and a further 6 million ha are threatened (1). One option for farmers is to plant salt-tolerant grasses, trees and shrubs in saline areas. These plants improve the visual amenity of saline land, provide feed for livestock, may reduce the spread of salinity and probably increase the biodiversity value of saline land. However, vegetation on saline land tends to remain patchy and there are few planting options available to farmers. The aim of this study was to assess botanical diversity within two paddocks that were once cropped and were subsequently sown with salt-tolerant species in the early 1980’s after becoming saline. It was predicted that botanical diversity would be low due to salinity, waterlogging and past farming practice.

Methods

The paddocks that were studied in 2001 are situated near Meckering (130 km east of Perth) and Tammin (180 km east of Perth). Soil samples were collected across paddocks in March 2001 to measure electrical conductivity and peizometers were used to monitor the water table. Botanical composition was assessed in autumn and spring using the dry-weight rank method of Mannetje and Haydock (2). Briefly, the paddocks were crossed by five transects in both autumn and spring, with botanical assessments made every 15 m along transects. For each assessment, the three herbaceous plant species that appeared to contribute most biomass were ranked in descending order from 1-3. Rankings were totalled and multiplied by a weighting factor to give a percentage of biomass/species.

Results

The Meckering paddock (19 ha) was the more saline and waterlogged site as 20% of the area had become a bare salt scald. On average the soil was highly saline (ECe 48 dSm-1) and the saline water table (ECw 27 dSm-1) was 66 cm below the soil surface in March. The soils in the Tammin paddock (12 ha) were on average highly saline (ECe 25 dSm-1) and the groundwater (164 cm below the soil surface in March) was highly saline (ECw 56 dSm-1). The topography of both paddocks was undulating.

Table 1 summarises the results. The Meckering paddock contained 31 herbaceous plant species, of which five were sown (early 1980’s) and 26 were volunteers. Only 23 % of the species were native to Australia. The most common species at the site in autumn were the grass Puccinellia ciliata and the halophytes Atriplex undulata, A. lentiformis, A. semibaccata and Halosarcia spp. In spring, the annual herbs Mesembryanthemum nodiflorum and Cotula coronopifolia formed 16.5 % of the botanical composition. The Tammin paddock contained 24 plant species of which five were sown and 19 had volunteered. One third of the recorded species were native to Australia. The most common species were Maireana brevifolia, Halosarcia spp. and Lolium rigidum.

Table 1. Botanical composition (%) in autumn and spring of two salt-affected paddocks.

Species

Common name

Status

Origin

Tammin

Meckering

       

autumn

spring

autumn

spring

Halophytes

Atriplex amnicola

river saltbush

sown

Australia }

   

2.7

< 1.0

Atriplex nummularia

oldman saltbush

sown

Australia }

6.9

4.1

-

-

Atriplex semibaccata

creeping saltbush

sown

Australia }

   

4.2

1.0

Atriplex undulata

wavy-leaf saltbush

sown

Argentina }

   

19.2

6.5

Atriplex lentiformis

Quailbrush

sown

USA

-

-

6.1

7.5

Haloscaria spp.

Samphire

volunteer

Australia

21.2

27.9

9.5

8.4

Maireana brevifolia

small-leaved bluebush

volunteer

Australia

32.1

20.4

1.5

2.3

Grasses

Avena fatua

wild oat

volunteer

Mediterranean

< 1.0

< 1.0

< 1.0

< 1.0

Chloris virgata

windmill grass

sown

Australia

< 1.0

< 1.0

-

-

Eragostis curvula

African lovegrass

volunteer

South Africa

-

-

< 1.0

< 1.0

Eragostis dielsii

prostrate lovegrass

volunteer

Australia

10.5

3.6

7.1

3.3

Hordeum leporinum

barley grass

volunteer

Mediterranean

< 1.0

< 1.0

< 1.0

< 1.0

Hordeum marinum

sea barley grass

volunteer

Southern Europe

8.8

3.9

2.3

3.7

Lolium rigidum

annual ryegrass

volunteer

Mediterranean

8.3

17.7

6.4

3.5

Parapholis incurva

coast barbgrass

volunteer

Mediterranean

< 1.0

< 1.0

-

-

Paspalum vaginatum

saltwater couch

volunteer

America

< 1.0

< 1.0

1.1

< 1.0

Puccinellia ciliata

Puccinellia

sown

Turkey

-

-

34.0

30.8

Vulpia spp.

silver grass

volunteer

Mediterranean

10

2.8

< 1.0

3.4

Other

Arctotheca calendula

Capeweed

volunteer

South Africa

< 1.0

< 1.0

< 1.0

3.6

Conyza spp.

Fleabane

volunteer

America

-

-

< 1.0

< 1.0

Cotula coronopifolia

Cotula

volunteer

Australia

< 1.0

9.7

< 1.0

7.7

Heliotropium curassavicum

Heliotrope

volunteer

cosmopolitan

-

-

< 1.0

< 1.0

Hypochaeris radicata

Flatweed

volunteer

Europe

< 1.0

3.4

< 1.0

< 1.0

Juncus bufonius

Toadrush

volunteer

cosmopolitan

< 1.0

< 1.0

< 1.0

< 1.0

Juncus acutus

sharp rush

volunteer

Europe

-

-

< 1.0

2.7

Mesembryanthemum nodiflorum

Iceplant

volunteer

South Africa

-

-

< 1.0

8.6

Plantago coronopus

Buckshorn plaintain

volunteer

Europe

-

-

< 1.0

< 1.0

Ploygonum aviculare

wire weed

volunteer

Europe

-

-

< 1.0

< 1.0

Ptilotus polystachyus

mulla mulla

volunteer

Australia

-

-

< 1.0

< 1.0

Romulea rosea

onion grass

volunteer

South Africa

-

-

< 1.0

3.8

Rumex acetosella

Sorrel

volunteer

Europe & Asia

< 1.0

< 1.0

-

-

Trifolium arvense

haresfoot clover

volunteer

Mediterranean

< 1.0

< 1.0

1.9

< 1.0

Trifolium glomeratum

cluster clover

volunteer

Mediterranean

< 1.0

< 1.0

< 1.0

< 1.0

Trifolium subterraneum

Subterranean clover

volunteer

Mediterranean

< 1.0

< 1.0

< 1.0

< 1.0

Trifolium tomentosum

woolly clover

volunteer

Mediterranean

< 1.0

< 1.0

< 1.0

< 1.0

Conclusion

Plant diversity within the paddocks was as high or higher than the diversity generally found in non-saline pastures in the same areas. The presence of so many species suggests that there is either little competitive exclusion, little agronomic exclusion or the paddocks are divided into botanical niches. It is likely that high levels of plant diversity within paddocks are maintained by niche differentiation; i.e. no one species can dominate (or perhaps even survive) in all of the functional niches within the paddock. The suggestion of niche differentiation was supported by successional changes in species composition across salinity and waterlogging gradients at both sites (data not presented). This diversity should be considered when evaluating options for revegetating saline land.

References

National Land and Water Resources Audit. 2001. Australian Dryland Salinity. Canberra.

Mannetje L.‘t and Haydock, K. P. 1963. J. Brit. Grassl. Soc., 18: 268-275.

Previous PageTop Of PageNext Page