Paul Leadley: Studying the impacts of global change on biodiversity

Paul Leadley is a professor of ecology, a lecturer at the Ecology, systematics and evolution laboratory (ESE – Université Paris-Saclay, CNRS, AgroParisTech), and coordinator of the C-BASC interdisciplinary project (Center for Interdisciplinary Studies on Biodiversity, Agroecology, Society and Climate) at Université Paris-Saclay. A specialist in biodiversity modelling and the use of scenarios to produce decision-making tools, he is the lead author of three IPBES (Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services) assessments.

Paul Leadley's story begins in his native United States. Studying biology and mathematics at Pennsylvania State University, he owes his budding interest in ecology to a friend, who was then on a postdoctoral fellowship in the field. "We did rock climbing together and often discussed ecology," recalls Paul Leadley. With his Bachelor's degree in the bag, he became interested in modelling living organisms and began a Master's degree on the effects of rising atmospheric CO₂ levels on soybeans. "Initially, I was more interested in agricultural ecosystems," explains the lecturer. After a few years working as a research engineer, in 1990 he embarked on a thesis devoted to modelling the impact of climate change on the arctic tundra at San Diego State University. He then decided to do his post-doctorate at the University of Basel, Switzerland, still working on the effects of rising atmospheric CO₂ levels on grassland ecosystems. "It was then that I became interested in the impact of global change on biodiversity," explains Paul Leadley. His research led to a position as a lecturer in plant ecology at Université Paris-Sud - now Université Paris-Saclay - in the Ecology, systematics and evolution (ESE) laboratory, which he led from 2006 to 2014 and to which he still belongs.

Biodiversity and ecosystem functioning

In the ESE laboratory, Paul Leadley conducted research into the link between biodiversity and ecosystem functioning. "This was when we were beginning to make the link between modelling work, experiments and field observations around these issues. So I applied this approach by carrying out experiments in Montpellier, California and all over the world, in which we manipulated the number of plant species and studied the impact on the functioning of the ecosystem — usually grasslands," explains the researcher. This work enabled him to demonstrate what the entire scientific community agrees on today: that a reduction in the number of plant species has a harmful effect on ecosystem functioning. "I was also very interested in the underlying mechanisms. In particular, through experiments and modelling, I studied the impact of climate change and biodiversity on the nitrogen cycle, aiming to better understand the harmful effect of biodiversity loss on ecosystem functioning," he adds. 

At the science-policy interface

While this work enabled Paul Leadley to gain international recognition relatively quickly, it also prompted him to consider how his findings could be taken into account in the political sphere. "I wondered, for example, how a scientifically proven result, such as the fact that biodiversity loss has a negative impact on ecosystem functioning, could be taken into account at an international level in political decision-making," explains Paul Leadley. He therefore got involved in international programmes organising environmental research very early on. In the early 2000s, he became coordinator of the bioDISCOVERY project launched by DIVERSITAS (an international programme on biodiversity science) and Future Earth (the new international programme for integrated global change science). 

IPBES and the CBD: Biodiversity on the international political agenda

While in the early 2010s, many of his colleagues were sceptical about the need for biodiversity expertise on a global scale, Paul Leadley was involved in setting up the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), which was finally launched in 2012. He then became a member of the Multidisciplinary Expert Panel (MEP, 2013–2018) and lead author of three IPBES assessments, including the 2019 Global Assessment of Biodiversity and Ecosystem Services and the IPBES-IPCC report on the interactions between biodiversity and the climate (2021). He is also an expert contributor to the IPCC Fifth Assessment Report (2014). 

During the same period, he also worked closely with the Convention on Biological Diversity (CBD), coordinating the 2010 report on biodiversity scenarios, then the entire technical report for the 2014 Global Biodiversity Outlook 4 and, more recently, providing scientific support for the negotiations leading up to CBD COP15. "As the years go by, I realise how difficult it is for science to influence political decision-making. For example, it's a shame that the COP15 negotiations failed to establish a quantified target for carbon storage by natural ecosystems — even though this has been scientifically documented. I am delighted, however, that our work has helped many countries to approve the target of a 50% reduction in pesticide-related risks," explains Paul Leadley. 

C-BASC: Towards the implementation of ecological transitions

Paul Leadley is not turning his back on work at a local level given that he's now involved as an expert on an international stage — quite the contrary. He is a co-coordinator of the Center for Interdisciplinary Studies on Biodiversity, Agroecology, Society and Climate (C-BASC) - whose mission is to contribute to the study, design and implementation of the ecological and agroecological transitions at a territorial level through interdisciplinary research, training and innovation. The Plateau de Saclay and surrounding area is a particular focal point for the C-BASC project. "We work closely with several local stakeholders - farmers, local councillors, and organisations such as Terre et Cité in particular - on how to implement ecological and agroecological transitions at a local level. For example, we're thinking about setting up a Living Lab on the Plateau de Saclay. It's a fascinating job, which allows us to see the strong links to what's being decided at an international level, but also to recognise what is sometimes a huge gap between international objectives and the reality of implementing these objectives on the ground," says Paul Leadley. Is this a reason to despair? "No. There are so many local initiatives around today in terms of the organic sector and short supply chains, for example," the lecturer responds. And to conclude: "As for the systemic obstacles linked to the complexity of the interface between technological, industrial and economic issues, I believe that we can only overcome them by adopting an approach that is both interdisciplinary and involves several different stakeholders — an approach that we are trying to bring to life within C-BASC."