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Native and Improved Grasslands

Native grasslands are terrestrial ecosystems where there are few or no trees present naturally and the grassy understorey species are native to SEQ. Improved grasslands are those ecosystems where the tree canopy has largely been removed; the resultant grassland is often  comprised predominantly of exotic species of grass but also may be dominated by native grass species. Grasses are the dominant species in these ecosystems and comprise a high proportion of the total biomass.

 

MILLENNIUM ECOSYSTEM ASSESSMENT REPORTING CATEGORY

Dryland Ecosystems

 

What ecosystem functions do native and improved grasslands perform?

Kangaroos and wallabies benefit from grasslands, as do commercial species such as sheep and cattle.

There are comparatively only small areas of native grassland in the SEQ Bioregion but substantial areas of 'improved' grassland derived through removal of trees. The tree layer, depending on rainfall (700-1900 mm per annum) and soils, would previously have been rainforest, or wet or dry schlerophyll forest or woodland. Relative to other ecosystems in SEQ, native and improved grasslands contribute to many ecosystem functions important to the provision of ecosystem services (see Table 1).

In SEQ, native and improved grasslands provide good soil retention capacity due to their fibrous root systems. Maintaining a grassy land cover also minimises soil loss through buffering the impacts of water (rain and flooding) and reducing the soil's exposure to wind. These soil retentive properties are particularly important on hillsides, slopes and streambanks where the gravitational pull adds pressure on soils to destabilise their structure.

Grassland ecosystems are important for performing the function of soil formation as dead organic matter becomes recycled through the ecosystem, building soil structure and helping to improve the productivity of soils. Native and improved grasslands store plant nutrients above and below ground, rapidly recycling nutrients through death and decay of foliage, grazing by herbivores (including insects) and return of nutrients to the soil via manure. Leguminous components fix atmospheric nitrogen through a symbiotic process, enhancing soil fertility. Organic matter in the soil, derived through photosynthesis, aids nutrient retention.

Grasslands with a high proportion of native species comprise complex ecosystems with numerous herbaceous species which provide habitat for a wealth of micro-organisms (e.g. soil biota), invertebrate (e.g. insects) and small vertebrate species (e.g. birds and reptiles). Both invertebrates and vertebrates are important for the regeneration of grassland (and other) ecosystems as they act as pollinators and influence species balance by selective grazing. Various macropods (e.g. kangaroos, wallabies) benefit from both classes of grassland. Because improved grasslands are important ecosystems for the grazing of species such as sheep and cattle, they indirectly provide a major source of food for humans in the form of edible protein (e.g. milk, beef and lamb). Grasslands also provide food for horses.

 

Table 1:The relative magnitude (to other Ecosystem Reporting Categories) native and improved grasslands perform each ecosystem function.

Ecosystem Function Category Ecosystem Function 0
1
2
3
4
5
Regulating Functions
Gas Regulation            
Climate Regulation            
Disturbance Regulation            
Water Regulation            
Soil Retention            
Nutrient Regulation            
Waste Treatment and Assimilation            
Pollination            
Biological Control            
Barrier Effect of Vegetation            
Supporting Functions
Supporting Habitats            
Soil Formation            
Provisioning Functions
Food            
Raw Materials            
Water Supply            
Genetic Resources            
Provision of Shade and Shelter            
Pharmacological Resources            
Cultural Functions
Landscape Opportunity            
 

What types of native and improved grasslands are in SEQ?

For assessment purposes, this Ecosystem Reporting Category contains the following native grasslands - Regional Ecosystems: 12.8.15, 12.8.27. It should be noted that some grasslands, such as those associated with coastal dunes, are included in other Categories due to functional differences.

In improved grasslands, predominant use is large mammal herbivory (i.e. grazing). Sown grass species are predominantly Rhodes grass (Chloris gayana), setaria (Setaria sphacelata), Kikuyu grass (Pennisetum clandestinum) and green panic/Guinea grass (Megathyrsus maximus). Sown legumes include lotononis (Lotononis bainesii) glycine (Neonotonia wightii), siratro (Macroptilium atropurpureum) and desmodium (Desmodium spp.). Some ryegrass and clover is sown for irrigated winter pastures.

 

What is the area and extent of native and improved grasslands in SEQ?

 

A large proportion of grasslands are managed by private landholders particularly for grazing purposes.

Links to other publications and websites

Native Grass Identification
Managing Native Grasslands
Carbon Sequestration Opportunities
Econ. Analysis of Grasslands
World Grasslands and Biodiversity

Native and improved grassland areas cover 10 010 km2, 39.84% of SEQ. This map shows grassland ecosystems cover the bulk of the SEQ landscape, mostly found in the western parts of the SEQ region. The majority of the grasslands identified in this map are 'improved' grasslands. In the eastern, higher rainfall part of the region substantial clearing of rainforest has been carried out and the land planted to Kikuyu grass (a perennial ground-hugging grass often used for pastures, lawns and playing fields). However small remnants of native grasslands can be found on steep slopes  in the Bunya Mountains.

 

What is the vulnerability of native and improved grasslands and threats to this ecosystem in SEQ?

This ecosystem is vulnerable to high variations in annual rainfall. This variation is likely to increase in response to climate change identifying possible future pressures on grassland ecosystems. Selective grazing causes changes in the balance of species within the system which may be irreversible. Changes in soil fertility over time result in changes in species composition.

Primary threats to grassland ecosystems include progressive urbanisation; invasion by unpalatable exotic grasses (e.g. giant rat’s tail, Sporobolus spp.) and shrubs (e.g. lantana); overgrazing (e.g. exposure of soil surface to erosion, soil compaction); reduced soil fertility; and in the case of coastal ecosystems over use through recreation and tourism activities. Native grassland ecosystems are also subject to change through invasion by ‘improved’ pasture grasses, with a resultant loss in biodiversity.  Fire may change the level of biodiversity in grasslands, often promoting the increased dominance of exotic species, and also adversely affects rainforest/grassland margins.

 

How do we manage native and improved grasslands in SEQ?

A large proportion of improved grasslands in SEQ are managed by private landholders, particularly for grazing purposes. Other areas are public land, such as conservation areas and National Parks and roadsides. The native grassland area 12.8.15 is largely protected in a National Park, though it is subject to forest encroachment and weed invasion. The other area of native grassland 12.8.27, is threatened by urban development. It is in both the Landholder's and community’s interest for grasslands to be managed for their longer term private and public benefits. However, this may not always achieve the best long-term ecological outcomes as high productivity of grasslands is not associated with biological diversity. Guidelines for pasture management are available through the Queensland Department of Agriculture Fisheries and Forestry.

Future grassland management should be directed towards balancing grazing pressure against pasture on offer, in order to achieve long-term sustainability. However, high livestock production is not necessarily compatible with high biological diversity.