Sandra Díaz

Sandra Díaz (Bell Ville, Argentina, 1961) obtained her PhD from the Universidad Nacional de Córdoba (UNC), Argentina in 1984. In 1993, she joined the Instituto Multidisciplinario de Biología Vegetal (IMBIV), a joint center of the Argentine National Research Council (CONICET) and the Universidad Nacional de Córdoba, where she has risen to the top academic rank of Investigador Superior. She is also Professor of Community and Ecosystem Ecology at UNC, as well as holding a visiting professorship in the School of Geography and the Environment at the University of Oxford, and heading the international initiative Núcleo DiverSus on Diversity and Sustainability. Author of almost 200 scientific publications and nine books and reports, she is Associate Editor of Proceedings of the Royal Society B, and sits on the Board of Reviewing Editors of Science and the editorial boards of other scholarly journals. She has served in leading positions in international projects including the Intergovernmental Panel on Climate Change (IPCC), the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES) and the UN’s Millennium Ecosystem Assessment. In 2019, the magazine Nature chose her for the “Nature’s 10” list of the people who helped shape science in that year.

Independently and collaboratively, the awardees focused their research on arranging each plant’s ecosystem function along dimensions of measurable physical traits, such as height, leaf type or seed size, enabling them to locate patterns in the functional diversity of species at a global level. The catalogue of these functional traits has now become a vast database, added to and used by researchers around the world for such purposes as modelling the impact of global change on ecosystems, and identifying mitigation measures.

“The increasingly massive and coordinated trait databases that have been developed [on plant functional traits] are fundamentally changing our ability to predict the consequences of climate change for both the diversity and the function of our ecosystems,” in the words of the award committee appointed jointly by the BBVA Foundation and the Spanish National Research Council (CSIC). The “trait ecology” that the co-laureates championed “is improving the design and efficacy of both biodiversity conservation efforts and predictive ecosystem models and theory.”

Díaz, Lavorel and Westoby, the citation concludes, have made “outstanding efforts to describe and sustain the complexity of life on Earth.”

Form as function

Not all plants can convert sunlight into organic matter with the same efficiency, or reproduce themselves as quickly, or consume the same quantity of water. These different abilities depend on measurable physical traits, and have a major impact on overall ecosystem functioning. This concept of functional biodiversity was already “in the air” by the 1990s, recalls Sandra Díaz in a video interview after hearing of the award. Yet it was not until the new millennium that its study got systematically under way.

Díaz herself wrote in a paper published in 2001: “There is a growing consensus that functional diversity, or the value and range of species traits, rather than species numbers per se, strongly determines ecosystem functioning. But despite its importance, functional diversity has been studied in relatively few cases.”

By then, the three had met at various international conferences, each traveling from a distinct corner of the globe. “We really connected,” says Díaz, “and had a great time talking together about the relationship between biodiversity and function.” It was from these conversations that the idea took shape to create a global database of shared knowledge, something “quite rare at the time in this field of research,” remarked Sandra Lavorel, speaking from New Zealand, where she is currently on a research stay at the Landcare Research Center in Lincoln. The three explained the project to their initially reticent colleagues, who decided to sign up, says Díaz, “basically because they trusted us.”

This was how they came to play what the committee calls “critical roles in formalizing the study of plant traits, inspiring their colleagues across the planet to share in the effort to measure the functional diversity of plants within and across ecosystems.”

A database of 200,000 plant species

The success of the initiative exceeded all expectations. At the time of writing, the TRY database – its name a nod to the hard task they knew would lie ahead – contains 12 million entries, documenting the functional trait diversity of some 200,000 plant species.

The committee was at pains to stress the value of this tool, stating that “trait ecology has allowed ecologists to make common and standardized measurements of plant function in every ecosystem on Earth.”

Plants perform vital ecosystem functions, like carbon fixation, nutrient acquisition and the accumulation of living biomass. Now, thanks to the TRY database, researchers can project how efficient a plant will be at these or other tasks on the basis of its physical traits.

A milestone in their collaboration was the 2016 paper “The global spectrum of plant form and function,” published in Nature, which marked the first attempt to classify functional biodiversity by reference to six physical traits. These traits have to do primarily with the size of plants and their components, such as seeds, and the workings of the “leaf economy.” Westoby elaborates on this last concept, explaining that “some leaves capture light very ‘cheaply’, that is, capturing a lot of light for the level of resources they invest, but at the cost of being relatively short-lived. At the other end of the spectrum you have relatively ‘expensive’ leaves with a low rate of return, but that last for a long time.”

For Díaz, the great global catalogue of forms and functions set out in 2016 is “the first snapshot of the functional diversity of the Earth’s vascular plants.” Behind it is the ambition to understand the mechanisms that drive the functioning of each ecosystem. Westoby continues with the analogy: “Ecosystems are a machine where the cogs and the levers and the connecting rods are species. And so being able to understand how those pieces of machinery work is a prerequisite for being able to forecast the consequences of any kind of change in the environment, including those due to stressors of human origin.”

Mounting a better response to climate change

The kind of knowledge provided by the functional approach, and a database like TRY, is already being applied in the design of models to improve ecosystem adaptation to climate change. Lavorel explains that it has been shown, for instance, that slower growing plants are more resistant to drought, a phenomenon set to increase with global warming in regions like the Mediterranean. But at the same time, slower growing crops capture less carbon, so it is important to factor both variables into future adaptation plans.

Another research strand is the relationship between plants’ functional traits and the production of foods. And one of the connecting threads is pollination: “A large proportion of the world’s crops are pollinated by insects,” says Lavorel, “and the traits of the flowers of these plants determine which insects will be able to pollinate them, which will ultimately influence their levels of production.”

In short, understanding each plant’s function allows to model how the ecosystem will change in response to environmental changes, providing a key input to conservation planning. “Species are not disappearing randomly,” says Díaz. “Some organisms are systematically more affected than others, because they have traits that make them differentially vulnerable. Our work helps generalize which are those vulnerable organisms, and what we lose in terms of ecosystem properties and benefits to people when those species disappear. In this sense, what we do highlights how inextricable are our connections with the rest of living nature.”

The need to act urgently

Asked about today’s dramatic rates of biodiversity loss, the co-laureates concur in the necessity of urgent action. “What is at threat is the functioning of the tapestry of life on Earth, of which we all form part, and we cannot expect a reasonable future without it,” Díaz warns. “It is not too late to act, but the window of opportunity is rapidly closing. What we do in the next few decades will be decisive.”

Westoby, for his part, sees species as a precious legacy of the evolution of life on our planet which we must fight to preserve: “On average a species will have a million years of history; through all that time, each one has been solving problems that are somehow unique to it, so when you lose species it’s like burning libraries or bulldozing important monuments. It’s all of those things, only I would say more severe, because we’re talking about the deep history of life on Earth. And we stand to lose really large proportions of species over the next 100 years.”

Sandra Lavorel too likens biodiversity to “a library of life” that has come gravely under threat before we have even fully understood it: “We all know now that it is absolutely urgent that we reverse the current trend if we don’t want to sink the boat that is our current Noah’s Ark.”