The cut-to-length method

The Cut-to-Length method

CTL is responsible forestry

The cut-to-length method is a modern, nature-friendly logging method. In the cut-to-length method, trees are harvested in the forest with equipment developed for the purpose, which makes the method effective and environmentally friendly.

The cut-to-length method is often thought of as a Nordic logging method. The cut-to-length method was originally developed based on the desire to optimize the efficiency of the production chain of logging and wood processing by removing overlapping work stages. In cut-to-length, trees are processed in the forest according to use, which enables high value yield and an effective logistic chain. This enables the flexible application of different thinning and regeneration felling models in accordance with good forestry practices, because the machines are easy to manoeuvre and trees are processed efficiently one by one.

Equipment and costs

In the cut-to-length method, the harvesting equipment usually consists of a team of two machines, i.e. the harvester and the forwarder. The harvester fells, delimbs and measures the trunks, and cuts them into assortments ordered by the mill. Assortments refer to logs extracted from trunks for different uses, including different sawlogs, veneer logs, bolts, pulpwood and material for bioenergy use. The automatic system of the harvester takes care of the optimal usage of the trunks into most valuable assortments. This is called automated bucking.

The forwarder transports the trees to the roadside and makes a separate pile for each assortment. Long-distance transport to the mill is taken care of with a timber truck featuring a crane for loading.

In the tree-length method, correspondingly, the harvesting equipment consists of a feller for felling the trees, a skidder for pulling the intact trunks to the roadside, and a delimber or a processor. The delimber removes the limbs and cuts the tops of the trunks. Often, a slasher or a processor is also needed by the roadside if the trunks are so long that they must be cut for long distance transport. Loading into the timber truck is carried out with a crane transported in the truck or with a separate loader. In hilly terrain, the tree-length method can also be carried out by a cable yarder team. In this method, the trunks are hoisted up steep hills with specifically developed winches.

The tree-length method requires more machines than the cut-to-length method. In the cut-to-length method, two machines are typically needed for work requiring three or four machines in the tree-length method. Fuel consumption per harvested cubic meter is lower with the cut-to-length method than with the tree-length method because one tree is only processed by two machines: the harvester and the forwarder. Other running costs of machines are also lower in the cut-to-length method.

The cost structure of cut-to-length is different from the tree-length method because logging circumstances such as slopes, long forest haulage distances and soft ground have a significantly lower effect on the productivity of the machines than in the tree-length method. Therefore, the overall productivity of the machine chain is more level and easier to manage.

Why is the cut-to-length method more responsible?

The machines used in the cut-to-length method feature a crane reaching up to approximately 10 metres, and the trunks can be cut in the forest, which enables efficient selective thinning’s. In selective thinning, a dense forest stand is thinned and its best trees are left to grow in accordance with forestry recommendations. This guarantees that the value of the forest will increase and it will yield high-quality wood in later thinning or final felling. Properly carried out thinning prevents the forest stand from becoming too dense and the trees from drying out, as well as keeping the forest viable. This significantly reduces the risks of insect damage and fire, among other things.

In the cut-to-length method, the trees are delimbed and bucked in the forest. This means that the nutrition-rich top and limb slash consisting of leaves/needles, branches and tops are left in the forest. In nutrient-poor soil in particular, this ensures that the trees left growing or the regeneration seedlings draw enough nutrients from the soil. Alternatively, part of this slash can be collected for bioenergy use, but even in that case, the nutrients from the leaves and needles remain in the forest. Top and limb slash is also used to even up the machine driving paths in the forest to reduce the strain caused by the machines on the terrain. This has a massive impact on the formation of ground damages and possible erosion. If the cut-to-length method is carried out properly, the surface pressure on the ground caused by the machine is comparable to a human footprint. In the tree-length method, these nutrients are carried to the roadside and out of the forest, and because the trunks are transported with limbs intact, the slash cannot be used on the machine driving paths.

In the cut-to-length method, the space requirement for landings is small because the wood is not processed at the landings. In the cut-to-length method, wood transport takes place as soon as possible after the wood has been brought to the roadside. Thus, stockpiles will not grow too large. Quick turnover decreases the amount of bug infestation. The tree-length method requires a large roadside landing since that is where the delimbing and part of the bucking take place. In the tree-length method, if the top slash is not used as bioenergy, the landing must be cleaned after harvesting because the large amount of limb/top slash creates an uncontrollable risk of fire. This cleaning is often carried out by burning, which releases a large amount of carbon dioxide into the atmosphere.

The cut-to-length method makes it possible to harvest even small logging areas cost-effectively, since there are fewer machines to move to the work site and they are relatively easy to move due to their light weight. For small sites, special Dual machines have also been developed that can function as both harvesters and forwarders. In this case, just one machine is sufficient for carrying out the work. 

For the above reasons, the cut-to-length method enables responsible forestry that greatly intensifies the growth of the forest. A growing forest is an excellent carbon sink because as trees grow, they bind a great amount of carbon dioxide from the atmosphere. Along with low terrain damage, this is one of the most important environmental issues relating to responsibility.

The cut-to-length method gives a higher yield from valuable wood material and a lower wood wastage

The cut-to-length method allows significantly more bolts to be produced in initial thinning than the tree-length method. This is because the harvester optimises each trunk accurately before cutting it. Therefore, visual estimation is not used for cutting the trunk.

Additionally, when using the cut-to-length method, even a small amount of special wood can be separated and transported cost-effectively to the mill. Examples of this include different log qualities, veneer log and poles. Due to this, the cut-to-length method enables better volume and value yield because the whole tree is utilized effectively. In tree-length, wastage is often higher.

Logistics in a key role

When implemented correctly, the long-distance transport of wood to the mill can be carried out at a lower cost and more effectively in the cut-to-length method than in the tree-length method.

For example, in the cut-to-length method, logs are transported directly to the sawmill, veneer logs directly to the plywood mill and pulpwood directly to the paper or pulp mill. For this reason, the transport distance is shorter than in the tree-length method, in which the entire trunks are typically first transported to the sawmill, where they are unloaded and the part suitable for sawing is cut off.

The rest becomes pulpwood and is chipped, loaded into a truck and transported to a paper or pulp mill. Thus, in the tree-length method, there are more processing stages for pulpwood than in the cut-to-length method and, for example, the transporting distance of pulpwood is nearly always longer than in the cut-to-length method.

In addition, round trips can be utilized in the transportation for the cut-to-length method. This means that, for example, when sawlogs have been picked up at the logging site and taken to a sawmill, a load of pulpwood can be picked up near the sawmill and taken to a paper mill. With efficient logistics, unnecessary empty running can be avoided to reduce carbon dioxide releases.

Further processing is quick

In the cut-to-length method, logs are cut in the forest. Therefore, they can be sorted at the sawmill into batches with similar diameters before the sawing process. A batch like this can be sawed with a high line speed because all the logs are approximately of the same diameter. The settings of the saw do not have to be adjusted between logs.

In the tree-length method, logs are typically sawed in the order in which they are removed from the trunk. Therefore, the top diameter is different for each log, and for this reason, the settings of the saw must be adjusted for each log. This, in turn, leads to lower line speed and lower efficiency.

Ponsse specialises in forest machines designed for the cut-to-length method and in related information systems.