Farm Ireland

Monday 22 April 2019

Thinning the crop to fatten your profits

Thinning optimises the return from your forest crop as long as it is properly carried out, writes Steven Meyen

Completed road for thinning
Completed road for thinning

The bread and butter tree of Irish forestry is Sitka spruce. Many Sitka spruce forests were established during the '90s and are now being thinned.

When a new farm forest is established, 2,500 trees are planted per hectare. After a number of years, they begin to compete with each other as they grow. If the forest is not thinned, it is likely that by the time the crop is ready for clearfelling, the number of trees per hectare would be about 1,400, the remainder having died off due to natural competition in the crop. The average tree volume would be about 0.4m3.

However, if some trees are removed at various stages during the life of the crop, the remaining trees have more growing space, resulting in fewer trees but of greater quality and size. In a forest that has been thinned throughout its life, there should be about 500 trees per hectare at the time of clearfell, with each tree having a volume of 0.8m3. This is twice the size of trees in an unthinned plantation. This results in a more valuable crop as larger trees command a much higher price as they are used for higher value products.

Not thinning will result in a larger number of smaller sized trees, with a likely reduction in crop value.

This means that, if properly carried out, thinning optimises the return from your forest crop, provides periodic returns as the crop matures and creates valuable access into and through the forest. Thinning also improves the biodiversity value of the forest and gives you a wider range of options if you are interested in adopting close to nature forestry principles, also known as continuous cover forestry.

Now that I have nailed my colours to the mast by making a case for thinning, it is important to decide first of all if the trees are suitable to thin. You need to keep in mind that thinning may not be an option where the site is very exposed, wet and/or unstable, has restricted access or where it is not economically viable.

To help in making these decisions, it is essential that inspection paths are cut through the crop. This allows access into and through the crop so that the suitability for thinning can be assessed.

This process is called 'brashing' and involves removing branches to head height between two lines of trees when the trees are 10 to 12 years of age. Parallel paths should be 50 to 100m apart depending on the size of the forest. Take appropriate safety measures if using a chainsaw. There is a short, handy Teagasc video on YouTube demonstrating brashing.

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First thinning can take place as early as 13 to 15 years in a very productive crop of Sitka spruce, while it can be as late as 22 to 24 years on an unproductive site.

Teagasc has developed a very simple and straightforward tool to assist you in deciding if the crop is ready for thinning.

The Thinning Ready Reckoner uses a 'traffic light' system by comparing the number of trees per hectare with the average tree diameter and is available from

Effective and timely planning is crucial because between one thing and another, it can easily take two years or more before actual thinning will take place.

In particular, improving access into and through the forest and applying for a felling licence can be time consuming.

As the loading of timber is illegal on public roads, even small forests will require road construction to provide timber loading areas. Construction should be completed one to two years in advance so the road can settle before harvesting operations commence.

Planning permission is required to create access from the forest on to the public road. Attractive roading grants are currently available from the Forest Service, Department of Agriculture, Food and the Marine (DAFM).

A General Felling Licence is required to carry out thinning and usually remains valid for five years.

Apply well in advance to the Forest Service.

Once the licence is in place, you decide when thinning needs to be carried out within that five-year window. Application forms as well as worked out examples are available from

The first thinning operation in conifer crops normally involves removing lines of trees to get access into the crop.

Normally one line in seven is completely removed and inferior trees are selected for cutting out of the remaining lines. This leaves the crop nicely spaced and very accessible.

As a general rule, a maximum of a third of the existing number of trees and a corresponding third of the crop volume are removed in the first thinning.

Once the first thinning is completed, the crop is allowed to grow on for a further three to six years before it is thinned again.

First thinning should be all about improving the quality of your growing asset.

This can be done by removing inferior trees while allowing the valuable trees to grow to full maturity. Don't be tempted to sell off the family silver for short term gain. You will be paying the price later.

If you want to find out more about thinning, make sure to come to Teagasc's Talking Timber events taking place on Tuesday, September 8 at the McWilliam Park Hotel, Claremorris in Co Mayo and on Tuesday, September 15 in the Mount Wolseley Hotel, Tullow, Co Carlow.

Steven Meyen is a Forestry Adviser with Teagasc.

The greater the risks, the greater the effort needed

Managing safety in forestry operations is of paramount importance to all involved parties.

There may now be many links in the chain between 'forest owner' and 'forest worker'.

Whether you are a forest owner or timber buyer, contractor or subcontractor, you have legal duties to fulfil in order to ensure people's safety and health is not put at risk during, or as a result of, forestry operations.

The law requires that during the planning and carrying out of forestry operations, a number of safety and health duties be fulfilled, including:

l preparing written risk assessments;

l selecting suitable equipment for the job;

l protecting public safety and health;

l setting out safe working procedures;

l ensuring operators are competent;

l supervising and monitoring the work.

Depending on the contractual relationship, different role-holders may share duties.

To successfully manage safety and health, you need to co-ordinate your activities with others and pass information up and down the contract chain.

To help this flow of information and to ensure the right people carry out the right tasks, the Code of Practice for Managing Safety and Health in Forestry Operations sets out four management roles:

* the Landowner role;

* the Forestry Work Manager (FWM) role;

* the Contractor role;

* the Sub-contractor role.

Within any forestry contract, you need to identify which of these roles falls to you and carry out the appropriate tasks. Depending on how the contracts are organised for a particular work-site, you may pick up more than one role.

Within each role, the effort demanded by a particular task depends on the complexity and extent of the risks involved.

The greater the risks, the greater the effort needed. The following table provides an overview of the four different management roles.

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