An analysis of conifer experiments in Britain to identify productive alternatives to Sitka spruce

Abstract

Abstract As the climate changes there is a need to reduce the reliance on Sitka spruce (Picea sitchensis (Bong) Carr.) in upland British forestry and increase species diversity to lower the risk of damage or loss of production due to biotic or abiotic events. An analysis of relevant species trials was carried out to assess the productivity of potential alternative conifer species on upland site types in Britain. Data from 87 forest experiments planted between 1929 and 1995 were analysed to compare long-term performance of 52 species with that of Sitka spruce under the same conditions and site type. Sites were broadly categorized using soil and climatic factors, which were used as primary factors in models predicting General Yield Class (GYC, the maximum mean annual increment in m3 ha−1 year−1) of the potential alternative species and of Sitka spruce. No species had significantly higher GYC estimates than Sitka spruce, but grand fir (Abies grandis (Douglas ex D. Don) Lindl.), noble fir (Abies procera (Rehder)), western hemlock (Tsuga heterophylla (Raf.) Sarg.), Lutz’s spruce (Picea x lutzii (Little)), maritime pine (Pinus pinaster (Aiton)), Lawson cypress (Chamaecyparis lawsoniana (A. Murray bis) Parl.), Scots pine (Pinus sylvestris (L.)), Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and western red cedar (Thuja plicata (Donn ex D.Don)) all had GYC estimates which were not significantly lower than that of Sitka spruce under certain soil and climate conditions. A further 26 species, particularly Abies species, had GYC within 3 m3 ha−1 year−1 of Sitka spruce but were present on too few sites for inclusion in statistical models. The results of the analysis provide objective evidence for the planting of a wider range of species where Sitka spruce may currently be first choice. In the absence of any major pest or disease affecting Sitka spruce, it is still a good choice for many upland sites, however, a wider range of options with equivalent productivity exist, allowing forest managers to diversify and reduce the risk of damage or loss of production due to biotic or abiotic events.