12 TIMBER PRODUCTS IN THE BUILT ENVIRONMENT It is well established that deforestation pean forests act as a sink for atmospheric car- and land-use change play a significant bon dioxide. The benefits of atmospheric carbon role in contributing to increased levels of storage can continue if timber is used in long- life products, such as the built environment. atmospheric carbon dioxide (CO2). Ho- wever, forestry can also contribute to These benefits are even greater if timber is used reversing this trend, because at- as a substitute for building materials with a mospheric carbon can be sequestered in higher associated embodied energy for any gi- ven functional unit [2]. Although forests can be forests. used to produce timber, they can also be mana- ged for other additional benefits such as biodi- versity, recreation, landscape, prevention of soil erosion or flooding. Although forest biomass can be used as a sink for atmospheric CO2, as the trees reach maturity the carbon inventory approaches a plateau [3]. Thus, in order to ensure continued sequestrati- on of atmospheric carbon, it is necessary to harvest the biomass (and replant) and utilise this material in long life products, thereby stor- ing the atmospheric carbon for longer periods [4]. Providing markets for timber ensures the survival of the forestry industry and provides an incentive for further planting. The felling of Photo: Lone Ross Gobakken trees in well managed forests never exceeds the NAI, and the trees that are removed are repla- ced by manual restocking, of natural regenera- tion. If the felled timber is used immediately for The process of tree growth utilises atmospheric energy production, then the carbon that is rele- carbon in the production of wood biomass. ased by combustion is not immediately replaced When timber is harvested, this sequestered by the re-growth of the forest; resulting in what carbon can continue to be held in products that is called a ‘carbon pay-back time’ [5]. Although are derived from trees. The growing of trees is there are benefits if the burning of fossil fuel is good, but so is harvesting them, provided it is avoided through the use of biomass, much grea- done sustainably. ter benefits arise if the harvested timber is used in long-life products. European forests have increased in area by approximately 2% in the past decade. The net Furthermore, when the end of life of a timber annual increment (NAI) of European forests product is reached, the wood it contains can (the amount of wood that is created by trees continue to be used as a carbon store by being every year minus natural losses) is in the region cascaded down through lower value products of 770 million m3, while annual fellings are (e.g. a timber beam can be chipped to make par- around 480 million m3 [1], meaning that Euro- 43 ticleboard), keeping the atmospheric carbon in However, there is no significant material in use the materials carbon pool for longer [6]. Once in the construction sector that is made from the maximum physical use has been made of the atmospheric carbon dioxide and only a few that wood, it can finally be burnt with energy reco- can be cascaded down through several life cy- very, returning the stored carbon dioxide to the cles. There are no other significant construction atmosphere and also reducing the amount of materials that can be incinerated at the end of fossil carbon released through substitution. life-cycle without release of fossil carbon. Tim- ber is the ideal material for the circular econo- Timber is one of very few structural materials mies of the future. that is derived from atmospheric carbon dioxi- de. It can be used to replace alternative con- References struction materials which have much higher associated embodied energies, providing addi- [1] EUROSTAT tional benefit [7]. The use of timber provides [2] Lippke, B., Wilson, J., Meil, J., Taylor, A. additional benefits by supporting the economic (2010) Characterizing the importance of carbon health of the forestry sector, such a rural em- stored in wood products. Wood and Fiber Sci- ployment, providing incentives for replanting ence, 42(CORRIM Special Issue), 5-14. and for forest management for a variety of other [3] Perez-Garcia, J., Lippke, B., Comnick, J., Man- benefits. The forestry industry uses certification riquez, C. (2005) An assessment of carbon and chain of custody schemes, linked to forest pools, storage, and wood products market sub- management plans to ensure that the timber is stitution using life-cycle analysis results. Wood produced and harvested in an environmentally and Fiber Science, 37(CORRIM Special Issue), responsible and sustainable manner. 140-148. [4] Storaunet, K.O., Rolstad, J. (2002) Time since When determining the benefits of using timber death and fall of Norway spruce logs in old- compared to other construction products, the growth and selectively cut boreal forests. Cana- arguments can become complex because rival dian Journal of Forest Research, 32(10), 1801- industries see timber as a threat to their market 1812. share. The production of all construction mate- [5] Holtsmark, B. (2012) Harvesting in boreal rials involves emissions of carbon dioxide asso- forests and the biofuel carbon debt. Climatic ciated with the processing, transport and main- Change, 112, 415-428. tenance during the functional lifetime. Analysis [6] Skog, K.E., Nicholson, G.A. (1998) Carbon of the benefits of using different materials re- cycling through wood products: the role of quires that a common functional unit is consi- wood and paper products in carbon sequestra- dered and that performance in service is known tion. Forest Products Journal, 48(7/8), 75-83. and that final disposal is considered. Such ana- [7] Gustavsson, L., Pingoud, K., Sathre, R. (2006) lyses often rely heavily on assumptions and this Carbon dioxide balance of wood substitution: can (and does) confuse the comparisons. Many Comparing concrete- and wood-framed buil- studies clearly show the benefits of substitution dings. Mitigation and Adaptation Strategies for by using timber products, but other studies ha- Global Change, 11(3), 667-691. ve been produced that can show the opposite. NB Forest Policy and Research Briefs Callum Hill, Norwegian institute of bioeconomy research Published xxx WSE – Northern European Network for Wood Science and Engineering Nordic Forest Research (SNS) www.nordicforestresearch.org .