Evidence review: what are the effects of active interventions on biodiversity in newly established woodlands?
Abstract
1. Newly created and young woodlands often lack important attributes that contribute to a well-functioning woodland ecosystem. Active management can accelerate the development of these attributes to attain high conservation-value woodlands more quickly. To achieve the most effective outcomes, it is important to understand the effects of management interventions on biodiversity. A range of intervention approaches are investigated here, through a review of scientific and grey literature and expert experience. 2. Artificial structures for cavity-dependent species: Nest boxes can have desirable effects on bird populations and fecundity, especially if well-designed and placed in suitable locations at a range of orientations. The benefits for bats are more equivocal. Boxes for saproxylic invertebrates can provide alternative habitat, but only when placed near existing old hollow trees with source populations. 3. Veteranisation: Anecdotal evidence shows that insects, birds and bats utilise chainsaw-carved holes soon after creation. Pollarding and ring-barking accelerate the formation of decaying wood for saproxylic invertebrates or other excavating species such as woodpeckers. These techniques are appropriate for recently planted woodlands as they rapidly create structural diversity and a variety of deadwood. 4. Species reintroduction, population reinforcement and assisted colonisation: Species reintroductions can restore ecological functioning and bolster populations of rare species (e.g. black poplar). Assisted colonisation is less widely practiced or well understood but may be used to introduce woodland plants, fungi or lichens to woodlands that are isolated from other woods and/or are established on agricultural land. 5. Increasing structural complexity: Young woodlands have a high density of even aged trees. Selective thinning, coppicing and pollarding are ways of introducing heterogeneity to the woodland understory. The conservation objectives must be clear from the outset, as this affects which technique is appropriate and practical. The biodiversity value of a woodland can be further enhanced by creating open small areas through linear rides and glades, and by re-sculpting woodland margins. 6. Grazing: Grazing by large herbivores can help maintain open areas in woodlands, create structural complexity and enhance floral diversity. Considerations include forage quantity and quality; densities of wild herbivores and habitat use patterns. The right levels of herbivory will ensure the maintenance of earlier successional stages, but grazing can also hinder the successful recruitment of trees and shrubs and negatively impact other species. 7. Recommendations for future research: Evidence gaps were identified where research at present is inconclusive, lacking for the UK, or a major gap exists in the literature.