Understanding the relationships between crop diversity and food security

At the interface between agroecology and ethnoecology, the ASSET (AgrobiodiverSity for a food-Secure planet) project was selected as part of the MOPGA (Make our Planet Great Again) international call launched in 2018 under PIA - France 2030. It focuses on the resilience of agroecosystems when dealing with extreme climate events. In the five years since the project was launched, four sites in France, Morocco, and Senegal were used as privileged observation posts, both locally and nationally, to assess the benefits of agrobiodiversity on crop yields. An interview with Delphine Renard, CNRS researcher and project coordinator.

How did the project come about and what were the challenges that led to its creation?

Delphine Renard: The ASSET project¹ addresses the impact on agriculture of extreme climate events, which are by nature both unforeseeable and destabilising for agricultural production. In the future, these extreme climate events will become more frequent and intense. In 2018, when the project began, we were beginning to better understand the effects of these extreme climate events on agriculture, but efforts focused more on the longer-term impact of climate change on crop yields.

ASSET grew out of an initial study published in Nature in 2019. By using FAO statistical data, I demonstrated, on a national basis and over a period of five decades, that the greater the crop diversity in a particular country, the more stable its food production over time.

The three main objectives of ASSET were to get a better sense of what lay behind this statistical link. The research sought to test whether agricultural biodiversity, particularly that of crops, could help stabilise crop yields and develop more resilient agriculture in the event of extreme climate events.

How did it work, in practical terms?

Two disciplines were at the interface of this problem: agroecology, which applies ecology to agricultural issues, and ethnoecology, which assesses the relationships between societies and their environment.

The project focused on droughts, but we also worked on grapevines in France, impacted by late frost and hail. We conducted our research in four specific locations. In France, we focused on the Tarn region of Gaillac, using a “vine” model, and on the Trièves region (Vercors), with its many varieties of barley used for local whisky production. In Morocco, we are working according to a “polyculture: olive trees, cereals, legumes” model, and in Senegal on a “cereals and legumes” model. 

What objectives and methods were used? What were the main results?

The first objective was to better understand the mechanisms through which diversity leads to steadier production, at diverse spatial scales. The methodology was based on statistical and mathematical modelling using FAO  and simulation data. We also implemented two field observatories for long-term monitoring at the smallest scale, that of the household. To measure stability, we need data that can be tracked over time, but they are never collected on the overall basket of species or varieties grown. We are trying to fill this gap.

Locally, we are measuring productivity on four vine varieties in the Gaillac region, and on 6 species/17 varieties grown at our 3 sites in Senegal. This year, we are conducting our 4^th data collection in France, and our 5th in Senegal. The yield data acquired for each species/variety will help us test diversity-stability connections, as well as identify plant combinations that promote greater stability in agricultural production. We will be able to answer this question once the data collection is complete².

Through mathematical modelling, we were able to compare the benefits of agricultural diversification on the regulation of two wheat pathogens, using different practices (rotation, mixtures of species/varieties), doing so from the level of the plot to that of the landscape, and under various climate conditions. An article was published in Landscape Ecology.

Finally, the objective was to better decipher how and why farmers choose a diversity of plants in the field. For instance, in Senegal we found that farmers combine a great diversity of species and varieties within the same plot (37 different forms of association), and that these combinations are not, at first glance, those recommended by agronomists. From an ethnoecological perspective, through interviews and an analysis of literature³, we sought to understand what motivates farmers to make these combinations, and how they mobilise local knowledge to address climate constraints. More broadly, we are interested in the socio-cultural, scenic, medicinal, gustatory, agronomic, and ecological values associated with the diversity of these plants. All these values coexist, and are not at all separate in the minds of farmers.

From an agroecological perspective, how can we explain the role agrobiodiversity plays in stabilising agricultural food production?

Our approach is based on a simple mechanism, known as “insurance”, in connection with the unpredictability of these extreme climate events. To put it simply, this would be a phenomenon akin to the saying: “don't put all your eggs in one basket”. Sowing a variety of plants with different responses to various climate events, or with more or less sensitivity to stress from pests or diseases, can make harvesting more secure through a compensatory effect. Depending on the year and the weather, a species will flourish to a much greater extent compared to another, and the overall production will remain “stable on average” over time. Our results show that this process is at play, especially on the national level, and could complement the stabilising effect of irrigation, mainly used for field crops.