State of the Environment

2006

Indicator: LD-20 Total grazing pressure relative to net primary productivity

Data

An interpretation of livestock density and net primary productivity

An interpretation of livestock density and net primary productivity

Source: Bureau of Rural Sciences 2005, Interpretation of livestock density and net primary productivity, unpub. Data.

Spatial data on livestock density has been intersected with remote sensing data on biomass to show the intensity of grazing pressure across the continent.

The analysis uses spatial data on livestock densities from Agstats 2001, measured as Dry (non-lactating) Sheep Equivalents (DSE ), intersected with spatial data on Net Primary Productivity (NPP), or biomass. The NPP measurement uses MODIS imagery, averaging the Normalized Difference Vegetation Index (NDVI) signal over 2001-2003. NPP is measures as tonnes per hectare.

The map shows that:

Further explanatory information link to:

Source: Bureau of Rural Sciences 2005, Interpretation of livestock density and net primary productivity, unpub. Data.

The above map includes only domestic sheep and cattle. It does not include native grazers or naturalized grazer populations. Few data are available on naturalised populations but some data are available on kangaroos. Pople and Grigg (1999) estimated that Australia's kangaroo population that is exposed to commercial exploitation fluctuates between 15 and 35 million animals. Caughley and Grigg in 1983 had estimated a population of 15 million in areas where kangaroos were commercially exploited and an additional 4 million kangaroos living in areas that are not exploited.

Assuming that, in a good season, the number of kangaroos living in areas where exploitation does not take place reproduce at the same rate and by the same proportion as kangaroos living in exploited areas, this would imply that the non-exploited population would fluctuate between about 4 million and 7 million, This then means that the total national kangaroo population fluctuates between 19 and 42 million.

The DSE of a kangaroo is estimated to be somewhere between 0.2 and 0.7 of a non-lactating sheep. This, at the lowest estimate of both population and DSE, puts kangaroo DSE at about 3.8 million DSE up to a highest estimate of 29.4 million DSE.

The national beef cattle herd is about 28 million and the sheep herd about 101 million in 2005. Using the assumption that beef cattle have a DSE of 8, as used in the BRS analysis above, this gives a total cattle and sheep DSE of 324 million.

This puts the grazing pressure of the national kangaroo herd somewhere between 1% and 8% of national grazing pressure.

The following tables show the following four scenarios:

Domestic and grazing pressure based on non-dairy cattle DSE: 8, maximum kangaroo DSE:0.7, and maximum estimated kangaroo numbers (42 million)
Number (m) Estimated average DSE DSE (m) Percentage of total grazing pressure
Sheep 100 1 100 28%
Cattle 28 8 224 63%
Total Domestic 128 324
Kangaroos 42 0.7 29.4 8%
Total 170 353.4 100%
Domestic and native grazing pressure based on non-dairy cattle DSE: 8, maximum kangaroo DSE:0.7, and minimum estimated kangaroo numbers (19 million)
Number (m) Estimated average DSE DSE (m) Percentage of total grazing pressure
Sheep 100 1 100 30%
Cattle 28 8 224 66%
Total Domestic 128 324
Kangaroos 19 0.7 13.3 4%
Total 147 337.3 100%
Domestic and native grazing pressure based on non-dairy cattle DSE: 8, minimum kangaroo DSE:0.2, and maximum estimated kangaroo numbers (42 million)
Number (m) Estimated average DSE DSE (m) Percentage of total grazing pressure
Sheep 100 1 100 30%
Cattle 28 8 224 67%
Total Domestic 128 324
Kangaroos 42 0.2 8.4 3%
Total 170 332.4 1
Domestic and native grazing pressure based on non-dairy cattle DSE:8, minimum kangaroo DSE:0.2, and minimum estimated kangaroo numbers (19 million)
Number (m) Estimated average DSE DSE (m) Percentage of total grazing pressure
Sheep 100 1 100 31%
Cattle 28 8 224 68%
Total Domestic 128 324
Kangaroos 19 0.2 3.8 1%
Total 147 327.8 100%

Sources: Department of the Environment and Heritage (DEH), 2005, derived from:

What the data mean

Areas of low NPP (about 62% of the continent) are at risk from any level of grazing intensity because they are likely to have much less in the way of vegetation protecting the soil from erosion, and will find it more difficult to revegetate if existing biomass is eaten or otherwise cleared or killed.

Areas of low NPP and high DSE (around 20,649 km2) are most at risk.

Total grazing pressure is the combined effect of grazing by all animals. It includes grazing by both introduced and native grazers (including kangaroos and insects and everything in between). However, in terms of numbers, the pressure of introduced grazers - between 92% and 99% of combined grazing pressure is clearly much more significant than the pressure of kangaroos. The highest estimate of kangaroo pressure, referring to the highest estimate of kangaroo numbers, would only occur during periods of very high biomass production, when domestic animal stocking densities are also likely to be higher and when grazing pressure may in fact be less of an issue than fire risk. If the highest DSE estimate for kangaroos is an overestimate, even this level of grazing pressure would not occur.

Aside from DSE, which is a way of comparing only how much vegetation animals consume, not other aspects of their impacts, the impact per animal of native herbivores on the environment is also considerably lower than that of introduced herbivores. Native animals are better adapted to the Australian landscape than introduced grazers. (See also: LD-04 Area and change in area of exposed soil surface contributing to erosion ) Intensity of grazing pressure is also influenced by whether grazer numbers are controlled by human action rather than natural forces.

Data Limitations

Although the grazing pressure map, above, presents a continuous surface for livestock density, the actual distributions and levels may be quite different at the regional or local scale.

Land use, land cover or land management are not taken into account. Forested areas will show up as having high NPP, even though this NPP is not always available to grazing animals.

When converting cattle to sheep equivalents, i.e. DSE, a factor of 8 is assumed; this is not appropriate for diary cattle which are generally clustered around high rainfall coastal areas.

The NPP was calculated for a longer time frame that was after the period covered by the ABS livestock census and covered a period of severe drought in eastern Australia that may alter the boundaries between the categories.

Numbers of wild grazers may have been modified by human land use or other activities, and are therefore relevant to this indicator, but the ABS data used for the spatial analysis does not include them, or anything else that can consume pasture and contribute to grazing pressure. The above analysis of the proportion of grazing pressure represented by non-domestic animals is a rough application of very limited available data and has no spatial application.

Issues for which this is an indicator and why

Land - Direct pressure of human activities on the land - Species introduction and species change 

Grazing pressure is a complex issue involving the introduction of non-native grazers and non-native pasture, as well as anthropogenic expansion of native pasture and native grazers. It is one of the principal ways in which introduced species can impact on the land.

Grazing removes groundcover and nutrients from the land, often land that has already suffered substantial loss of cover and nutrients through land clearing and loss of associated biodiversity. It exposes the land to further nutrient loss through soil erosion. The loss of soil, soil ecosystems, soil nutrients and pasture biodiversity can preclude vegetation (either natural or agricultural) and other biodiversity from re-establishing.

This indicator measures the pressure of grazing by introduced domestic animals in terms of the biomass available for grazing and therefore gives a broad picture of the area of the continent affected by various degrees of grazing pressure by introduced animals and altered populations of native animals.

Other indicators for this issue:

Land - Direct pressure of human activities on the land - Land clearing 

Although grazing is primarily an issue arising from the pressure of introduction of new species to the land (pasture, in some cases, exotic pasture, replacing native vegetation and introduced animals replacing native animals), overgrazing also has the potential to completely remove ground cover, leaving bare soil. The indicator gives a spatial indication of where this is most likely to happen.

Other indicators for this issue:

Biodiversity - Pressures on biodiversity - Grazing pressure 

Grazing by introduced herbivores can cause widespread damage through trampling and of fouling waterholes, selective indiscriminate or close grazing of vegetation, spreading weeds and trampling the home sites of ground-dwelling animals. Reduction in groundcover in turn exposes bare soil to erosion.

The quality of the mid-storey and understorey of forest and woodland ecosystems can be significantly modified as a result of grazing by livestock, or clearing for grazing, and simplification of these ecosystems can lead to a decline in species and genetic variability. In general, as grazing pressure increases, the total number of resident species is reduced, reducing the overall diversity and resilience of the ecosystem.

This indicator measures the pressure of grazing by introduced domestic animals in terms of the biomass available for grazing and therefore gives a broad picture of the area of the continent affected by various degrees of grazing pressure. Areas of high biomass tend to be more diverse, so the indicator gives an indication of areas where the most biodiversity is at risk from grazing, but it also gives an indication of low biomass areas under pressure from grazing where much more fragile remnant biodiversity may be at risk.

Other indicators for this issue:

Biodiversity - Pressures on biodiversity - Invasive species 

While the term “invasive” is usually used to refer to introduced species of plant and animal that have become naturalised in the wild, in terms of scale of impact, the invasive impact of introduced plants and animals utilised in agriculture, and especially introduced grazing animals and introduced pasture for them to graze on, is much more significant.

Other indicators for this issue:

Further Information

For more information on the NDVI, see :

Key

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   Links to data in the DRS
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