Productivity may have peaked for many food crops, researchers warn

22-Jan-2015 - Last updated on 22-Jan-2015 at 10:13 GMT

Twenty of the resources experienced a peak-rate year between 1960 and 2010, the researchers found

The days of assuming that natural resources can be interchanged when one comes under pressure may be over, according to new research warning that ‘renewable’ does not always mean ‘unlimited’.

Writing in in the journal Ecology and Society, the international research team examined historical production data on 27 non-renewable and renewable resources essential for human well-being and daily needs (energy and food) including corn, rice, wheat, fish, meat, milk and eggs.

They found that renewable resources have become scarcer, with 21 resources having already experienced a peak-rate year.

“Many separate studies have estimated the year of peak, or maximum, rate of using an individual resource ... However, no study has estimated the year of peak rate for multiple resources and investigated the relationships among them,” said the team, led by first author Professor Ralf Seppelt from the Helmholtz Centre for Environmental Research in Germany.

The researchers found that non-renewable ‘conversion to cropland’, and 18 of 20 renewable resources (many of which are food resources) have peaked in productivity.

Seppelt and colleagues said such findings show the days of assuming natural resources can be swapped or substituted to solve short term shortages may be over.

According to the study, 20 of the resources that experienced a peak-rate year for production saw it occur between 1960 and 2010, something that the team suggest is “a narrow time window in the long human history.”

"People often talk about substitution. If we run out of one resource, we just substitute another. But if multiple resources are running out, we've got a problem," said study co-author Professor Jianguo "Jack" Liu, director of the Center for Systems Integration and Sustainability at Michigan State University.

Sustainable production?

Seppelt and colleaguesused a global datasets to analyse resources, sourced from either the United Nations or World Bank data. From this the team used computer modelling to extract production patterns from the databases.

“Renewables include staple crops, e.g., cassava, maize, rice, soybeans, and wheat, which the Food and Agriculture Organization of the United Nations identified as providing 45% of global caloric intake. Combined with data on the consumption of animal products, the main sources of food are included in our analysis,” said the authors.

The team discovered that not only have 21 resources experienced a peak-year, but also that for 16 of these the peak year lay between 1988 and 2008.

"The key commodities that a person needs for food, and must harvest, are limited,” commented Seppelt.

The team illustrated this using various examples, such as the fact that the maximum global growth rate in crop yields for soybeans was in 2009, while peak production for milk was 2004. For eggs it was 1993 and for fish caught it was 1988.