Both organic farming and flower strips support biodiversity, but organic farming is more profitable at field scale

Abstract

Agri-environment schemes (AES) have been introduced to counteract the negative environmental effects caused by increased agricultural intensification in Europe (1). AES approaches can be also classified according to whether they prescribe management in non-productive areas, such as field boundaries and wildflower strips, or in productive areas, such as arable crops or grasslands. Here we test the ecological and economic effectiveness of the two most popular AESs in Lower Saxony, Germany: wildflower strips next to winter wheat fields as off-field practice and organic farming on winter wheat fields as on-field practice. For doing this we selected ten landscapes along a field size gradient with three wheat fields, one conventional field with flower strip, one organic field and one conventional field without flower strip as a common control (the two conventional fields were owned by the same farmer per landscape). During two consecutive years we surveyed plants in field margins, field edges and field interiors; we sampled carabids, spiders and rove beetle by pitfall traps in field edges and field interiors; we sampled bees and hoverflies by transect walks and sweepnetting in field margins. Additionally, we performed detailed economic interviews with our organic and conventional farmers to get revenue, cost and profit data per study field. Plants benefitted far the most from organic farming, whereas flowering strips had only a positive effect on plant richness in field margins, but no effect in the fields compared to the control. As expected due to the high flower cover, flower strips supported three times more bee species and only about 25% more hoverfly species than organic farming, with both AESs being more effective than the control. Finally, both AESs supported equally well carabids and spiders with about 20-30% higher species numbers than the control with exception of rove beetles, which rather avoided fields with flower strips in contrast to control and organic fields. Field size showed only a slight negative trend on the biodiversity of study taxa probably owning to the relatively short gradient in the small-scale agroecosystem of the study area (see also 2). Economic analyses showed the highest costs in control conventional fields and the highest revenues in organic fields leading to more than two times higher profit in the latter one, whereas fields with flower strips compromised a bit lower profit than the control. Wheat yield was about 90% higher in both types of conventional fields than in organic fields. In summary, both AES support farmland biodiversity depending on the taxonomic group at the field scale. The next question is how the effectiveness changes, when scaling up to farm scale or higher scale, or correcting for yield loss between the two AES. References (1) Batáry et al. 2015. Conserv. Biol. 29: 1006‒1016. (2) Batáry et al. 2017. Nature Ecol. Evol. 1: 1279‒1284.