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
Published 19/08/2015 | 02:30
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.