Providing evidence to improve practice

Individual study: Organic farming increases the diversity and abundance of wild bees on annually mown fallow strips in Soester Boerde, Leine Bergland and Lahn-Dill-Bergland, Germany

Published source details

Holzschuh A., Steffan-Dewenter I. & Tscharntke T. (2008) Agricultural landscapes with organic crops support higher pollinator diversity. Oikos, 354-361

Background

German organic farmers receive subsidies through European agri-environment schemes. This study compares bee communities on permanent fallow strips next to organic and conventional wheat Triticum aestivum fields in Soester Boerde, Leine Bergland and Lahn-Dill-Bergland, Germany.

Action

Permanent fallow strips next to 21 organic and 21 conventionally-farmed wheat fields were surveyed. Strips were 2.6 m wide on average with grass and herb vegetation. They were annually mown and most included a ditch.

Organic fields were paired with conventional fields of similar size and soil conditions. There were seven pairs in each of three regions: Soester Boerde, Leine Bergland and Lahn-Dill Bergland. Organic farmers use no synthetic fertilizers or pesticides.
All bees were surveyed for 15 minutes along a 100 m transect the width of each fallow strip, four times between May and July 2003. Paired sites were surveyed consecutively, between 10:00 h and 18:00 h, with low wind speed, temperature at least 18° C and less than 30% cloud cover.
All plant species in flower were recorded and the percentage flower cover estimated on the fallow strip transects, and two other 100 x 1 m transects, in the centre and 1 m from the edge of each crop.

Consequences

Fallow strips next to organic fields had more bee species and more individual bees than strips next to conventional fields (average totals over four surveys: 6.33 species, 8.5 bumblebees and 2.6 solitary bees/100 m next to organic fields; 3.95 species, 3.7 bumblebees and 1.1 solitary bees/100 m next to conventional fields).

 

In total, 1,612 bees from 40 species were recorded, including 17 species of Andrena, seven species of bumblebee Bombus and four species of Nomada (parasitic solitary bee).
Flower cover and plant species richness were significantly higher in and near organic than conventional fields. Average flower cover was 2.9% and 3.3% in organic fields and fallow strips respectively, compared to 0.09% and 1.2% in conventional fields and strips. There were 12.6 and 16.9 flowering species on average in organic fields and fallow strips respectively, compared to 5.4 and 12.5 flowering species in conventional fields and strips.
Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://www3.interscience.wiley.com/journal/118531693/home