Published source details
Clough Y., Holzschuh A., Gabriel D., Purtauf T., Kleijn D., Kruess A., Steffan-Dewenter I. & Tscharntke T. (2007) Alpha and beta diversity of arthropods and plants in organically and conventionally managed wheat fields. Journal of Applied Ecology, 44, 804-812
German organic famers receive subsidies through European agri-environment schemes. This study compares plant, insect and spider communities in organic and conventional wheat Triticum aestivum fields in Germany, considering differences in diversity at both field and regional scales.
Forty-two paired organic and conventionally-farmed wheat fields were surveyed from 21 sites, seven in each of three regions of Germany: the Soester Boerde (51°35’N; 008°07’E), the Leine Bergland (51°32’N;009°56’E) and the Lahn-Dill Bergland (50°49’N; 008°46’E). Fields were 1 – 12.5 ha in size, and pairs had similar size and soil conditions. Organic farmers use no synthetic fertilizers, or pesticides, and rely on organic manures, clover Trifolium leys and crop rotations to suppress weeds and retain soil fertility. Fifteen of the 21 fields in this study were comb-harrowed, sometimes more than once in the season, a practice that may be detrimental to some ground-dwelling arthropods such as spiders.
Vascular plants, bees (Hymenoptera, Apoidea), spiders (Araneae), ground beetles (Carabidae) and rove beetles (Staphylinidae) in each field were sampled along two 95 m x 1 m transects, one along the field edge, one in the centre, between May and July 2003, using quadrats (plants), sweep-netting (bees) and pitfall traps (spiders/beetles).
The number of plant and bee species in a given field was significantly higher in organic fields than conventional fields, but this was not the case for spiders, ground beetles or rove beetles.
For bees and plants, diversity between sites as well as within sites was greater for organic fields than for conventional fields. This means bee diversity improved under organic wheat farming at the larger landscape, as well as the local level.
For spiders, diversity between sites was lower for organic fields than conventional fields. Across the entire study, there were more spider species in conventional fields than organic fields.
The authors conclude that whilst organic agriculture benefits some groups, other species groups such as spiders and beetles need more targeted measures.