Importance of early selective thinning in the development of long-term stand stability and improved log quality: a review

There is increasing evidence that a decline in the practice of selective thinning in Britain may in part explain an observed reduction in log quality in recent years. The decline in use of selective thinning has been primarily influenced by the low value of early thinnings together with increasing pressure to make a financial surplus on harvesting operations. Since systematic or delayed thinning, used to improve the short-term economics, may result in stand instability, the no-thinning option has been widely adopted in stands at risk of damage by wind and snow or where a financial surplus on early selective thinnings is not possible. This review sets out to demonstrate that non-commercial, early selective thinnings can be seen as a long-term investment in future log quality and value without compromising stand stability. Low thinnings do not greatly destabilize stands even on exposed sites if carried out on time and will improve stability in the long term. While early low thinnings are unlikely to make a financial surplus on the operation, they significantly enhance the production of quality 'green' logs in comparison with a no-thinning regime. Evidence presented in this paper indicates that the wood-using industry is willing to pay a premium for this quality. The combination of these factors suggest that non-commercial, early low thinnings can be seen as a long-term investment using discounted cash flow methods. The implications of other silvicultural strategies, such as wide initial spacing, respacing, chemical thinning and self-thinning mixtures, on stand stability and wood quality are also discussed.