A cultivated planet: closing yield gaps

By Tibor Hartel and Joern Fischer

The challenge of sustainably increasing global food production was recently addressed by Foley et al. in Nature. Among other solutions, they suggested closing yield gaps in existing agricultural land, rather than converting new areas for agriculture. A yield gap is the difference between the actual agricultural productivity of land and its potential productivity. Foley et al. considered that much farmland in Eastern Europe had high yield gaps (see also Licker et al. 2010).

We broadly agree with Foley et al., but we also think we shouldn’t be too enthusiastic about closing yield gaps. In the case of Eastern Europe, three questions must be addressed: (i) What should be the reference point for closing yield gaps? (ii) Which specific management and land use should be used to close yield gaps? (iii) How will the closure of yield gaps affect the biodiversity and resilience of agro-ecological systems?

Yields obtained by ‘organic farming’ may constitute a reference point for assessing yield gaps, and organic farming may be a desirable new type of land use. However, organic farming as it is practiced in Western Europe may still constitute more intensive land use than the traditional agriculture practiced until today in some of Eastern Europe. Traditional agriculture has been tested over centuries, and has resulted in species-rich, virtually unfragmented rural landscapes (e.g. in Central Romania). While organic farming tends to support greater biodiversity than conventional (industrialised) agriculture, its consequences for biodiversity relative to traditional agriculture are poorly understood.

Closing yield gaps could easily be interpreted as analogous to ‘optimal harvesting’ as it has been applied in forestry. However, an overly narrow focus on efficiency in production can risk an system’s biodiversity and resilience (Holling and Meffe 1996). The costs to resilience of closing yield gaps are currently unknown.

Before policy aims to close yield gaps, society needs to consider the unique circumstances of the systems targeted. Otherwise, there is a risk to erode the resilience and biodiversity of some of the world’s most notable rural landscapes.