Organic farms get better over the years

On October 19, at the Department of Ecology, SLU, Dennis Jonason will defend his thesis "Temporal effects of organic farming on biodiversity and ecosystem services".

The thesis is about how the time span after conversion from conventional to organic farming affects butterflies and moths, plants, ground beetles and ecosystem services as weed seed predation (when different organisms eat weed seeds and thus helps to keep the amount of weeds down).

Time lag in the reaction on conversion
The farms that participated in the study have been either conventional or converted to organic for from 1 to 25 years ago. To pay attention to time since conversion is important because there may be a lag in the organisms' response to a change in the environment, which is essential to be aware of when evaluating the effect of organic production.

The results differ between different groups of organisms, and it is also differences in effects depending on whether you look at the diversity of species or at the number of individuals. For example, the number of butterflies increased by 20 percent immediately after conversion, while the number of individuals increased gradually, and was after 25 years from conversion 100 percent more compared to year one.

Moths more common on new organic farms
For plants, the results were slightly different depending on which species that was studied. Creeping thistle and chickweed were common on new organic farms while meadow horsetail and Kentucky bluegrass were common on older organic farms. This indicates that plant communities changes with the time span after conversion.

Moths were quite common on new organic farms, and this is thought to be related to the fact that creeping thistle (which is a valuable nectar and pollen source) also was common on these farms. Ground beetles and seed predation seemed unaffected by time span after conversion.

The thesis demonstrates the importance of taking the time span since conversion into account when evaluating the effects of organic farming on biodiversity and ecosystem services.

The thesis has been carried out within SAPES ”Multifunctional Agriculture: Harnessing Biodiversity for Sustaining Agricultural Production and Ecosystem Services”. SAPES is a research environment that combines ecological and socio-economic research and examines the relationships between land use, biodiversity and ecosystem services in agricultural landscapes.