Landscape-scale conservation strategies are increasingly proposed to combat the effects of habitat loss and fragmentation. These appealing strategies are based on sound ecological principles and have been widely embraced by the conservation community. However, the empirical evidence is limited and equivocal, and there is debate on the relative merit of, and balance between, site- and landscape-level actions. There is also uncertainty regarding whether the ecological consequences of removing natural land cover (i.e. fragmentation) and the benefits of putting it back (i.e. restoration) are reciprocal, further complicating decisions around when and where to focus restoration efforts.
A greater use of experimental approaches could clearly help to resolve this situation, increasing the chances of teasing apart the relative influence of alternative conservation actions. Although the importance of experimentation to advance ecology and inform conservation is widely acknowledged, these types of studies are rarely carried out over large extents. There are two fundamental challenges to large-scale experimentation in ecology. The first is based on the trade-off between the spatial scale necessary to ensure ecological realism, enabling the collection of evidence applicable to practical conservation, and the ability to exert experimental control and replication. The second is related to temporal scale, given the time it may take for biodiversity to respond to change, coupled with the difficulty and cost of running long-terms experiments and the urgency for evidence.
Natural experiments have been proposed as a way to potentially overcome these challenges as they attempt to overlay an experimental design on an ecosystem where change or active manipulation has occurred or is planned, beyond the control of the researcher. As such, natural experiments fall between true manipulative experiments and the more common, but less rigorous, correlative or observational studies. We describe how we developed the WrEN (Woodland Creation & Ecological Networks http://www.wren-project.com) project to utilise the significant changes in lowland landscapes in the UK as basis for a long-term, large-scale natural experiment. The project, which is based on 160 years of woodland restoration in UK lowland landscapes, attempts to overcome the challenges and inform future restoration by: 1. investigating the effects of habitat restoration and creation, rather than habitat removal and fragmentation; 2. studying real landscapes at spatial scales that are sufficiently large to ensure ecological realism and the applicability of evidence; 3. incorporating appropriately long time scales to account for lag effects; 4. sampling a wide range of explanatory site- and landscape-level variables; 5. examining a wide range of species. We conclude with a few insights into the emerging evidence from WrEN and possible implications for future conservation and restoration in the UK and beyond.
