Temporal effects of organic farming on biodiversity and ecosystem services

Agricultural intensification has caused a dramatic decline of global biodiversity and associated ecosystem services. Organic farming has been shown to partially counteract agricultural intensification by applying environmentally friendly and resource efficient farming practices, but opportunities to improve in efficiency still remain. This thesis investigates the contribution of organic farming to biodiversity and ecosystem services with focus on the effect of the time since transition (TST) to organic farming methods. Surveys on butterflies, plants, moths, carabid beetles and an experimental study on weed seed predation were performed on conventional and organic farms situated in landscapes differing in landscape complexity. The organic farms had been under organic management between 1 and 25 years before surveys. This design allowed for analyzes of the effect of organic farming while accounting for the time since transition and landscape composition. The overall effect of organic farming was small. Only butterflies and plants (in one out of two studies) had higher species richness and abundance on organic compared to conventional farms. However, analyses of the time since transition to organic farming revealed novel facts: butterfly abundance increased gradually by 100% over 25 years, whereas butterfly and plant species richness increased rapidly at the transition and then remained fairly constant. The moths that initially did not appear to increase in the organic farming system showed a clear positive response to newly transitioned farms (TST≤6 years), whereas conventional and old organic farms (TST≥15 years) had similar diversity. Two plant species occurred more frequently on new organic farms and two species on old organic farms. Neither carabids nor seed predation showed any temporal responses to organic farming. This thesis shows that explicitly addressing temporal effects of organic farming may result in novel and unexpected findings. Control for temporal effects opens up for better understanding of the complexities between organic farming, biodiversity and ecosystem services over time. Future evaluations need to address this factor for high credibility and usefulness in the development of improved policies for organic farming