In 2024, Proceedings B decided to extend its review portfolio further by introducing a new commissioned review in conservation biology. The aim of the “Georgina Mace review” is to annually showcase current topics and progress in conservation biology, which will be of general interest to the diverse readership of Proceedings B and is of relevance to policy makers and those tasked with the stewardship of natural resources. E.J. Milner-Gulland was invited to write the first review and, along with her co-authors, tells us more about their paper.
Professor Dame Georgina Mace was a titan of conservation science. Evidence of her legacy can be seen in the IUCN Red List, the Millenium Ecosystem Assessment and the phrasing of the Global Biodiversity Framework. Georgina’s work was honoured through a multitude of awards and prizes, but she is also remembered as an exceptionally kind and supportive mentor, especially to early career researchers. Two members of our authorship team (EJ and Julia) were among the many lucky ones for whom Georgina was a role model and a kind supporter. It has been such a privilege to commemorate her scientific contributions through writing the inaugural Georgina Mace review.
Our paper tackles a fundamental question: How can the complexity of nature be reduced to one metric, which can be used to assess changes in biodiversity and attribute these changes to conservation action? Many actors increasingly seek to quantify their biodiversity impacts, particularly to participate in emerging biodiversity markets where credits (quantifiable units of biodiversity improvement) are to be traded. These new markets beg the question of what a "credit" represents. What does it mean to abstract biodiversity, in all its vast complexity, to a single number? What are the potential benefits, and harms? These are all questions upon which Georgina would have had an opinion, and her presence was in our minds as we wrote this piece.
We arrived upon this topic for the review from a fortuitous confluence of ideas. In January, Sophus and Hannah had a conversation about the questions the emerging credits market raised about measuring biodiversity. EJ, Harrison and Henrike were added to the team, and we planned a more specific project stress-testing different means of defining units of nature. However, we realised that we were first lacking a common language with which to discuss the approaches being taken. We sought a summary that would give the lay of the land, but it didn’t exist, so we decided to write it ourselves.
Around the same time, EJ was approached by the Proceedings B team to write the inaugural Georgina Mace review. She suggested the topic of whether there could be "one true metric" for biodiversity; something she had been thinking about and presenting on over the previous few months. However, she was lacking an empirical core around which to frame a paper. Given the honour and burden of the Georgina Mace review, she wasn’t sure how to move forward.
Whilst EJ alone, and our group together, were separately pondering our dilemmas, the European Congress on Conservation Biology was held in Bologna, Italy. EJ and Hannah's long-term friend and colleague Julia was there, and through a series of conversations she pointed out the obvious convergence of our separate projects. A late-night, prosecco-fuelled discussion followed, during which the title emerged: “What is a Unit of Nature?”. Simple, pithy, perfect. This is where conferences, where you can indulge in free-form discussion and share intellectual excitement about ideas in social contexts, are so valuable.
We tested many versions of the framework over the coming months. We faced the classic problem that any taxonomist faces; striking the balance between lumping and splitting, ensuring the framework was general enough to be understandable, but specific enough to cover the variety of approaches being taken. We had a last-minute veer into framing the whole thing around different types of uncertainty, before these elements were consigned to the "graveyard of the uncertainties", perhaps to be resurrected for a future piece.
The meat of the paper is the conceptual challenges which must be tackled when abstracting biodiversity to a single tradable unit of improvement in the state of nature. We aim to be a bridge between the academic community who understand biodiversity measurement and counterfactual impact evaluation, but perhaps are less familiar with the rapidly evolving biodiversity credit market, and those in industry who don’t usually read the academic literature. We situate the specific topic of biodiversity credits into a longer tradition of implementing market-based mechanisms for biodiversity conservation and evaluating the impact of interventions on biodiversity outcomes.
This was one of the most fun, intellectually stimulating and energising papers that we have been involved in. We debated, reframed, deconstructed and rebuilt our arguments, but all within a warm, encouraging, and supportive team. One topic of debate was how strong a position the piece should take. At the beginning of the writing process, our viewpoints spanned all axes of thought on credits, and on the interaction between capitalism and conservation. But in the end, we came to consensus about the message we wanted to send. If you would like to know what that is, do read the paper!
We hope you enjoy reading it as much as we enjoyed writing it. We also hope that, in both subject manner and approach, this work has done Georgina justice.
About the Authors
Hannah Wauchope is a Lecturer in Ecology and Conservation at the University of Edinburgh. She is interested in how we measure biodiversity and make inferences from imperfect data, with a view to understanding the impact of conservation interventions and tracking progress towards policy targets.
Sophus zu Ermgassen is a Postdoctoral Researcher at the Nature-positive Hub and the Leverhulme Centre for Nature Recovery, University of Oxford. He specialises in biodiversity finance, nature-positive organisations, infrastructure sustainability, sustainable finance, biodiversity offsetting and ecological economics.
Julia P. G. Jones is a Professor in Conservation Science at Bangor University and Prince Bernhard Chair in International Nature Conservation at Utrecht University. She is particularly interested in causal inference to evaluate the impacts of conservation on both people and nature, to make conservation more effective and equitable.
Henrike Schulte to Bühne is a Postdoctoral Research Associate at the Institute of Zoology, Zoological Society of London. She is interested in using satellite remote sensing data to understand human impacts on ecosystems at the landscape scale, including how threats interact.
Harrison Carter is a DPhil student within the Wildlife Conservation Research Unit and Interdisciplinary Centre for Conservation Science at the University of Oxford. His work focuses on human-wildlife coexistence, and the impacts of novel financing mechanisms (such as credits) on conservation efforts in Sub-Saharan east Africa.
E.J. Milner-Gulland is the Tasso Leventis Professor of Biodiversity at the University of Oxford. She is interested in understanding how social, ecological and behavioural factors interact to affect key issues in conservation, and in improving the effectiveness of conservation interventions.
Read the paper: What is a unit of nature? Measurement challenges in the emerging biodiversity credit market
Proceedings B is looking to publish more high-quality research articles and reviews in conservation biology. If you have an idea for a review, we strongly encourage you to submit a proposal by completing our proposal template and sending it to the journal. More information about the journal and the submission process can be found on our website.
Images: Georgina Mace by Jussi Puikkonen
