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Growing quality hardwood timber from our young broadleaf woodlands

Growing quality hardwood timber from broadleaf woodlands requires a selective management approach and it is therefore important to identify early the quality trees within the woodland. These trees are known as Potential Crop trees (PCTs). Ian Short & Jonathan Spazzi, Teagasc Forestry, have advice

Potential Crop trees (PCTs)

PCTs are selected trees of high quality that are favoured during thinning operations. Some of these trees will go on to produce the final and intermediary quality hardwood saw-logs.

There are five criteria used for the selection of PCTs:

  1. Disease-free – PCTs must be free from disease as there is no point in selecting trees that are diseased
  2. Stability –trees need to be well rooted and offer long term stability for long term retention. 
  3. Good stem quality – PCTs have the best stem form of those trees available within that specific location. Trees with good stem form are straight with no major defects preferably up to 6 m height, but often 4 m or 5 m is the best achievable 
  4. Good vigour – PCTs have good crowns and good growth rate. They tend to be larger than the average size. Remember: the crown of the tree is the engine of the tree. The larger the crown is, the more photosynthesis and greater growth rate there will be
  5. Good distribution throughout the woodland – PCTs should be relatively evenly spread out throughout the woodland 

When selecting PCTs, it is good practice to view the tree from two perpendicular sides – a tree that looks good from one side can look poor from the other side and therefore should not be selected.

PCTs should be selected and marked with a ring of permanent paint so that they can be identified from all sides. One easy method to help ensure the correct number of trees are selected and with a good distribution is the two-stick method.

You can see more about the two-stick method in the video below 

But what is thinning and why is it needed?

Thinning is a requirement for the management of productive quality hardwood timber. It is the removal of a proportion of trees to provide space and resources to enable the selected quality trees to continue their steady development.

It is normally done when the height of the woodland is approximately 8-10 m, though if the broadleaf species was planted in mixture with a conifer species which has grown taller than the broadleaf, thinning may be required earlier to remove this conifer nurse species and protect the broadleaf.

When growing broadleaves with an objective of producing high quality sawlog, thinning is done to maintain the quality and productivity of the selected PCTs whilst also maintaining or enhancing the general health and biodiversity of the woodland.

During first thinning operations the main routes of access for all subsequent thinning will be established by introducing a system of woodland racks, in conjunction with timber lorry roading access, if required.

Diseased trees should be removed during a thinning operation. This will help maintain the general health of the woodland by helping to prevent spread of disease.

Removing competitors to PCTs

Competitors to the selected Potential Crop Trees are targeted for removal.

Competitors are those trees that are competing with PCTs in the canopy. Two, three and, in some cases, up to four competitors per PCT can be removed. They tend to be approximately as tall as the PCTs and their canopy will often be encroaching into the PCT canopy space, therefore competing for light. Removing trees that are small or are being suppressed by the surrounding trees will have little impact on the PCTs growth. When removing competitors the focus should be on the trees that are competing strongly in the canopy with PCTs.

Anything between 30% and 50% of the standing trees may be removed in a first thinning, dependent on site, species and other factors. tall tree thinning canopy

It is good practice to mark the trees to be removed to facilitate the felling operation.

When the tree felling is being carried out, it is important to know what log lengths are required for the markets to which they will be sold with the firewood market being the most common and readily available market.

The buoyant firewood market together with support from the DAFM Woodland Improvement Scheme provides a suitable vehicle to apply much-needed selective management to grow our young broadleaf woodlands into an added-value timber resource in years to come while also helping to safeguard their heath and a high biodiversity value.

Contributors: Ian Short is a Teagasc Forestry Research Officer & Jonathan Spazzi is a Teagasc Forestry Advisor.

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