Alternative models for productive upland forestryModel 2: Sitka spruce mixtures with alternative conifers

摘要

Upland forestry in Britain is currently dominated by two management models - (a) even-aged medium-rotation plantations of predominantly Sitka spruce (Picea sitchensis [Bong.] Carr.) and (b) conservation or ecological restoration of native woodland with minimal production outputs. To meet emerging objectives and address current challenges to sustainable operation, a wider range of upland forestry management models should be considered. Emerging objectives include mitigation of climate change by enhanced carbon sequestration and increased production of woodfuel biomass, alongside ecological restoration and enhanced rural development forestry benefits. Key challenges include impacts of predicted climate change, incidence of novel pests and diseases inexisting stands and the need to ensure a sustainable long-term relationship between forest productivity and site, soil and freshwater resources. Deployment of mixed-species stands comprising Sitka spruce and one or more alternative productive conifers, potentially capable of completing the rotation, offers the opportunity to enhance inherent stand resilience while retaining the option of a final crop of the species that is currently preferred by many processors. A recent scoping study has evaluated theprincipal advantages and challenges associated with this alternative model, considering Norway spruce (Picea abies L.), Douglas fir (Pseudotsuga menziesii [Mirb.] Franco), western hemlock (Tsuga heterophylla [Raf.] Sarg.), silver firs (Abies spp.) and western red cedar (Thujaplicata Don ex D. Don) as the most likely "companion conifers" to Sitka spruce. Key requirements for research and development are discussed, which would be essential to support wider and more confident operational adoption.