This paper looks at pragmatic ways to increase biodiversity and resilience in plantations of the UK’s most common tree, Sitka spruce. The UK Forestry Standard now guides plantations to have no more than 65% of one species, so this review asks what would work best as secondary species in Sika-dominated plantations. This means striking a balance between (i) supporting biodiversity already associated with Sitka spruce (that might decline), (ii) supporting biodiversity not supported by Sitka spruce, and (iii) ecosystem functioning. They considered 34 tree species which could feasibly be grown alongside Sitka spruce as secondary species, ether in intimate mixes or close by but in separate coupes. Native oak species, sycamore, Scots pine, native birch, beech and Norway spruce were found to provide the greatest biodiversity benefits. The analysis also found that diversification via use of ‘blocky mixes’ i.e. blocks of single species of at least 0.2 ha (0.5 acres) would work best for providing biodiversity benefits while supporting timber production. However, more research is needed into what spatial layouts would provide optimum benefits. The study notes that that diversification with broadleaved trees may result in faster nutrient cycling and litter decomposition with potential implications for carbon storage.

Reference: Ruth J Mitchell, Steve D Albon, Paul E Bellamy, Clare Cameron, Chris J Ellis, Nick G Hodgetts, Caitlyn Johnstone, Jenni A Stockan, Andy F S Taylor, Sprucing up the UK’s Sitka spruce (Picea sitchensis) forests: can tree species diversification benefit biodiversity?, Forestry: An International Journal of Forest Research, 2025;, cpaf040, https://doi.org/10.1093/forestry/cpaf040