Offsetting and uncertainty

Following the release of the Biodiversity Offsetting Green paper last month, the BES invited ecologists and offsetting practitioners to attend a workshop in London.  The aim was to discuss the science of offsetting and identify knowledge gaps that will need addressing if offsetting is to be effectively implemented in an ecologically sound way. During the workshop, one topic which continued to surface was the degree of unpredictability surrounding the creation and restoration of habitats and the associated challenge of developing legislation for delivering such offsets. Namely, if the success of an offset is measured by the arrival at a particular end point, how does the policy account for the creation of habitats which miss their targets but still possesses legitimate ecological value?

When ecosystems and habitats are created there are controlling factors such as site characteristics, landscape context and site history which influence the type of resulting habitat. However,  there are also random factors which can determine the eventual species richness, abundance and community composition of the habitat. It could be argued that these chance elements, for example species introductions, are important for the creation of unique habitats. Indeed, it is possible that situations may arise whereby chance occurrences lead to a newly created or restored site being more ecologically valuable than its intended target end point. Equally, however, it is also possible that these random events could be detrimental to the fledgling habitat.

Some attendees of the workshop argued that the success of an offset should therefore not be measured by the arrival at a particular end point, but through the implementation of a specific set of actions designed to deliver a particular habitat. Others believed that any truly robust legislation would require benchmarks and targets to ensure full commitment from developers. This uncontrollability of outcome could potentially affect any offsetting policy, as looser restriction on what constitutes a successful offset may depend upon individual interpretations of “success”.

If a developer is legally obliged to deliver a well-defined set of offset outcomes, the science behind habitat creation therefore needs to minimise the impact of chance. In order to do this, it would be necessary to know if a certain type of habitat could be created through the application of a step-wise set of input parameters, ensuring a level of biodiversity is maintained.

A study published in the latest edition of the Journal of Applied Ecology looks at just this. While not in the context of biodiversity offsetting per se; Emily Grman, Tyler Bassett and Lars Brudvig attempt to answer the question, “do managers control the drivers that are most important in shaping restoration outcomes, or can they only fine-tune communities that are predominately shaped by factors outside management control?” Their paper looked at the relative importance of particular factors in the establishment of plant community outcomes across 27 prairie restorations in south-west Michigan. By focusing on diversity and composition in relation to management, landscape and historical factors, they were able to determine which factors most influenced the outcomes of restoration. Across the sites they found that for the most part it was in fact management decisions which tended to play a more significant role in determining outcomes than previous site condition or landscape context, specifically what habitats surround the restoration site.

While their findings may bode well for prairie restoration projects, the researchers comment that, to their knowledge, this is the first study of its kind. It would be critical to determine if this data holds in other habitats before suggesting that a successful restoration can be delivered through management alone. Research in this area may help to develop a more predictive framework for achieving restoration outcomes, but when dealing with nature there will always be an unpredictable element.

The lack of comparative data on delivery of restoration projects highlights that there is scope for developing a broader and more robust evidence base to biodiversity offsetting, both through further research and collation of existing datasets.