The evidence for the effects on woodland biodiversity of differing lengths of forestry crop rotations and stand ages is explored and discussed in a new Research Note published by the Forestry Commission.
Entitled “Biodiversity and rotation length: economic models and ecological evidence”, the Research Note is intended to support forest planners and researchers.
It reports on a study exploring the links between biodiversity and stand age with a view to including it in stand-level models for optimal rotation lengths, and associated forest management tools. The investigation was conducted through literature reviews and re-examination of UK Biodiversity Assessment Plan (UK BAP) data.
Overall, it found limited published ecological evidence to link biodiversity to stand age, or economic modelling to account for such a link.
It revealed no simple or universal response of biodiversity to stand age. However, there was more evidence of biodiversity increasing with stand age than falling. There was also evidence that after a brief initial increase, bird and mammal biodiversity declines until the stand is about 20 years old, and increases again thereafter.
Upland Sitka spruce stands were an exception, where biodiversity levels were higher in young forests and more-mature forests, and at a minimum when the forests were about 40 years old.
The authors explain that biodiversity is a major focus of international environmental policy and practice. It is widely recognised that biodiversity in woodlands varies across different bio-geographical zones and depends upon the tree species mix, forest management approach and stand structure.
Although biodiversity value is sometimes particularly ascribed to mature old-growth forests, the relationship between stand age and biodiversity can be complex, because some species may thrive when trees are younger, or before canopy closure.
Furthermore, the relationship with stand age can also be influenced by geographical location (e.g. related to limits in the range of particular species, or soil quality), land-use history (e.g. continuity of woodland presence), tree species present, origin of the forest stand (natural regeneration versus planted) and climate change impacts.
The authors were Nadia Barsoum, Robin Gill, Laura Henderson, Andrew Peace, Chris Quine, Vadim Saraev and Gregory Valatin of the Forestry Commission’s Forest Research agency.
It is an unpriced publication available to download from the on-line publications catalogue at www.forestry.gov.uk/publications. The stock code is FCRN022.