Single tree selection and thinning

Single tree selection and thinning are silvicultural systems used to encourage forest growth or regeneration by harvesting single trees or small groups of trees.

The following video explains how single tree selection and thinning practices can:

• boost forest growth
• support regeneration
• reduce pest and disease risks
• help you meet Private Native Forestry (PNF) Code requirements.

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Video transcript

Single tree selection and thinning

There’s a lot to consider when planning harvesting operations in your forests. So we are here to help and show you how single tree selection and thinning can be used to improve forest health and productivity as part of your forest management.

Thinning is useful in forests with stands of similar aged younger trees. It’s used to provide more growing space and increase the diameter growth rates for retained trees and is focused on long-term productivity. It helps trees reach commercial size sooner by giving the retained trees a greater access to resources like light, water and soil nutrition. Thinning can also benefit overall forest health and hygiene by removing trees that are stressed and potential sources of pest and disease outbreaks.

When choosing which trees to target with thinning, you can use a particular diameter range, spacing, or focus on diameter classes by thinning from below. Thinning from below removes suppressed, sub-dominant and smaller diameter or poorer quality co-dominant trees. It also retains bigger diameter or better quality co-dominant and dominant trees.

A good rule of thumb to guide how heavily to thin is to aim to provide enough space between the crowns of the retained trees for the crowns to enlarge, just enough to touch each other again by the time the next scheduled thinning operation, while still maintaining your basal area requirements.

Single tree selection is usually applied to forests with stands of trees of different ages growing beside each other. It’s used to remove single trees or smaller groups of older trees, to provide room for younger trees to grow, or to provide limited room for regeneration of less intolerant species.

Whether you’re choosing thinning or single tree selection, the PNF Code prescribes that the average stand basal area after harvesting must not be less than the code of practice.

Every forest is different. Thinning and single tree selection are just some of the tools in forest management. To get advice on what best suits your property, contact your area’s farm forestry officer. For more information, contact Local Land Services. We’re here to help you.

About single tree selection

Single tree selection is usually applied to forests with differently aged stands of trees growing beside each other. 

Single tree selection removes single trees or a small group of older trees to provide room for younger trees to grow.

When using this method, consider the structure of the forest. Single tree selection benefits unevenly aged and mixed species forests, where many trees are not big enough to harvest.

About thinning

Thinning is useful in forests with stands of similarly aged, younger trees. 

Trees compete for resources including light, nutrients, and water. As a forest stand develops and trees compete for space, some trees will grow faster and taller and begin to overshadow neighbouring trees.

Thinning provides more growing space for retained trees. The focus is on improving the overall health of the forest, or on increased diameter growth rates for long-term productivity. 

Thinning can target trees of a particular diameter range, or it can focus on crown classes by thinning from below or above.

Crown classes

The classification of trees within a developing stand into crown classes reflects:

• how much light the tree receives
• its competitive position in the canopy
• its growth rate. 

There are 4 distinct crown classes. 

• Dominant - receives light from above and sides.
• Codominant - receives light from above and some sides.
• Subdominant - receives light only from above.
• Suppressed - overtopped by other trees. 

Codominant and subdominant trees do not reach their full potential due to overshadowing.

Suppression is due to crown shyness that causes small trees to bend away from large trees. 

Thinning from below removes suppressed, subdominant and smaller diameter or poorer quality codominant trees. This maximises resources for the largest, healthiest trees.

Thinning from above removes some dominant and codominant trees to open the canopy and provide sunlight to the younger trees underneath. This makes space and resources available for retained trees to increase growth. 

Requirements under the PNF Codes of Practice

Section 5.2 of the PNF Codes of Practice outlines the requirements for single tree selection and thinning. 

To maintain a long-term, adequate forest structure, there are limits to which trees can be harvested using this method. This is calculated using 'basal area'.

To meet these requirements, complete a stand basal area assessment:

1. before a forestry operation to ensure the existing basal area supports compliance
2. during any forestry operation to ensure continuing compliance with the PNF Code.

Understanding basal area

Under the PNF Codes, there are some important definitions.

Tree basal area – the cross-sectional area of a tree trunk measured at breast height over bark; think of it as the surface area of a cut stump at a height of 1.3 m.

Stand – an identifiable and mapped area of the forest.

Stand basal area – the sum of the basal area of all live trees in a stand. Usually expressed in square metres per hectare (m2/ha).

Minimum stand basal areas – calculated as an average using multiple measurements across the relevant forestry operational area (allowing for a reasonable degree of silvicultural flexibility and practicality in planning forest operations).

Relevant forestry operational area –

• For current forestry operations – those parts of the stand within the area described in the current Forest Management Plan (where the current forestry operation occurs)
• For past forestry operations – those parts of the stand where previous forestry operations occurred under the PNF Code.

Using basal area for single tree selection and thinning 

Single tree selection and thinning operations must not reduce the stand basal area below the minimum requirement across the net harvestable area of a Forest Management Plan. Refer to the specific Code for your forest type for more information.

Calculating stand basal area

The following video explains:

• how to measure your basal area
• choosing locations for sample points
• use of a dendrometer for measurement
• calculating your basal area
• understanding the PNF Codes.

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To calculate the average basal area:

• Use a minimum number of sample points according to the size of the assessed harvested area.
• The harvested area only includes areas where forestry operations may occur. Do not include roads, tracks and log landings.

• Sample points must be within connected forest areas. Do not include isolated patches of forest.
• The sample points must be located systematically across the harvested area with a minimum distance of 60 metres between points.
• Samples must be taken using angle count sampling or fixed area plot measurements.
• Where fixed area plot samples are used, plots must be 50 m x 20 m in size.

Benefits of single tree selection and thinning

Single tree selection and thinning promotes:

• regeneration of shade-tolerant species
• the growth of preferred species
• the growth of individual trees.

These forest management treatments can enhance your forest in many ways.

• Improving stand quality where there is a large proportion of low-value trees with defects.
• Improving tree growth by allowing retained trees greater access to resources.
• Removing trees before they die enables the harvesting of viable timber - this can also reduce fuel load and associated fire risks.
• Improving stand hygiene and removing potential sources of infestation (stressed trees are more vulnerable to pest and disease outbreaks).
• Increasing the amount and diversity of other native (non-tree) species.

Things to consider

Under the PNF Codes, single tree selection and thinning must not create canopy openings. If you want to create canopy openings, you will need to use Australian Group Selection or variable retention.

Shade tolerance

Understanding the shade tolerance of your tree species can help guide the most effective silvicultural treatment to encourage forest regeneration or rehabilitation. 

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. 

For more information visit Shade tolerance and forest regeneration for guidance on effective silvicultural treatments to encourage forest regeneration or rehabilitation.

Field and tree markings

LLS recommends field and tree markings when undertaking single tree selection and thinning. This will help ensure that everyone involved understands which trees to harvest and which trees to keep.

For more information, refer to the Field and tree marking guide.

Monitoring and improving regeneration

Following a harvest event, you must monitor regeneration. This will help you to ensure good regeneration is occurring.

A harvest event may warrant additional treatments. These may include pest and weed controls and stock exclusion to minimise competition and damage to regeneration. Supplementary planting is an option where natural regeneration is lacking.

For information on understanding and monitoring regeneration, refer to the Forest regeneration guide. 

You can contact Local Land Services for assistance to monitor or calculate forest regeneration.