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Wood procurement strategies. Characterisation, selection and sorting of wood with respect to industrial needs, wood and fibre properties and logistics

The physical manufacturing of wood based products starts at harvesting in forest stands. Different wood sources have different wood and fibre properties. This has been clearly stated by a systematic sampling of different log heights from individual trees of different ages (maturity) growing under different climatic and soil and other stand conditions. The EuroFiber project has developed, improved and adapted models predicting fiber (e.g. fiber length, fiber width, cell-wall thickness and basic density) wood properties of logs from Norway spruce growing in many parts of northern and central Europe. By measuring or assessing tree diameter, age and height of sample trees from a stand, wood and fiber properties can be predicted with commonly acceptable accuracy at the pile level. Pilot and mill trials included in the EuroFiber project clearly indicate that fiber length, fiber width, cell-wall thickness and wood basic density all have relevance for TMP-based products.

There are several opportunities to improve different production chains by using these models in forestry practice. We have now started to introduce applicable prediction models (from different sources including EuroFiber) into software components useful for forest planning systems, tree harvesters, logistics and industrial production planning systems.

Three examples of forestry applications are given below: 1.Wood procurement strategies, 2.Stand selections and 3. Sorting by wood and fibre properties.

- Wood procurement strategy:
The properties of wood vary: from one region to another, among stands, among trees in a given stand and within individual trees. Given the low haulage costs, it is often prudent to use all the acceptable raw material that can be harvested close to a mill. Over longer haulage distances, however, it becomes more important to supply wood having the desirable properties. When there are two mills sharing an intermediate zone, and their processes and product mixes differ, they can both benefit by splitting the raw material between them according to the wood properties. This makes for more dynamic procurement areas, with raw-material supplies being better suited to the needs of the individual mills. Examples of other situations in which it may be advantageous to adjust the procurement area according to the wood properties include:
-- Areas in which there is a surplus of timber; and

-- Where a mill increases its consumption of raw materials and, hence, its procurement needs.

In principle, this strategy is much the same as that used at present, whereby the haulage distance is weighed against the availability of raw materials and the needs of the mill. However, wood properties provide an added dimension to logging and haulage planning. Thus, with the aid of some simple rules of thumb, predictive models and modern planning techniques, an overriding strategy for raw-material supplies, closely adapted to the needs of the individual mill, can now be implemented.

- Stand selection:
The wood properties of trees vary widely even among stands in the same tract. Pulpwood from thinning, for example, has different properties from that harvested in final felling. Similarly, old stands yield different properties from those of younger stands; fertile soils produce different pulpwood from that grown on poor-quality soils... and so on. This knowledge can be used in scheduling stands to be felled, or to allocate pulpwood from a particular stand to a given mill, in order to improve the properties of the raw material and, thereby, to reduce unwanted variations.

- Selection by wood and fibre properties:
A large percentage of the variation that occurs in the wood and fibre properties is found within and among trees in a given stand. Consequently, it is possible to improve the properties in the pulpwood by sorting the wood into a greater number of assortments than is customary today.

However, handling more assortments increases the cost of felling, extraction and road haulage. Beside the EuroFiber project Skogforsk has developed computer software (Sortkost) that calculates the cost of sorting in conjunction with harvesting. If the revenue covers the cost of sorting, it pays to increase the number of assortments extracted from the stand. If several additional assortments are to be extracted, the harvester can be programmed, using the models, to determine the average wood properties in the individual logs. Data that can be used include the length and diameter measured by the harvester, together with the stand age, latitude and elevation of the stand. Thus, it will be possible to optimise the sorting strategy continuously to meet the woodproperty and volume requirements specified by the mills and, at the same time, to take into account the wood, logging and logistics costs.

Informations connexes

Reported by

Skogforsk - The Forestry Research Institute of Sweden Research Institute
Skogforsk - Uppsala Science Park
751 83 Uppsala