Prior to the era of impregnated timber, the heartwood of two boreal conifers, Scots pine (Pinus sylvestris L.) and Siberian larch (Larix sibirica Ledeb.), was used in construc-tions prone to decay. Today, when environmentally compatible alternatives to protect wood are searched for, the interest in the exploitation of naturally durable heartwood has revived.
The durability of heartwood is provided by extractives. For example, in Scots pine stil-benes and resin acids make the heartwood moderately decay resistant whereas the fla-vonoid taxifolin defends the heartwood of Siberian larch. In theory, the mechanisms of extractives in prolonging the service life of dried timber could be based on the retarding the sorption of water, or on the inhibition of degradation processes of decay fungi. Ac-cording to our studies, the role of extractives in pine and larch is mainly inhibitory but the exact mechanism we can only speculate about.
We are often asked what the possible targets are for the use of naturally durable heart-wood products. The answer is dependent on how long service life and what kind of life cycle the customers appreciate when getting e.g. wooden garden fittings or out-of-door deckings. We suggest that uniform pine and larch heartwood products are a substantial choice in non-covered service situations above ground (the hazard class 3 described in the standard EN 335-1). Evidently, in a permanent contact with ground or water the service life of untreated heartwood is often too short and thus an effective impregnation or modification of wood is needed.
Keywords: Heartwood, Decay resistance, Natural durability, Service life
Authors
Venäläinen M.
Finnish Forest Research Institute, Punkaharju Research Unit, Punkaharju
Harju A.
Finnish Forest Research Institute, Punkaharju Research Unit, Punkaharju
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