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Specific aspects of forestry and forest products to be considered in LCA

For LCA in the forestry and forest products sector, special aspects such as "the positive effects of forest utilization and timber use", "problems related to the allocation of environmental burdens to by-products" and "disposal of waste" should be taken into account.

Environmental effects related to the use of wood-based products

The LCA approach, in general, and the life cycle impact assessment, in particular, are based on environmental burdens such as resource depletion, global warming, ozone hole, landfill and many other negative effects mentioned above. The positive effects on environment resulting from the use of renewable materials should also not be forgotten, even though the consideration of such positive effects is not foreseen in ISO 14040-14043.

Roundwood production in forests is the first phase of any product life cycle. Consequently, forests as the major supplier of roundwood shall also be included in the studies dealing with LCA of wood-based products. The environmental effects caused by forestry activities and operations are divided into positive and negative effects as described below (Scharai-Rad et al., 1996).

Positive effects

Negative effects

  general positive functions of a diverse ecosystem

  use of solar energy and carbon dioxide and its conversion into wood as an important fuel and raw material

  forest and wood function as carbon sinks

  wood is renewable and, by sustainable forest management practices, permanently available

  forest functions as air cleaner

  forest protects soil, water and wildlife

  forest has an important recreation role

  forests are part of the landscape

  influencing the natural processes of the ecosystem "primary forests" (e.g. changing plant societies and age structure of trees)

  use of fossil energy for the necessary operations

  use of land and soil

The qualitative and quantitative inclusion of all the positive effects in the inventory and impact analysis is difficult. An objective judgement about forest as a sustainable resource and wood as the most important renewable material cannot be achieved without, at least, a qualitative consideration.

Another problem is the effect of exogenous sources of toxicity. Forests close to power stations or busy roads are exposed to toxic heavy metal emissions which are adsorbed by trees. The ash analysis of timber often shows the existence of these toxic metals although the forest itself is not responsible for the occurrence of such toxicity. Consequently, the results of impact analysis are often worse than what they should be.

Problems related to the allocation of environmental burdens

Residues in forest and in the wood industry are in reality by-products predominantly used as raw material and as renewable fuel. They can be of the following categories:

thinning and harvesting residues;

sawmill residues (slabs, offcuts, trimmings, edgings, chips, sawdust, bark);

residues of furniture industry (planer chips, sawdust);

residues from veneer slicing and veneer peeling process (solid wood pieces, peeler cores, veneer residues);

timber in building constructions; and

waste paper for recycling.

In the sawmills the recovery depends among others upon the roundwood diameter, technology, variety and size of final products. A recovery of 50 percent (e.g. Scandinavia) means that 50 percent of employed roundwood is converted to residues of different types which could be used for various purposes. Within the framework of inventory and impact analysis, the operating materials such as oil, water, chemicals, etc., and the energy consumed for sawn timber production shall not be allocated only to the sawn timber as main product. The sawn timber would be otherwise overloaded with environmental burdens while products based on sawmill residues (e.g. pulp, MDF, particle board) would benefit from this unjust allocation method. The example described below illustrates the importance of allocation with and without consideration of by-products.

Example

In Germany the sawn timber recovery amounts to 62 percent for softwood and 66 percent for hardwood. Moreover, around 30 percent of sawmill residues are utilized economically, so that they can be regarded as by-products. A considerable part of the sawn timber production is used as building material for roof construction. As shown in Table 1, the energy necessary for roof construction amounts to 988 MJ/m structural timber (timber used in construction) if the total energy consumption is allocated proportionately to main product and by-products (residues). If energy is also allocated only to the main product, the total consumption is 1 412 MJ/m.

Table 1: Energy consumption for roof building related to 1 m structural timber
(Adebahr, 1995)

 

Energy input (MJ/m)

 

By-products not considered

By-products considered

1. Wood production in forest

166.8

166.8

2. Sawmill

884.6

532.6

3. Carpentry/joinery

20.0

20.0

Sum of 1 + 2 + 3

1 071.4

719.4

4. Transportation

340.4

268.7

Total (1 + 2 + 3 + 4)

1 411.8

988.1

Carbon cycle

Wood is particularly characterized by its CO2-neutrality and the volume of CO2 released by burning and/or biological degradation is the same as CO2-uptake necessary for the photosynthesis. In the case of sustainable forest management, the volume of annually allowable cut does not exceed the annual growth and, therefore, wood will be permanently available.

Considerable amounts of waste wood (used products) is utilized as recycling material or as fuel, but the very last step of each wood product is burning or biological degradation resulting in the release of CO2 and other trace gases. As described above, the inventory analysis indicates the relevant inputs and outputs of a product system. By burning and/or biological degradation of wood, the oxidation process takes place creating CO2 and other gases which are listed under the output side of inventory analysis but, due to the fact that during the oxidation process oxygen is taken up from the atmosphere, it is not possible to obtain an accurate balance between inputs and outputs.

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