Desmestas

Thinning and spacing in forest plantations

When a plantation is established for the production of quality timber, whether from broadleaves or conifers, a planting density is usually used that is higher than the density it should have at the time of felling, so, Over the course of the rotation, the density must be reduced as the trees grow, until a much lower density is reached at the mature age of the plantation.

As with coppice in the case of broadleaves, we are aware of the work it entails for some forest owners to carry out thinning and spacing, but these treatments are essential to ensure that the better-formed trees can spend their final years with sufficient room to grow as large as possible and produce timber of good size, without competition from the poorer-formed ones.

 

Difference between thinning and spacing

The first cuts made in a plantation are called clearings.clearings in Castilian Spanish) and, generally, have no commercial value as timber, although in some cases the extracted stumps could be used for energy purposes as biomass, stakes or chipping. The felling of the stumps that may already have commercial value is called thinning (clear in Spanish.

These two tasks, in addition to being necessary to ensure the trees finish the rotation in the best possible condition for optimal growth, allow some economic return to be obtained before the final harvest and thus help care for the future trees.

They will also help to prevent pests and diseases by removing the affected plants.

Thinning is common in natural regeneration or seedings where it is carried out in the early years to reduce the density of the regeneration, which in these cases is often very high.

 

How it should be thinned out

Both thinning and spacing out should be carried out gradually, without causing sudden imbalances in the trees' growth. Excessive thinning can do more harm than good, as, among other things, it exposes the canopy to excessive wind. It is common to carry out thinning or initial clearings at the same time as pruning to reduce costs on debris removal, and because both operations must be accompanied by the selection of future trees. It would be a pointless exercise to prune trees that are going to be cut down shortly afterwards.

It is important to always maintain a good balance between height and diameter, which is known as taper. Trees that grow with excessive thickness may have a high taper and are at greater risk of damage during thinning or spacing operations and of failing to reach the commercial diameter of interest by the planned rotation.

All care, such as pruning, should be focused on the selected future trees. It is pointless and uneconomical to prune defective trees that will be cut down before the final harvest.

 

What should be cut?

Both in the case of thinning and in the case of spacing out, the best trees should be reserved, evenly distributed throughout the plot, which will be those utilised in the final cut. In these intermediate cuts, the trees with the most defects will be felled, which are listed from most to least severe:

• Dry
• Stem bifurcating below 6 m in height
• Crooked shaft
• Domination by other feet
• Those who have mastered their feet best
• Stem with cankers (except in the case of chestnut, which should be a priority for removal)
• Abundant and thick branches
• Poorly-shaped cup
• Forked stem above 6 metres in height
• With large wounds in the shell
• Affected by pests or non-serious diseases

 

When to make an intermediate cut

It is very difficult to establish a schedule for thinning and spacing out. The timing will depend on the tree species, the quality of the land, the chosen planting pattern, previous work carried out, etc., so it is recommended that if you lack experience in this type of work, you consult a specialist, especially in the case of broadleaf woodland.

As a general rule, it can be said that a thinning or a spacing out should be carried out progressively in several interventions, taking into account the final density and rotation of the forest stand. If a forest stand has had a suitable spacing-out programme from the outset, it is advisable that at least 5 years pass between each one, a period sufficient for the trees to grow and for a situation of competition among them to be restored. As for the maximum percentage of trees to be cut, 50% can be considered for clearfelling and 25% for thinning.

Given that the most commonly used planting layout for broadleaves in Galicia is 4×4, we are starting from an initial density of 625 plants per hectare, or in the case of having planted at 3×3, the most common in pine or eucalyptus plantations, this represents a density of 1,100 trees per hectare. The following table shows the average number of feet per hectare that should be present at the time of felling in plots of different forest species, when they are destined for the primary production of quality timber such as sawtimber, pulpwood, veneer, beams and other structures.

 

Final density of forest plantations intended for the production of quality timber

 

Species	Density at least 5 years before the final cut
Birch (Birch specimen	From 250 to 350 feet per hectare
American oak (Red oak)	200 to 250 feet per hectare
Native oak (English oak)	From 100 to 300 feet per hectare
Chestnut treeChestnut specimen	From 150 to 250 feet per hectare
Cherry treePrunus specimen	From 50 to 100 feet per hectare
Poplar (Poplar specimen	From 200 to 400 feet per hectare
Eucalyptus (Eucalyptus specimen	From 100 to 150 feet per hectare
Ash (Ash tree specimen	From 100 to 150 feet per hectare
Walnut (Walnuts specimen	From 70 to 100 feet per hectare
Oregon pine (Pseudotsuga menziesii)	200 to 300 feet per hectare
Country pine (Pine maritime)	From 200 to 400 feet per hectare
Pine insignis (Radiata pine)	From 200 to 500 feet per hectare
Sweet chestnutAcer specimen	From 100 to 300 feet per hectare
Sequoia (Sequoia specimen	From 50 to 200 feet per hectare