Thinning your trees
Thinning is cutting down unwanted trees so that growth can be encouraged in those remaining (the final crop trees). It is a relatively low cost operation, but the intensity and timing can have a major effect on forest growth and profit.
Wood production planting
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:
- restrict branch development
- promote straight stem growth
- provide a good selection for the final crop
- close the canopy to suppress competing weeds.
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.
Conditions for successful production thinning
- There is a market for the thinnings.
- The topography is sufficiently easy to allow low cost and low site impact harvesting.
- The forest is sheltered enough to reduce the risk of wind throw.
- Skilled contractors are available to minimise damage to crop trees.
- The economic advantages of the intermediate yield exceed the benefits of the larger trees in a direct regime, that is no production thinning.
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:
- thin to waste
- keep the number of thinnings to a minimum.
When to thin trees
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.
Initial tree spacing
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.
How to thin trees
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:
- branching habit
- spacing in descending order of importance.
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.
More information on thinning
Check out the below websites for more information on thinning.