Who is this for?
This information is for pastoralists, resource managers, government staff and others with an interest in the productivity and maintenance of rangeland pastures.
What is pasture condition?
The condition rating of a rangeland pasture is based on the presence and density of desirable perennials. Desirable perennials are necessary to provide productive and reliable pasture (resilience) in the highly variable climate of the Pilbara.
For each pasture type, the current condition of the pasture species is compared to the optimal condition that could be expected, taking into account the potential of the site (landscape position, soil, climate, vegetation). The term ‘health’ is sometimes used, meaning that all parts of the ecosystem are present and working well together.
Pasture condition is rated as good, fair or poor, depending on how close the current condition is to the optimal condition. What you expect to see at a site in good, fair or poor condition depends on the pasture type that occurs there. This means that to use the guide, you have to identify the pasture type first.
Some pastures, for instance hardpan mulga shrub pastures, even in good condition have very low density and mostly bare ground.
Identifying pasture type
Identify the pasture type before you assess the pasture condition. The guide gives descriptions and photographs of good, fair and poor pasture condition for 12 of the most common pasture types in the Pilbara.
Each pasture type has its own page, which includes a list of plant species associated with the pasture type, grouped into desirable, intermediate, undesirable and stability desirable species. The relative proportions and density of these 3 classes largely determine pasture condition.
Soil type and position in the landscape, along with vegetation, are used to distinguish between the 12 Pilbara pasture types.
Pasture condition decline
Condition declines when any of the following changes occur:
- desirable species are replaced by less-desirable species
- reduced plant cover increases the proportion of bare soil
- erosion accelerates
- production of palatable perennial species declines
States and transitions – are changes in pasture condition and composition reversible?
It is always possible to improve pasture condition, but it may not be possible or practical to return to the original pasture composition and condition.
There is good experience in the Pilbara showing that improving pasture condition from poor to fair, or fair to good, is possible, largely through destocking and reseeding. It is harder to go from poor to fair than from fair to good, and it is generally very hard to go from severely degraded and eroded to fair.
When desirable perennial species are lost through adverse conditions and overgrazing, they are commonly replaced by less-desirable perennial or annual species, and form a new stable state. Change from one state to another is referred to as a ‘transition’. These new states can be relatively resistant to change, creating essentially permanently altered pasture types that may have a lower grazing value than the original pasture.
Changes in the species composition of the pasture as a consequence of various pressures (grazing, fire and drought) and introduction of new species may not always be directly reversible or even desirable.
For instance, where degraded pasture is colonised by buffel grass, this change is likely to increase productivity and reduce the risk of soil erosion more quickly than trying to achieve the original species composition.
Assessing pasture condition
For reliable long-term assessment of pasture condition, we recommend installing monitoring sites across each pasture type. The recording method is different for shrublands and grasslands.
When is the best time to assess pasture condition?
Pasture condition can be assessed at any time of the year because it depends on the species present and their density rather than the amount of standing pasture (biomass). However, it is usually easier to identify particular species early in the season; later in the season, fire or heavy grazing can make identification difficult.
How often should pasture condition be assessed?
The frequency of assessment depends on how quickly the pasture condition is changing. Yearly assessments allow early changes to be detected; on the other hand, since change is sometimes gradual, it may be easier to detect change over longer intervals. Climatic conditions are very variable in the Pilbara, so assessments may be needed over 10 or more years to see reliable trends, particularly in shrubland pastures.
When changing management to improve or alter pasture condition or type, we recommend assessing condition more often.
Choosing sites for assessing pasture condition
Variability is normal in the rangelands. No matter how hard you try to select a uniform site to assess, you will find variation in the species present compared to nearby areas, and variation in other aspects such as grazing pressure. Do not worry about variation; it is more important your assessment sites broadly represent the pasture type and condition of that area.
If there are two or more distinct pasture types in the area you are assessing, select a site within each type. Avoid sampling across the boundary between different pasture types (e.g. where ribbon grass pasture grades into hard spinifex pasture).
Keeping track of changes
To show whether condition is improving, declining or staying the same:
- record the pasture condition at the same site over a number of years; photographs of the site each time you assess its condition provide good additional information – note the date, pasture type and condition
- keep livestock management and climate records for management areas.
This information can be used to monitor the effect of management practices and seasonal conditions on pasture condition and productivity.
Each pasture type has characteristic plants known as ‘indicator species’ that indicate the condition of the vegetation for the purpose of pastoral use. Plants in the species list for each pasture type have been divided into 4 categories of indicator value: desirables (decrease under excessive grazing pressure), undesirables (increase under excessive grazing pressure), intermediates and stability desirables (no indicator value, but perform important landscape functions) (Table 1).
Some species are more sensitive to grazing than others in the same category. For example, ruby saltbush (Enchylaena tomentosa) is much more easily removed from the bluebush–saltbush pasture type than tall saltbush (Rhagodia eremaea), but both are classified as decreasers.
By being able to distinguish plant species, land managers can see if their management is giving the desired result.
Desirable perennials can herbaceous or woody. These live for more than 1 season and they last through the dry times, providing feed and protection from erosion. There are very few desirable annuals – see Ptilotus axillaris in soft spinifex plain pastures in the Pilbara, Western Australia.
Intermediate and undesirable species may be annual or perennial. Annual plants generally live for only 1 season. They can provide short-term feed following a good growing season, but have little bulk. Annual grasses tend not to last through the dry season, and so provide little protection from erosion.
Desirables / Decreasers
Undesirables / Increasers
Stability desirables / No indicator value
Species which decrease in numbers as grazing pressure increases, e.g. barley Mitchell grass (Astrebla pectinata), silver saltbush (Atriplex bunburyana). These are highly palatable, preferred species.
Species which may initially increase under grazing, but being moderately or slightly palatable, later decrease under continued increasing grazing pressure, e.g. three-winged bluebush (Maireana triptera).
Species that increase in number with grazing pressure, e.g. crinkled cassia (Senna artemisioides subsp. helmsii), feathertop three awn (Aristida latifolia). These are unpalatable species. They can also include palatable species that are poisonous to livestock, e.g. black soil poison (Stemodia kingii).
Species which are largely unaffected by grazing and which usually only decrease in number after natural disturbance such as hail damage or fire, e.g. mulga (Acacia aneura), hard spinifex (Triodia spp.), eucalypt trees. These species are not palatable or only slightly palatable (or out of reach of browsing animals). They confer stability on the landscape and contribute to important landscape functioning processes such as water retention and nutrient cycling.
Good pasture condition: what to look for
- Desirable species are dominant and vigorous.
- Some intermediate perennial and annual plants may be present.
- Undesirable species are rare.
- Desirable species are reproducing; seedlings or young plants may be present.
- Groundcover is optimal for the site; sites with good soils and higher rainfall can generally support a higher density of plants than sites with shallow stony soils or lower rainfall.
- Where plants have been grazed down or burnt, the butts of desirable species remain alive.
Fair pasture condition: what to look for
Intermediate species make up 30% to 50% of the stand; desirable and undesirable species take up roughly equal proportions of the remaining space.
Or: intermediate species dominate, with only a few desirable and undesirable species.
Or: only desirable species are present, but the density of plants is low, with substantial (or increasing) bare areas in between.
- Desirable species may show signs of reduced vigour, for example, smaller butts or fewer stems.
- Seedlings or young plants of desirable species may be hard to find.
- Groundcover is less than optimal for the site; there may be patches of annual plants early in the season that dry up or are trampled and blow away, leaving areas of bare ground later in the year.
Poor pasture condition: what to look for
Undesirable and intermediate species dominate.
Or: undesirable species dominate, as dense stands or with variable amounts of bare ground.
Or: bare ground dominates, with occasional desirable species or other perennial plants spaced far apart.
- Desirable species are rare or absent.
- Any desirable species remaining are usually stunted and unproductive.
- Intermediate species may be present, but are less frequent compared to fair condition.
- Groundcover may be sparse or patchy.
- Large bare areas may be evident, particularly later in the season when the annual plants have dried up or been trampled and blown away.