Forests need thinning to feel well. Thinning secures proper growth, value growth and health of the forest. Ponsse specialises in the cut-to-length forest machines, in which stems are already cut for different purposes in the forest. The method plays an important part in responsible forestry.  

Trees and roots need to compete over nutrients in an unthinned forest, which is also susceptible to snow, wind and other damages.  

“Thinning is intended to protect the wellbeing and growth of forests, as well as secure the supply of raw material. Thinnings are necessary when the aim is to take good care of forests,” says Tuomo Moilanen, Ponsse’s forestry specialist and area director of Germany and Austria. 

During thinning, trees with a low potential are removed: damaged, broken and low-quality trees. High-quality trees with the best ability to grow are left standing.  

Successful thinning is affected by pre-clearing and stand tending. When it is time for thinning, the cut-to-length forest machine’s significance in avoiding damage to remaining trees and the ground are key.  

At the beginning of the 19th century, selection cutting was the primary trend in Finland, which is the exact opposite of thinning, in that the best trees are selected and felled.  

“When the best trees are always selected for harvesting, the worst trees remain to give birth to the next generation, reducing the quality of the forest,” Moilanen says.  

In responsible silviculture, forest productivity remains high, decade after decade. Thoroughness and biodiversity are emphasised in harvesting. Unnecessary damage to the forest is to be avoided and valuable assets, such as decayed wood, are to be taken into account.

“Valuable habitats are left untouched. No trees are removed, and they are not accessed by the forest machine. Responsible thinning is carried out during the appropriate time of the year depending on the forest and soil. Thinning done during the wrong time of the year causes unnecessary damages to the forest,” Moilanen adds. 

In a properly tended forest, thinning is easier. Pre-clearing also makes the operator’s work easier and improves the quality of work: visibility is better after part of the undergrowth has been removed from around trees before thinning.   

Ponsse specialises in the cut-to-length method, in which stems are already cut for different purposes in the forest, such as sawn or pulp logs. The method plays an important part in responsible silviculture.  

“One of the largest advantages of the CTL method is that the ground can be protected during felling by leaving twigs and treetops on the trail. Both the harvester and forwarder will then drive on a protected trail, placing less strain on the ground,” says Moilanen. 

In the CTL method, forwarders carry loads from forests, without dragging any trees against the ground. Instead, in the tree-length method, whole trees, including branches and tops, are brought to the roadside. Thinning with the cut-to-length method enables the valuable raw material to be collected undamaged.

“In the tree-length method, it is challenging to maintain a high level of quality. When long stems are felled in the forest during first thinning, it will be difficult to carry them away without causing damage,” Moilanen says. 

In thinning the 20-metre gap between trails should be maintained. Unnecessary detours in the forest create more trails, which should be as straight as possible. Stability is required from the machine, and the operator needs to have excellent visibility over the entire work area, so that trees can be thinned effectively without damaging any other trees.  

During first thinning, in particular, forests are often dense, and the average stem size is small. To reach a sufficient level of productivity, small stems need to be processed accurately and quickly. The machine’s crane geometry and control system must support effective and precise operations.  

“During their shift, the operator processes hundreds or even over a thousand stems. Working must be easy so as not to tire the operator. Here, ergonomics play an important part,” says Moilanen. 

Trees removed during thinning may also be damaged or unwanted. Unwanted trees may have been left in the area as seedlings, or they may be much larger than other trees. 

“When thinning from above, large trees must also be removed. This sets requirement for the harvester head’s size and the crane’s power. Thinning from above cannot be done with small forestry machines,” Moilanen says. 

Ponsse’s forest machines have wide tracks, increasing the surface area towards the ground and reducing the surface pressure. The pressure directed at the ground must be sufficiently low so that the forest machine does not damage remaining tree roots and the ground unnecessarily.