About Australian Group Selection
Australian Group Selection (AGS) is a silvicultural system where trees are harvested in groups (small patches or stands). This creates an opening in the forest canopy.
AGS is usually used for the following:
- to support regeneration of shade intolerant species
- as a strategy to restore productivity to degraded forests
- to help re-introduce age and structural diversity and/or species diversity to monocultural forests.
If your forest has a lot of shade intolerant species and/or is in poor condition, AGS may be appropriate.
Note that AGS is not permitted under the Cypress-Western Hardwoods Code.
Figure 1: Diagram of a forest area before and after Australian Group Selection harvesting.
Shade Tolerance and Forest Regeneration
AGS is a forest management method suitable for shade intolerant species. For example, those recognised as being very intolerant or intolerant as outlined in the table below.
Trees compete for resources including light, nutrients, and water. Tolerance to competition for resources varies between tree species. Trees classed as shade-tolerant can withstand and regenerate in shade. They can also grow in the presence of competition for resources with adjacent canopy trees.
Shade intolerant species may:
- fail to regenerate
- show restricted growth
- become suppressed in the presence of an adjacent canopy of trees.
Shade intolerant trees can grow quickly when they have little competition and access to direct sunlight.
Eucalypts are typically shade intolerant. While no eucalypt can be classed as truly tolerant, there is a range of tolerance amongst eucalypt species. Understanding the shade tolerance of your tree species can help guide the most effective silvicultural treatment to encourage forest regeneration or rehabilitation.
| Shade tolerance | Species (examples) | Growth characteristics | Silvicultural considerations |
|---|---|---|---|
| Very intolerant | Flooded Gum | Rapid growth when given access to a high level of light | Require larger canopy openings that increase light penetration and improve regeneration |
| Intolerant | Blackbutt, alpine ash, silvertop ash, stringbark | Fast growing but poor development when overtopped by other species | Require larger canopy openings that increase light penetration for regeneration |
| Intermediate | Spotted gum, river red gum, brown barrel | May establish and persist under canopy trees but can become suppressed or have restricted growth | Require medium sized canopy openings that increase light penetration and improve regeneration |
| Tolerant | Tallowwood, white mahogany, red mahogany, grey gum, ironbarks | Slow to medium growing species, can establish and persist, but in restricted form under other trees | May develop in small gaps |
| Very tolerant | Turpentine, brush box, cypress pine | Slow growing species that often exist in growth restricted form in the understory | Able to respond to very small canopy openings after the death or removal of individual trees |
Australian Group Selection requirements under the PNF Codes of Practice
The Private Native Forestry Codes of Practice (PNF Codes) outlines the requirements for AGS (Section 5.3) and provide guidance for measuring forest regeneration (Appendix C).
Under the PNF Codes, harvest operations may produce canopy openings to encourage the regeneration of forest stands with shade intolerant species.
You cannot use AGS in areas of mass movement of soil or rock. There are also some species prescriptions in Appendix A of the PNF Codes (for example, the blackstriped wallaby and eastern pygmy-possum). The recorded presence of these species in an area limits the use of canopy openings.
A canopy opening is an area greater that 0.1 hectare in size, measured from the dripline of the trees that form the canopy perimeter, where any retained vegetation (other than significant features such as hollow-bearing or feed trees) is less than one half of the stand height.
Figure 2: A canopy opening within undisturbed forest.
The maximum area of an individual canopy opening must not exceed 0.5 hectares. The sum of canopy openings must at no time exceed 20% of the net harvestable area per landholding for the duration of the PNF Plan.
AGS cannot occur within 100 metres of the edge of a canopy opening:
- within ten years of the completion of harvest operations, or
- until the forest stand within canopy openings has reached 10 metres or more.
Canopy openings can be an irregular shape to maximise light penetration and optimise the area to boundary ratio. This can:
- encourage forest regeneration
- account for existing landscape features
- account for significant habitat features like hollow bearing trees, dead standing trees and feed trees.
Under the PNF Codes, landholders must monitor forest regeneration, composition, and condition at 2, 6 and 10 years after a harvest operation.
Where the forest within an AGS gap is not regenerating in a way that maintains (or improves on) preharvest forest conditions, landholders must put in place regeneration management actions.
Benefits of Australian Group Selection
AGS is suitable for promoting regeneration of shade intolerant species. This is because it eases competition on saplings by letting more light reach the forest floor. If your forest of shade intolerant species is in poor condition, AGS can be an effective forest management method to improve the forest health and productivity. It will help by improving regeneration and creating a mosaic of different aged trees across the landscape.
What to consider when planning Australian Group Selection operations
Forestry operations are permitted after the approval of a Forest Management Plan (FMP). Your FMP should include:
- a map that highlights the location of silvicultural treatments
- a written component outlining details of the proposed AGS operations including the planned activities to promote regeneration and post-harvest management.
Location of operations
When planning forestry operations, consider your long-term forest management objectives. Remember that additional canopy openings cannot be created within 100 metres of the edge of an existing canopy opening within ten years of the completion of harvest operations, or until the forest stand within canopy openings has reached 10 metres or more.
AGS and Single Tree Selection cannot occur within 100 metres of a canopy opening. Limiting operations in this manner provides a mosaic harvesting approach and helps to maintain structural diversity of the forest.
When planning the size and shape of canopy openings to meet your forest management objectives, think about:
- the species composition of your forest and what is the optimal size canopy opening for their regeneration
- any significant landscape or habitat features in the vicinity of your planned operations that you should avoid
You may use irregular shapes to maximise light penetration and optimise the area to boundary ratio. This will help to encourage forest regeneration and account for existing landscape features. It will also account for significant habitat features (such as hollow bearing trees, dead standing trees, feed trees).
Figure 3: Irregular shaped canopy openings.
During and after operations
When undertaking AGS, use of field and tree markings is recommended. This will help ensure that everyone involved in the operation understands which trees to harvest and which trees to retain.
For more information on how to undertake field and tree markings refer to the Field and Tree Marking in Farm Forestry Field Guide.
Following a harvest event, you must monitor regeneration within gaps. This will help you to ensure good regeneration is occurring.
Gaps may warrant additional treatment such as:
- weed control,
- feral species controls
- stock exclusion
- to ensure you minimise competition and damage to regeneration.
Refer to the Forest Regeneration in Farm Forestry Field Guide for further information about regeneration and to the PNF Codes (Appendix C: Calculating Forest Regeneration) for guidance on measuring forest regeneration.
How to help regeneration after Australian Group Selection
Fire management
After harvesting, the debris in the gap created by AGS may be burnt to create an ash bed in which a future crop of shade-intolerant species can regenerate. Before undertaking fire management, check whether it is suitable for your forest. Consider the species composition, ground cover and threatened species. Refer to Section 7 of the PNF Codes for further information about fire management in PNF. For advice on conducting fire management contact the Rural Fire Service.
Reducing grazing and browsing pressures
Grazing by stock can impact the growth of new seedlings or young trees. You can help the forest regenerate by limiting grazing through:
- grazing exclusion by fencing
- rotational or tactical grazing.
Effective management of pest species such as deer, rabbits and goats may also help reduce browsing pressures on seedlings in early-stage regeneration forests.
Weed management
Weeds compete for resources with native species and can hinder native regeneration. Ensure that you are aware of common weeds in your forest and how to treat them effectively.
Forests can be particularly prone to weeds following disturbances including harvest operations. Think about planning weed control as a part of your forest management planning. Ensure appropriate biosecurity measures are undertaken during machinery operations.
For further resources on weed management please refer to your Regional Strategic Weed Management Plan or contact your nearest Local Land Services office.
Mechanical disturbance
You can use mechanical disturbance to disturb the soil and reduce understory competition. This creates a favourable seedbed for regeneration. You may use mechanical disturbance in place of fire to stimulate seedling regeneration of obligate seeder species, where burning is not desirable or is likely to pose management issues. If undertaking mechanical disturbance, ensure the topsoil is not removed.
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