It is expected that a warming climate will have an impact on the future productivity of European spruce forests. In Scotland, Sitka spruce (Picea sitchensis (Bong.) Carr.) dominates the commercial forestry sector and there is growing pressure to develop alternative management strategies to limit potential economic losses through climate change. This review considers management options to increase the resilience of Sitka spruce dominated forests in Scotland. Given the considerable uncertainty over the potential long-term impacts of climate change, it is recommended that Sitka spruce should continue to be planted where it already grows well. However, new planting and restocking should be established in mixtures where silviculturally practicable, even if no-thin regimes are adopted, to spread future risks of damage. Three potentially compatible species with Sitka spruce are western hemlock (Tsuga heterophylla (Raf.) Sarg.), grand fir (Abies grandis (Lamb.) Lindl.) and Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and all form natural mixtures in its native range in North America. The predicted windier climate will require a range of management inputs, such as early cutting of extraction racks and early selective thinning, to improve stability. The potential to improve resilience to particularly abiotic damage through transforming even-aged stands into irregular structures and limiting the overall size of the growing stock is discussed.

This study examined the wood properties of 24-year-old Sitka spruce ( Picea sitchensis (Bong.) Carr.) progenies with highly contrasting growth rates. The progenies were established as part of a breeding programme to improve growth rate and stem form. Trees from three progenies were selected with a high growth rate relative to an unimproved control of directly imported material from the Queen Charlotte Islands (QCI), British Columbia, Canada. Trees from a further three progenies were selected that displayed a similar growth rate to the QCI control. At the time of sampling, the fastgrowing progenies had a mean volume gain over the QCI and slow-growing progenies of ~70 per cent. Trees from the fast-growing progenies were found to have significantly larger branches, less latewood, and more compression wood in comparison with the QCI control and the slow-growing progenies. On the other hand, trees from the fast-growing progenies had a smaller grain angle than the QCI control. While fast-growing progenies had lower wood density than the control, this was not significantly different. These findings suggest that, in general, the criteria used to select Sitka spruce trees in the forest as potential candidates for the breeding population would indeed lead to significant improvements of the growth performance and grain angle from improved planting stock. Breeders need to be aware, however, of possible negative influences of such selection criteria on other stem and wood properties known to influence wood strength.

The development of a mixed-species irregular stand in the latter stages of transformation was examined. Transformation of the stand, located in Faskally Forest, Scotland, began over 60 years ago and it is now managed under the selection system. The aim was to determine whether a sustainable irregular state has been reached based on a stable diameter distribution, basal area and stand increment and on whether sufficient regeneration of the desired species and recruitment into the canopy is present to maintain the distribution. Complete inventories at 6-year intervals were carried out in a 1-ha permanent sample plot established in 1997. Results from the 2009 inventory suggest that the stand has not reached a sustainable irregular condition based on the above criteria. A reduction in canopy tree number in the last harvesting intervention has slightly flattened the diameter distribution (q = 1.4 cf. 1.5 and 1.6 in 2003 and 1997 inventories, respectively). The reduction in overhead cover has increased the number of regenerating seedlings in the understorey and suggests that the stand is moving towards a more balanced structure. Shade-tolerant western hemlock and beech dominate the understorey followed by semi-shade-tolerant Douglas-fir and Norway spruce. Recommendations for future management are discussed.