Long-term floodplain meadows cannot realistically be recreated!

Biodiversity offsets are making headlines as a new instrument or tool for biodiversity conservation in the UK. DEFRA defines offsets as actions in favour of biodiversity that are carried-out in compensation for planned impacts (e.g. from development) and provide a measurable outcome. Whenever possible, offsets should target the same biodiversity components (species, habitat types etc.) as those that will be impacted. This raises the question of their “restorability”.

In a recent paper published in the Journal of Applied Ecology, Ben Woodcock, Alison McDonald and Richard Pywell of CEH investigate the restorability of long-term floodplain meadows on agricultural land in South-Eastern England. Using an 22 years old restoration experiment, they show that given the current restoration trajectory, it would take over 150 years for the former arable land to have a species composition close to that of long-term floodplain grasslands. Even when being less restrictive in terms of restoration goals, i.e. focusing on the “types” of species (described using their morphological and reproductive characteristics or “traits”), it would take over 70 years. This is slightly more realistic but still a very long term prospect.

Ecosystems or habitat types for which restoration is a (very) long-term endeavour might fall outside the scope of offset schemes. As the authors say:

any compensation scheme proclaiming they can replace floodplain meadows lost to development (i.e. gravel extraction) is being wholly unrealistic.

As well as actually avoiding the destruction of hard or impossible to replace ecosystems and habitat types, these findings raise two issues:

  • can the destruction of these habitats be offset by restoring or enhancing degraded habitats (of the same type). This amounts to exchanging area (for which there will be a net loss) by quality (for which there would be no net loss). Is this acceptable? Another option considered by DEFRA is to use out-of-kind offsets.
  • how can the delays associated with restoration or enhancement of habitat types be taken into account in the design and sizing of biodiversity offsets. DEFRA proposes to use “multipliers” for this but these will probably be very hard to justify, ecologically, as ensuring that offsets lead to no-net-loss of the particular target habitat type.
  • Hopefully, the pilot scheme launched by the UK government will give the opportunity to test these solutions…

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