Action: Convert to organic farming
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Evidence on the impact of organic farming on wild bees is equivocal. Three replicated trials in Europe or Canada have shown that the abundance of wild bees is higher under organic arable farming than under conventional farming. One of these showed that bee diversity is higher in organically farmed wheat fields and in mown fallow strips adjacent to them. Three replicated trials in Europe or the USA have found no significant difference in the numbers of bumblebees (two trials), bumblebee species (one trial), or wild bees visiting flowering crops (one trial) between conventional and organic arable farms.
Supporting evidence from individual studies
Belfrage et al. (2005) counted bumblebees Bombus spp. on six organic and six conventional arable farms in Roslagen, southeastern Sweden. They found no significant difference in the numbers of bumblebees between the two farm types.
A comparison of organic and conventional canola (oilseed rape Brasscia sp.) fields in Canada found a significantly greater abundance of wild bees in organic fields (averages 86 bees per organic field sample, 58 bees per conventional field; Morandin & Winston 2005).
A comparison of 21 organic and 21 conventional winter wheat fields in northern Germany found a greater abundance and diversity of wild bees on organic fields than on paired control fields (Kleijn et al. 2006, Holzschuh et al. 2007). Average bee species richness per field was 6.9 for organic fields and 2.1 species for conventional fields. 1,326 individuals of 31 bee species (average abundance 63.1) were recorded in organic fields compared to 181 individuals of 16 species (average abundance 8.6) in conventional fields.
Holzschuh A., Steffan-Dewenter I., Kleijn D. & Tscharntke T. (2007) Diversity of flower-visiting bees in cereal fields: effects of farming system, landscape composition and regional context. Journal of Applied Ecology, 44, 41-49
In the same study, the total number of bee species was higher under organic farming whether you considered the number found at individual sites, the total number found in each region or the total for the entire study (Clough et al. 2007). 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 level, as well as the local level.
Also in the same study, Holzschuh et al. (2008) report higher bee abundance and diversity on permanent fallow strips next to organic winter fields, compared to fallow strips next to conventional wheat fields. On average, 2.6 m wide annually mown fallow strips next to organic fields had 6.3 bee species, 8.5 bumblebee individuals and 2.6 solitary bees/100 m in total over four surveys, compared to 4.0 species, 3.7 bumblebees and 1.1 solitary bees/100 m on strips next to conventional fields.
A study of 15 organic and 40 conventional arable field boundaries in Finland found no significant difference in the numbers of bumblebees or bumblebee species (Ekroos et al. 2008). On average, three bumblebees from 1.1 species were recorded per transect on conventional farm field boundaries, and 3.8 bumblebees from 1.4 species on organic farm field boundaries.
Rundlöf et al. (2008) surveyed bumblebees Bombus spp. on 12 pairs of organic and conventional farms in Sweden, and found significantly more bumblebees and bumblebee species on organic than conventional farms (on average 7.7 and 4.9 species/farm on organic and conventional farms respectively). This difference between organic and conventional farms was not statistically significant when only the six pairs of farms in heterogenous (mixed) farming landscapes, with smaller field sizes and more grassland, were considered. So organic farming had a greater effect on wild bumblebees in intensive, homogenous arable landscapes.
Winfree et al. (2008) surveyed wild solitary and social bees visiting flowering crops on 22 or 23 farms, of which six or seven were organic and 16 conventional, in Pennsylvania and New Jersey, USA. Organic and conventional farms did not differ in field size, crop diversity or wild/weedy plant diversity and all lay in a heterogeneous landscape with many small patches of natural habitat such as woodland. They found no difference in either the abundance or species richness of bees between organic and conventional farms.
- Belfrage K., Björklund J. & Salomonsson L. (2005) The effects of farm size and organic farming on diversity of birds, pollinators and plants in a Swedish landscape. Ambio, 34, 582-588
- Morandin L.A. & Winston M.L. (2005) Wild bee abundance and seed production in conventional, organic, and genetically modified canola. Ecological Applications, 15, 871-881
- Kleijn D., Baquero R.A., Clough Y., Diaz M., De Esteban J., Fernandez F., Gabriel D., Herzog F., Holzschuh A., Johl R., Knop E., Kruess A., Marshall E.J.P., Steffan-Dewenter I., Tscharntke T., Verhulst J., West T.M. & Yela J.L. (2006) Mixed biodiversity benefits of agri-environment schemes in five European countries. Ecology Letters, 9, 243-254
- 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
- Holzschuh A., Steffan-Dewenter I. & Tscharntke T. (2008) Agricultural landscapes with organic crops support higher pollinator diversity. Oikos, 354-361
- Ekroos J., Piha M. & Tiainen J. (2008) Role of organic and conventional field boundaries on boreal bumblebees and butterflies. Agriculture, Ecosystems and Environment, 124, 155-159
- Rundlöf M., Nilsson H. & Smith H.G. (2008) Interacting effects of farming practice and landscape context on bumble bees. Biological Conservation, 141, 417-426
- Winfree R., Williams N., Gaines H., Ascher J.S. & Kremen C. (2008) Wild bee pollinators provide majority of crop visitation across land-use gradients in New Jersey and Pennsylvania, USA. Journal of Applied Ecology, 45, 793-802