Agricultural intensification and the destruction of semi-natural landscapes (field copses, hedges, buffer strips, etc.) is one of the primary causes of current biodiversity loss. While reconverting cultivated lands to semi-natural landscapes is often difficult in many areas, increasing the complexity of the crop mosaic by decreasing field size and/or increasing the diversity of planted crops has recently been suggested as an alternative to encourage biodiversity in farmed landscapes while maintaining agricultural production.
This hypothesis has just been tested through a vast study involving 30 laboratories in 8 countries, and involving 8 regions in Europe and Canada. This study is based on observations taken in 1,305 cultivated plots, in 435 agricultural landscapes of 1 square kilometer, in which average field size, crop diversity, and the proportion of semi-natural landscapes varied independently. The researchers identified more than 167,000 individual members of 2,795 species belonging to 7 taxonomic groups (birds, butterflies, bees, hoverflies, spiders, ground beetles, and plants). They then calculated a synthetic index grouping the information on the seven taxonomic groups in order to estimate the biodiversity of each of the 435 studied landscapes.
Through this, the researchers showed, for the first time at such a large geographic scale, that increasing the complexity of the crop mosaic is equally as beneficial to biodiversity as increasing the amount of semi-natural landscapes. For example, a decrease in the average size of the fields from 5 to 2.8 hectares generates an increase in biodiversity comparable to that observed when the proportion of semi-natural landscapes increases from 0.5 to 11%. This study also showed that small fields have a positive effect on biodiversity, including when there is no semi-natural vegetation between the fields (hedges, grass strips, etc.). Crop diversity has a positive impact on biodiversity because different crop types are often home to different species, but also because different crops provide complementary and needed resources for supporting certain species in agricultural landscapes. Crop diversification is especially beneficial in agricultural landscapes where the proportion of semi-natural landscapes is greater than 11%, which represents half of sampled agricultural landscapes in this study.
These results reveal that agricultural landscapes having smaller fields and more diverse crops are home to a greater biodiversity. Increasing the complexity of crops thus represents a little known but valuable tool for conserving and restoring the biodiversity of agricultural landscapes. Agro-environmental policies encouraging a reduction in average field size of cultivated crops and, under certain conditions, more diverse crops, would allow for maintaining high levels of biodiversity and agricultural production areas.