Options for managing invasive native scrub

Causes of native scrub encroachment

Native scrub encroachment is a result of complex interactions of fire, grazing and seasonal conditions.

Seedlings of woody species are susceptible to competition from established perennial grasses, particularly in the first summer after establishment, as well as to fire. In overgrazed grassland, these controls are either weakened or removed. 

Woody vegetation thickening is also often seen to occur in waves associated with sequences of high rainfall years. If the summer following shrub germination is wet, seedlings are able to survive despite the presence of perennial grasses. If they are not subsequently destroyed by fire, the thickening scrub will soon overtop the grass layer and reduce forage production. In these circumstances, invasive native scrub can be seen as a cause of land degradation.

Why it is a problem

The most obvious impact of thickening woody weeds and native scrub is on the amount of forage available for livestock.

• A reduction in carrying capacity caused by the impact of invasive native scrub on the production of grass and herbage.
• Woody weeds are unpalatable to the livestock traditionally run in these areas.
• Dense scrub interferes with mustering and stock management operations. 

Where woody scrub encroachment has reached the point where the country is difficult to traverse and forage production is minimal the case for action is obvious.

Integrated invasive native scrub management

Management of native scrub must be an integrated, on-going process that is part of normal property management including:

• control of total grazing pressure through fencing and control of water points
• tactical grazing to maintain perennial grasses under varying seasonal conditions, and treatment of regrowth. 

Management must comply with the Invasive Native Species (INS) part of the Land Management Code.

The nature and timing of these activities will vary from property to property and even paddock to paddock but planning to address all of them should be part of both short and medium-long term management planning.

Maintain open areas

Open areas provide the highest economic return and shrub cover does not need to increase greatly before economic return is serious impacted. 

The cost of maintaining open areas is much lower than the cost of returning encroached areas to an open state, so ensuring that existing open areas are maintained should always be the first priority of INS management. 

This will require monitoring of open areas, particularly following seasonal conditions likely to lead to shrub establishment, and treatment of newly established plants while they are still small (<50 cm). 

Prioritise remaining areas for treatment on the basis of expected costs and benefits, and the ease of incorporating INS management into overall property management.

Develop a property plan

• Use satellite imagery to map areas of open country and INS-affected zones.
• Overlay INS map with other property layers (fences, tracks, water points).
• Record INS density (open, scattered, moderate, dense).
• Note dominant species and age structure (seedlings, young, mixed, mature) to guide treatment choice.

Identify priority areas for treatment

• Give highest priority to maintaining open areas—treat isolated plants and small clumps early.
• Target perimeter of infestations to prevent spread into open areas.
• Consider local factors (species difficulty, erosion risk, water retention benefits).
• Assign lower priority to dense infestations unless strategic reasons exist.
• Ensure workload matches available labour capacity for ongoing management.

Decide between grazing or carbon credits

• Evaluate whether land should be managed for grazing or enrolled in carbon projects.
• Factor in economics: carbon price, sequestration potential, and long-term opportunity costs.
• Consider biodiversity impacts of locking up land for carbon credits.

Develop a post-treatment strategy

• Plan for grazing management under a tactical grazing framework.
• Set objectives for each paddock and monitor indicators (ground cover, INS regrowth height).
• Implement Total Grazing Pressure (TGP) control—fencing and water point management.
• Schedule follow-up treatments (spot spraying, grubbing, fire) before regrowth exceeds 50 cm.
• Exclude grazing immediately after treatment to allow pasture recovery.

Summary of treatment options for INS