For the latest post in our Functional traits in agroecology series, Stephen Wood (The Nature Conservancy, Yale School of Forestry & Environmental Studies) highlights the importance of considering social and human, as well as ecological traits in agricultural systems. The full article, Nutritional functional trait diversity of crops in south-eastern Senegal is a part of a Special Feature in Journal of Applied Ecology.

Crop yields have risen dramatically since the mid-20^th century, but human malnutrition is still a major global problem. Solutions are needed to feed the world well, while also maintaining a healthy environment.

A long trend of rising crop yields is due to the adoption of technologically efficient agronomic practices associated with the Green Revolution. The upshot of this global increase in crop yields was greater ability to reduce hunger by producing more calories. Yet, crop yield—the most common metric of agricultural efficiency—is not necessarily a good proxy for the more-than-50 nutrients needed for a balanced human diet. In fact, crop nutrient production was stagnant or declining throughout the 20th century while yields increased. If the challenge of the 20^th century was to feed the world, the challenge of the 21^st century is to feed the world well.

Nutrition-related human health outcomes are the result of many complex factors, but a balanced and diverse diet is a necessary precursor to reducing malnutrition. Promoting and monitoring diverse diets is a challenge because of limited metrics. Crop yield is an enticing metric because it is a single score that is easy to interpret and design policy and practice around. Diversity —whether of diets or ecosystems — is a challenge for public policy and practice because it does not conform to the simple metrics we often rely on for decision making.

Many ecological diversity metrics capture not just the diversity of species in a system but the diversity of their functional roles. These functional trait diversity metrics represent an important understanding that different species can impact the functioning of ecosystems in different ways, depending on their properties. In an ecosystem, what influences ecosystem functioning is the diversity among species in ability to photosynthesize, acquire nutrients from soil, and other traits of species.

Analogously, nutrient content is a functional trait of crops that is important for human nutrition and can be measured using similar ecological metrics. As non-crop plants vary in their photosynthetic potential, crop plants vary in their protein, iron, folate, and vitamin A contents. Using functional trait diversity metrics my colleagues and I have shown that nutrient diversity in national food supplies can be as important to nutrition-related health outcomes as aggregate caloric availability. There is, thus, growing consensus that optimizing food systems for micro- and macro-nutrients could more effectively address hunger and undernutrition than strictly increasing total food production.

Theoretical work on ecological diversity metrics has shown that there is no single “best” ecological diversity metric, making it unclear a priori which metric(s) should be applied to nutrition. One challenge is that interpreting most ecological metrics requires nuanced understanding of the mathematical differences between metrics, which can be a barrier for an applied user. There is thus need for metrics that are easily interpretable in the lens of nutrition.

Two metrics designed to be interpretable by an applied user are nutritional yield and potential nutrient adequacy, which I developed in a recently published article in Journal of Applied Ecology. Nutritional yield is the number of people whose nutrient needs could be met per hectare, for a specific crop and nutrient combination. This metric is easily interpretable, but it is not easily applied to systems with many food items and many nutrients, since it is calculated on a per nutrient-per food item basis. Potential nutrient adequacy is a single score that can be used to describe an entire food system. The score is a combination of the magnitude of nutrient adequacy (average value across all nutrients), and the number of nutrients for which there is adequacy (fraction of nutrients potentially meeting > 100% needs). This reflects both that a population needs to meet multiple nutrients simultaneously, and that providing more nutrients can nourish more people.

Applying potential nutrient adequacy to a case study in Senegal, I show that both intensifying yields of staple crops and diversifying production to include non-staples can increase nutritional production and the potential to meet nutritional needs. Yet, a combination of intensification and diversification is needed to meet the need for a diverse group of nutrients.

Much application of functional traits to agricultural systems has focused on how agriculture impacts the environment. This is important, but insufficient because agricultural systems are social/human and ecological systems. Extending trait-based approaches to agriculture means identifying a new set of traits — social/human traits —and not just ecological traits. My work developing metrics of traits related to human nutrition is a first step towards developing a more inclusive understanding of traits for socio-ecological systems.

The full article,  Nutritional functional trait diversity of crops in south-eastern Senegal is a part of the Special Feature, Functional traits in agroecology and available in Journal of Applied Ecology.

Read more blogs from the series:

• Leveraging functional diversity in farm fields for sustainability by Jennifer Blesh
• Finding evidence for land restoration strategies by Madelon Lohbeck
• Functional traits represent a key nexus between scientific and local knowledge by Marney Isaac
• Functional traits in agroecology: advancing description and prediction in agroecosystems by Adam Martin