Reviewing the evidence base for the effects of woodland expansion on biodiversity and ecosystem services in the United Kingdom

Woodland expansion is internationally accepted as a strategy to reduce biodiversity loss, climate change and flood risk, but there has been limited assessment of the evidence for these benefits. In addition, despite UK targets for woodland creation, planting levels remain low. Furthermore, following the UK's decision to leave the European Union, a number of important decisions will be made about support mechanisms for different land uses, making evidence for the effect of woodland creation in different contexts essential. Following established guidelines, we undertook a systematic review of 160 articles to assess the evidence base for the effects of woodland expansion on ecosystem services in a UK context. We aimed to characterise the evidence base on the effects of such woodland expansion on biodiversity and ES and highlight where further research might be required. We found that the evidence base is dominated by research studying conifer plantations, and outcomes relating to biodiversity and regulating ecosystem services. By contrast, evidence for the effect of afforestation on multiple ecosystem services, cultural, and provisioning services is severely lacking. We argue that this weighting of evidence towards 'public goods' may contribute to the observed lack of planting, and that evidence for more tangible effects of woodland creation in relation other land uses is lacking. Implementation of woodland expansion could benefit from developing new incentives for planting woodlands, based on 'public money for public goods'. Future research should focus on the evidence gaps identified here, making use of context-specific, transdisciplinary, participatory methodologies which take into account plural values held in relation to the landscape.