British woodlands today provide a variety of ecosystem services, from carbon sequestration for climate change mitigation all the way to recreation and flood prevention. Given that the country only has 13% woodland cover, there is a pronounced drive for woodland cover increase; 30,000 ha and more annual woodland creation are planned until 2050, not least to meet the UK government’s Net Zero targets. While Britain has over 100 years’ worth of experience with woodland creation already, realised woodland creation in recent years has significantly fallen short of its targets. The British landscape is a cultural and crowded landscape, where most every piece of land already serves a range of land covers and land uses; integrating many thousand hectares of new (often native broadleaf) woodland into this complex landscape is difficult, as it may elicit undesirable trade-offs. As one potential solution, natural colonisation, i.e. the colonisation of trees on previously non-wooded land, is being introduced as a cheap and easy way to create structurally diverse woodlands (especially compared to active planting). Championed by the rewilding movement, natural colonisation is a relatively new approach to expanding woodlands and knowledge on its extent and how much it can really contribute to Britain’s woodland expansion plans is limited to non-existent.
This thesis explored emerging opportunities for native woodland expansion in these crowded future landscapes to help shed light on potential ways forward. In doing so, it analysed historic drivers of woodland expansion in Britain, including afforestation targets and realised afforestation, to understand legacies of forestry history and valuable lessons to learn for the future. It also focussed on the approach of natural colonisation by using a landscape-scale case study area in North Wales as a basis for an investigation of existing spatial data and observational site visits, as well as a grounded theory approach and semi-structured interviews with farmers and other land managers on the extent and potential of natural colonisation in creating new native woodlands.
A key finding of this research is that woodlands today must provide more (diverse) benefits than ever before and must do so in a time with more competing interests than ever. Furthermore, this increased complexity is the main reason why realised afforestation has been falling short (compared to the targets) since the 1980s, and an overreliance on woodland creation targets remains ill-advised until there is a clear plan on what trade-offs will be accepted on a national, regional, and local level in the pursuit of native woodland expansion. Such considerations must also include a revision of the metrics used for these woodland expansion
targets, as the amount of land covered in trees has no linear relationship anymore with the provision of those ecosystem services new woodlands will be created for.
What the complexity of woodland expansion drivers also did, however, is offer new possibilities of creating native woodlands, specifically via natural colonisation. Unlike what might have been the case in the 20th century, natural colonisation can now provide a range of benefits 21st century woodland expansion in Britain is looking for. A key finding of this research is that natural colonisation can unlock areas of woodland expansion where active planting is not suitable; more so, unintended natural colonisation is able to circumvent land management barriers that hinder other options of woodland expansion. Natural colonisation cannot yet be found on any available spatial datasets on tree cover, but recent natural colonisation already exists, and a lot of it matches areas identified as woodland expansion opportunities.
Overall, natural colonisation should be emancipated as an equal and valid approach to 21st century native woodland expansion. It is an embrace of the crowdedness of the British landscape and its drivers, where no one ‘perfect’ woodland fits all, but the more options available for expanding woodlands, the more likely the targets and plans, whichever way they will look like, can be achieved.