When planting trees for wood production (not shelter or aesthetics) it is usual to plant more trees than what is required for the final crop to:
Thinning opens the stand out. This gives the final crop more crown and root potential, and improves tree health, vigour and diameter growth. Root development also increases the trees stability against wind.
There are 2 options for thinning – production thinning and waste thinning.
Production thinning involves extracting the thinnings and selling the produce. In the right circumstances this can generate an income during the life of the forest.
Waste thinning (or silvicultural thinning) leaves the trees to waste where they fall. Unless profitable production thinning can be done at the correct time it is advisable to:
The timing and age at which thinning is carried out depends on wood product, initial tree spacing, tree species, and markets.
If trees are being grown for pruned sawlogs, thinning should be done at about the same time as pruning (and no longer than 3 to 4 months after pruning for Radiata pine). Tree crops being grown to produce unpruned sawlogs are generally thinned once they are about 10 to 14 metres tall.
A first thinning of trees planted close together (that is, 2,500 stems per hectare) will need to be earlier than those planted at a wider spacing (that is, 800 stems per hectare).
Each species has characteristics which will influence the timing of thinning. For example, Douglas fir is shade-tolerant and wind-firm, so thinning timing is more flexible than for Radiata pine.
The availability of suitable markets for produce from a production thinning operation can affect the timing.
If a stand has recently been pruned, the selection component of a thinning operation is simplified. Cull trees are those that are left unpruned.
If thinners are selecting the crop trees, they should select the correct number of acceptable trees from the non-defective trees, according to the following criteria:
Chainsaws are generally the most suitable tool for thinning operations, although machines can be used where topography is suitable, especially when production thinning.
Chainsaw work can be dangerous, and safety is extremely important. Forest growers planning to do their own work are advised to attend training courses or employ experienced operators.
Check out the below websites for more information on thinning.