Rangelands - Impacts on biophysical resources
Both human activity and natural events have an impact on the biophysical resources of ecosystems. These activities and events include grazing of livestock, and feral and native animals; seasonal events; use of fire; wildfires; introduction of exotic plants and animals; land clearing; and land use.
Climate variability
Rainfall is a major driver of processes and functions in the rangelands (e.g. drought leads to wind erosion, change in animal populations, and land management decisions). Rainfall in Australia's rangelands varies substantially from year to year and from place to place. Understanding this variability and predicting the probability of rainfall is an essential forward looking component of rangelands management.
Rainfall data from point based recording stations can be interpolated mathematically to provide a continental coverage.
Deciles can be used to show how the rainfall received over any period (typically 12, 24 or 36 months) can be compared with historical rainfall records. This gives a better indication of how wet or dry the period has been.
All the rainfalls received over the period of interest are ranked in order from lowest to highest. The lowest 10 percent are in decile range 1, the next 10 percent are in decile range 2, and so on, with the highest 10 percent being in decile range 10.
Map of 12 month deciles
Map of 24 month deciles
Map of 36 month deciles
These images, and a range of other useful information are produced by and available from the Bureau of Meteorology .
Predicting pasture availability
When animal numbers and climate forecasts are combined projected grazing pressure can be calculated and risks of degradation assessed.
The Aussie GRASS (Australian Grassland and Rangeland Assessment by Spatial Simulation) model simulates plant production and provides forecasting of pasture growth, cover and land condition risk. Aussie GRASS is being undertaken through partnership arrangements across participating states.
Aussie GRASS project website for more information
Seasonal characteristics and influence on vegetation
Changes in rangelands need to be interpreted within a seasonal context. The increase in greenness as measured by the Normalised Difference Vegetation Index (NDVI) is an indicator of the effectiveness of the current season compared to past seasons.
List of NDVI information available on this page:
- Seasonal quality as estimated by "greenness" (NDVI)
- Maximum and minimum greenness, and flush greenness
- Seasonal quality, this year so far and previous years
- Number of years since reasonable season
- Number of reasonable seasons since 1991
- Current flush compared to maximum flush
- Other products
Seasonal quality as estimated by "greenness" (NDVI)
Data from weather satellites can be used to estimate the response of vegetation to rainfall, using the Normalised Difference Vegetation Index (NDVI). The NDVI provides an estimate of the vegetation greenness.
NDVI data are compiled every two weeks throughout the year and give continental coverage across Australia. The spatial resolution of the NDVI data is 1 km by 1 km. Each 1 km by 1 km square is called a pixel.
The use of NDVI provides some advantages over rainfall data:
- NDVI can be calculated for each 1km by 1km area of Australia, whereas rainfall data are only available from a limited number of recording stations, which are widely spread in the rangelands.
- NDVI provides an estimate of the response of vegetation to rainfall, whereas rainfall data only provides a measure of the amount of rain that fell.
Rainfall data has the advantage of being composed of a long history of records, in many cases longer than 100 years. However, useful NDVI data are only available from 1991/1992, so that it is more difficult to put the information into historical context.
A range of NDVI products are available from the Environmental Resources Information Network NDVI web site (ERIN).
Maximum and minimum greenness, and flush greenness
As their name suggests, the maximum and minimum greenness images provide estimates of how high and how low the NDVI got within any given year. The difference between the maximum and minimum NDVI within any year is called the flush. Observations show that the flush provides the best estimate of seasonal quality rather than simply using the maximum NDVI.
Maximum greeness for the previous year
Minimum greeness for the previous year
Flush (i.e. max - min) greenness for the previous year
Seasonal quality, this year so far and previous years
The maximum amount that each pixel has flushed so far this year can be compared to the maximum flush recorded since 1991, to provide an idea of how good this year's season has been to date.
The images can either show flush in 10% increments or be categorised for seasonal quality, which provides a more summarised product.
Current year's flush so far compared to maximum flush
Displayed as deciles
Categorised into seasonal quality
The overall seasonal quality for each year is calculated once all the images for that year have been processed and the maximum flush for that year has been observed. Available images display the data either as deciles, or categorised for quality using thresholds.
Maximum flush for 2003, seasonal quality
Displayed as deciles
Categorised into seasonal quality
Images for all years back to 1992, can be found at www.deh.gov.au/erin/ndvi/seasqual.html
Number of years since reasonable season
By looking back at the maximum flush for each year since 1991 it is possible to determine the number of years since each pixel received a "reasonable season".
Typically, a reasonable season is defined as one in which the flush reached more than half the height of the maximum flush recorded. Depending on its use, the definition of "reasonable" can be altered. For example, reasonable can be defined as a season in which the flush reached 60% of the maximum flush recorded and images produced accordingly.
Below are maps which demonstrate number of years since last reasonable season, where ...
Reasonable defined as 50% of the maximum flush recorded
Reasonable defined as 40% of the maximum flush recorded
Reasonable defined as 60% of the maximum flush recorded
Number of reasonable seasons since 1991
By counting how often the maximum flush for each year reached some threshold in relation to the maximum flush recorded since 1991, it is possible to estimate the number of reasonable seasons that have been observed during this period. Typically, a threshold of 50% is set for "reasonable". However, this threshold can be altered (to say 40% or 60%) to suit the needs of the user.
With 50% threshold
With 40% threshold
With 60% threshold
Current flush compared to maximum flush
A comparison can be made between how much flush was recently observed (about 6 weeks after the satellite overpass) and the maximum flush recorded since 1991. This image differs from the previous sets of images in that it shows the recent (close to current) flush, rather than the maximum flush.
Recent flush values compared to maximum flush for the most recent observation
Other products
A range of other NDVI products, including some prototype products that may become useful for assessing change in landscape function over time are available from ERIN's NDVI site.
Total grazing density
Products for total grazing density include historical and current estimates of domestic stock (sheep and cattle), kangaroos and some feral animals (goats and rabbits) and will help understand the pressures on rangeland flora and habitat.
The Audit has collated Australian Bureau of Statistics historical domestic stock information from 1956 to present for statistical local areas and historical and simulated data on macropod and feral animal numbers since the 1950s. Click here to view the data.
Other data collation activities required include data comparison between bioregions, tenure types and the Australian Bureau of Statistics stock information for statistical local areas.
Click on the dates in the tables below to view maps (400-700kb.pdf).
| Animal Density | ||||||
|---|---|---|---|---|---|---|
| Cattle | 1956 | 1966 | 1976 | 1986 | 1996 | 1999 |
| Sheep | 1956 | 1966 | 1976 | 1986 | 1996 | 1999 |
| Kangaroo | 1950s | 1960s | 1970s | 1980s | 1990s | |
| Feral | 1950s | 1960s | 1970s | 1980s | 1990s | |
Total Grazing Density |
||||
|---|---|---|---|---|
| 1950s | 1960s | 1970s | 1980s | 1990s |
Fire -extent, timing and frequency
Fire has shaped much of the vegetation and ecology of the rangelands and is an integral part of rangeland management. The frequency of fires used by Indigenous people to hunt and manage vegetation sometimes changed vegetation types (e.g. open savanna replaced open forest). European settlement and grazing have led to a generally lower frequency of burning and less fuel in the understorey. In semi-arid areas, woody weeds (native and exotic) have become a major problem that requires fire and grazing in their control.
Remote sensing allows managers to view large areas and track fire activity in real time, thus enhancing the ability to manage the effects of fire and assess their impacts over time. The Western Australian Department of Land Administration has been conducting real-time fire monitoring of the Kimberley region since 1993 using NOAA-AVHRR satellite thermal signals from night images. These images provide a 'hot spot' base data for verification with maps of visible burnt areas and ground truthing.
Kimberley Fire Frequency (1993-2000)
Fire hotspots from DOLA (1998-1999)
The NOAA-AVHRR hotspot detection archive shows the individual passes used to make the following 12 monthly map of fire hotspots.
Land use and tenure
An understanding of land tenure and how it has changed over time provides a basis for evaluating the impacts of land use. Land management and administration have been integral to the Australian landscape since its first human occupation.
- Indigenous people managed the land using fire and selective harvesting and developed complex systems for the administration of land through tribal lore and the 'dreaming' (the Indigenous system of beliefs, morals, family and the afterlife).
- The arrival of Europeans saw the development of land management and administration systems that were thought to be the most appropriate at the time but lacked understanding of ecological factors that interplay on the Australian landscape.
Key Audit findings include:
- Land set aside for conservation purposes has increased more than fifteen-fold since the 1950s from 29 100 kmkmē to 441 200 kmkmē (7.8% of the total rangelands area).
- In the 1950s, land reserved for Indigenous use and benefit (covering a variety of titles but not necessarily equating to ownership) was 347 200 kmkmē. In 1999, Indigenous-held land and land reserved for Indigenous use and benefit was 925 200 kmkmē(16% of the total rangelands area and an increase of about 2.5 times).
- Total freehold and leasehold land has remained substantially the same-approximately 57% of the total rangelands area-with nature conservation and Native Title holdings coming principally from 'unallocated' lands.
Land set aside for conservation purposes has increased more than fifteen-fold since the 1950s from 29 100 kmē to 441 200 kmē (7.8% of the total rangelands area).
In the 1950s, land reserved for Indigenous use and benefit (covering a variety of titles but not necessarily equating to ownership) was 347 200 kmē. In 1999, Indigenous-held land and land reserved for Indigenous use and benefit was 925 200 kmē (16% of the total rangelands area and an increase of about 2.5 times).
Total freehold and leasehold land has remained substantially the same-approximately 57% of the total rangelands area-with nature conservation and Native Title holdings coming principally from 'unallocated' lands.
| Summary Table | Area of tenure/use types within rangelands (km2) | |||||
|---|---|---|---|---|---|---|
| Tenure type | 1999 | 1995 | 1985 | 1975 | 1965 | 1955 |
| Conservation | 244,890 | 225,249 | 184,132 | 100,136 | 91,995 | 22,345 |
| State | 58,242 | 58,692 | 60,717 | 68,413 | 72,352 | 72,321 |
| State - no assigned use | 804,179 | 807,471 | 938,081 | 1,103,370 | 1,216,805 | 1,622,352 |
| Defence Reserve | 129,620 | 129,620 | 129,688 | 124,342 | 257,434 | 225,404 |
| Forested | 32,789 | 32,789 | 19,351 | 10,511 | 5,409 | 4,074 |
| Non-indigenous freehold | 525,001 | 525,025 | 532,099 | 538,051 | 538,983 | 539,600 |
| Indigenous leasehold | 159,418 | 152,202 | 46,638 | 55,593 | 1,7043 | 2,754 |
| Reserved for indigenous use | 765,804 | 765,463 | 708,149 | 584,294 | 437,588 | 344,437 |
| Non-indigenous leasehold | 2,661,740 | 2,698,755 | 2,844,090 | 2,931,093 | 2,895,744 | 2,709,209 |
| Marine reserves | 332 | 332 | 253 | 253 | 253 | 253 |
| National parks | 156,966 | 143,402 | 80,159 | 27,891 | 10,514 | 1,397 |
| Other reserve | 2473 | 2454 | 877 | 834 | 786 | 760 |
| Water reserve | 3,760 | 3759 | 980 | 432 | 308 | 308 |
Introduced plants and animals
More than 3000 exotic plants cause billions of dollars worth of damage to Australia's productive capacity and natural resources. Invasive weeds displace native species and their habitats and some are unpalatable or poisonous to livestock.
The National Weeds Strategy is concerned with managing priority weeds that pose threats to primary industries, land management, human and animal welfare, biodiversity and conservation values. It has listed 20 weeds of national significance and a full list is available on the National Weeds Strategy website (www.weeds.org.au). Four species that affect the rangelands are athel pine, mesquite, prickly acacia and parkinsonia.
The maps in this section are products of the Landscape Health project which was undertaken as a partnership between the Audit and the National Reserve System and State of the Environment Reporting sections of Environment Australia. It assesses the ecological condition of landscapes from a biodiversity perspective.
As species level information is generally limited, it used a range of landscape scale condition and trend attributes ie. vegetation extent, fragmentation, and clearing rates, to examine the status of each landscape defined sub-region within Australia?s IBRA bioregions. Assessments involved a combination of quantitative methods supported by national data and more qualitative methods utilising state and territory based expert opinion.
The assessment provides an Australia-wide overview of the relative status of sub-regional landscapes and the significance of key biodiversity threatening processes. A ?landscape stress? classification has also been produced from a synthesis of sub-region condition and trend assessment results.
More on weeds of national significance and introduced animals.
Weeds of national significance that occur n the rangelands
Athel pine grows rapidly and can be very invasive. Athel pine mainly affects riparian areas of central Australia and displaces native vegetation altering the natural habitat. Once established it is difficult and costly to control.
Mesquites are a group of thorny shrubs and trees native to North and South America. They aggressively replace grasslands and shrublands and have the potential to widely affect Australia's pastoral region. Current infestations cover 800 000 ha. Preventing spread is difficult as seed is easily and rapidly dispersed by animals and floodwaters. Plants are also still being planted for shade and land reclamation in remote areas.
Parkinsonia is a thorny shrub native to central America. It was introduced as an ornamental and shade tree around 1900. It is now a major weed and infests large areas of Western Australia, Northern Territory and Queensland, amounting to over 800,000 hectares primarily along waterways. Although prevention of spread is urgent, it is made difficult because seeds are dispersed by water.
Prickly acacia is a woody shrub imported from India and Pakistan as a fodder and shade tree in the early 1900's. It is now a major weed and is known to infest over 6,000,000 ha of arid and semi-arid Queensland, with small infestations in other states. Prickly acacia costs the grazing industry $5 million annually due to reduced production and increased management costs. The industry now acknowledges that the impact of this species significantly outweighs the benefits gained from shade and drought fodder.
Introduced animals
The major introduced species affecting rangelands-goat, rabbit, pig, buffalo, donkey, camel, horse, cat, fox and cane toad-now make up over 10% of Australia's fauna. Impacts on production include competition with livestock for food and shelter, predation on stock, land degradation, especially in localised areas of high feral population, and spread of diseases.
Impacts on biodiversity include predation, competition for food and shelter and displacement of native species.
The National Feral Animal Control Program aims to reduce the damage to agriculture and the environment caused by feral animals. It is administered by the Bureau of Rural Sciences and the Biodiversity Group of Environment Australia.
Goats were introduced to Australia in 1788. By 1993 there were an estimated 2.6 million feral goats. The one million animals mustered each year do not seem to have altered the population. Goats help spread disease among domestic stock. They prefer shrubs and trees for fodder, and prevent regeneration of perennial plants by eating seedlings. Goats impact dramatically on ecosystems that have evolved without browsing animals. However, there is no evidence of their damaging large areas in the absence of other herbivores. Control is difficult due to their high mobility and rate of increase.
The domestic pig was first introduced into Australia in 1788 with the First Fleet to provide food for early settlers. Pigs are the most popular game animal and the feral pig meat industry is worth $10 - $20 million annually. Pigs will eat almost anything. They prefer tender green vegetation, fruit, grain and also eat rodents, lizards, frogs and insects. They prefer wetter areas and do most habitat damage to wetlands, marshes and watercourses. They are responsible for spreading the seeds of exotic plant species such as Mimosa pigra.
Rabbits were realised in 1859 onto a property in Victoria for sport and food. Since then they have spread over most of the continent. The rate of spread across Australia was the fastest of any colonising mammal in the world. Through grazing, rabbits prevent regeneration of native plants and compete with livestock. The rabbit is considered a pest and landowners are legally obliged to control numbers.
The cane toad was introduced to the Cairns area in 1935 in an attempt to control beetle pests. They were unsuccessful at controlling the insects and have since become a major pest. They are still colonising Australia and their range is extending west across the Gulf of Carpentaria. Cane toads impact native fauna by consuming vertebrates and invertebrates, poisoning predator species who attempt to eat them and competing with native species for food and habitat.
Buffalo occupy the northern costal floodplains of the Northern Territory. Buffalo are a potential reservoir for bovine diseases and are a serious pest because they cause soil compaction, trampling and destroy most of the vegetation in the area they inhabit.
The domestic cat was released to control mice and rabbits in the 19th Century and has since spread over the entire continent. Cats feed mainly on young rabbits but also take small native mammals such as ring-tailed possums, bush rats and marsupial mice. Current control methods are unreliable and not effective over large areas.
The European red fox was released for recreational hunting and its early spread and establishment was associated with the introduction and spread of the rabbit - a staple food. The fox is now common in most parts of Australia except in humid tropical regions. The fox may represent a threat to newborn livestock and poultry but is recognised as a major threat to small and medium sized native animals as a direct result of predation.
Native vegetation clearing
Change in the extent of native vegetation indicates loss of habitat and is a key part of biodiversity monitoring and assessment.
Australia-wide change in the extent of native vegetation has not yet been compiled. The Australian Greenhouse Office has Landsat data (as part of the National Carbon Accounting System) that will provide an Australia-wide assessment of vegetation change. Linking these data to the Audit's National Vegetation Information System will provide information on types of native vegetation and its loss.
In some states, data collection systems (often linked to clearing permits) allows collation of finer-scale information on clearing and when this becomes readily available it will be able to replace data derived from analysis of the Australian Greenhouse Office clearing register.
The following table is an example of the type of data available in the National Vegetation Information System
| Major Vegetation Group | 1997 (ha) | 1997 (km2) |
|---|---|---|
| Rainforest and Vine Thickets | 660,052 | 6,600.52 |
| Eucalyptus Tall Open Forest | 1,324 | 13.24 |
| Eucalyptus Open Forest | 933,516 | 9,335.16 |
| Eucalyptus Low Open Forest | 4 | 0.04 |
| Eucalyptus Woodland | 16,441,400 | 164,414 |
| Acacia Forest and Woodland | 9,574,928 | 95,749.28 |
| Callitris Forest and Woodland | 311,540 | 3,115.4 |
| Casuarina Forest and Woodland | 1,198,676 | 11,986.76 |
| Melaleuca Forest and Woodland | 113,456 | 1,134.56 |
| Other Forests and Woodlands | 248,328 | 2,483.28 |
| Eucalyptus Open Woodland | 4,472,080 | 44,720.8 |
| Tropical Eucalyptus Woodland/Grassland | 220,616 | 2,206.16 |
| Acacia Open Woodland | 323,864 | 3,238.64 |
| Mallee Woodland and Shrubland | 5,323,616 | 53,236.16 |
| Low Closed Forest and Closed Shrubland | 84,500 | 845 |
| Acacia Shrubland | 1,371,728 | 13,717.28 |
| Other Shrublands | 33,8092 | 3,380.92 |
| Heath | 1,288,468 | 12,884.68 |
| Tussock Grassland | 4,528,920 | 45,289.2 |
| Hummock Grassland | 85,856 | 858.56 |
| Other Grasslands, Herbland, Sedgeland and Rushland | 30,848 | 308.48 |
| Chenopod Shrub, Samphire Shrub and Forbland | 785,528 | 7,855.28 |
| Mangroves, tidal mudflat, samphire and bare areas, claypan, sand, rock, salt lakes, lagoons, lakes | 155,628 | 1,556.28 |
| No data | 128,040 | 1,280.4 |
Further Information
- Environment Protection and Biodiversity Conservation Act 1999 List of Key Threatening Processes and Threat Abatement Plans
- State of the Environment (SoE) Fire Regimes of Australia (Department of Land Administration)
- Tropical Savannas CRC
- Bureau of Meteorology (BOM) for other climate information products
- "Indices of change in ecosystem function at the national scale using AVHRR NDVI data" report (by S.Cridland, 2000) (PDF - 380 KB)
- Summary (Indices of change in ecosystem function at the national scale using AVHRR NDVI data)
- "Indices of change in ecosystem function (cover) for northern South Australia using Landsat TM data" report (by A.Brook, R.Tynan & M.Flemming, 2001) (PDF - 1.7 MB)
- Summary (Indices of change in ecosystem function for northern South Australia using Landsat TM data)
"Regional land condition and trend assessment in Tropical Savannas" report (by R. Karfs, R. Applegate, R. Fisher, D. Lynch, D. Mullin, P. Novelly, L. Peel, K. Richardson, P. Thomas & J. Wallace, 2000):
- Summary
- Final report (PDF - 2 MB)
- Technical Summation (PDF - 4 MB)
- The East Kimberley/VRD Region - the Ord-Victoria WA/NT (PDF - 2 MB)
- Appendix (PDF - 2 MB)
- "Incidences of extreme climatic events" report (by S.Cridland, 2000) (PDF - 264 KB]
- Summary (Incidences of extreme climatic events)
- "Change in land tenure/land use" report (by M. Gutteridge, W. Hall & A. Hanna, 2000) (PDF - 844 KB)
- Summary (Change in land tenure/land use)
- "Intensity of land use" report (by M. Gutteridge, G. Stone, A. Hanna, J. Kingston & W. Hall, 2001) (PDF - 7.48MB)
- Summary (Intensity of land use)
- Rangelands-Tracking Changes final report
- Rangelands-Tracking Changes summary report
- Rangelands-Tracking Changes summary report (PDF - 11.5 MB)
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