Evidence review: how do woodland creation approaches give rise to differences in woodland structure?
Abstract
1. There is increasing demand to expand the extent of native woodland in the UK, to tackle both climate change and biodiversity crises. In general, there are three approaches to woodland creation - natural regeneration/colonisation, direct seeding and tree planting. However, much is uncertain about the effects of each strategy on woodland structure. This review compiles available evidence on the effects of establishment approaches on woodland structure to inform the Woodland Trust's guidance on woodland creation. 2. Natural regeneration and colonisation of woodland can be rapid but also highly variable, depending on a wide range of factors including soil quality, seed dispersal and grazing pressures. Natural regeneration can produce good seedling density and increase spatial and vertical heterogeneity when compared to planted sites. However, a key limitation is ensuring sufficient ground cover to shield out competitive vegetation, such as grasses. 3. Direct seeding allows for more control and consistency and can create a good level of seedling density. This is particularly the case if direct seeding is used in combination with cover crops or ploughing. Direct seeding can create a great variety of woodland structures but is technically challenging and may require supplemental plantings. 4. Tree planting offers the most controlled woodland creation method, with utility for specific situations where rapid results are required, specific species compositions are needed or on challenging sites. Planting easily achieves a high sapling density, but cluster planting/applied nucleation is required to achieve naturalistic canopy appearance and assist regeneration. 5. It is largely unexamined whether different woodland creation approaches deliver quality habitats. Initial establishment approaches may leave a fingerprint on new woodland, but there are other contributing factors, including management and other natural processes which determine the trajectory of woodland development and shape its structure. For the best possible outcomes, the woodland creation approach should be considered with the type of management required to achieve stated objectives and whether this is likely to take place. The relative merits of choosing one woodland creation approach over another is likely to be a question of cultural and social expectations as much as it is about effectiveness.