Quantifying the extent to which farmers can influence biodiversity on their farms

Abstract Despite the introduction of agri-environmental schemes, no general increase of farmland biodiversity in Europe has been observed. Farmers take decisions about the implementation of agri-environmental schemes at the farm scale, and it is thus highly relevant to assess the relationship between farm management and biodiversity at this scale to increase the effectiveness of agri-environmental schemes. The present study quantifies to what extent and with which practices farmers can influence biodiversity on their farm and to what extent conditions outside farmers’ control may mediate biodiversity. We grouped 27 variables into four variable sets: (1) ecological compensation (mainly semi-natural habitats), (2) in-field options (e.g. no growth regulator, insecticide and herbicide treatment), and (3) farm characteristics, which can be influenced by farmers (e.g. land-use types) as well as (4) farm settings, which cannot be influenced by farmers (e.g. altitude). As biodiversity metrics, plant, grasshopper, butterfly and bird richness and abundance of farmland target species were assessed on 133 farms of the Swiss Central Plateau from 2009 to 2011. Variance partitioning and generalised linear mixed models were used to analyse the impact of each variable set on farmland species diversity. Our results provide evidence that farmers can indeed positively influence biodiversity by ecological compensation and in-field options. The variables of the ecological compensation set explained the highest proportion in the variation of plant richness and butterfly abundance. We found a significant positive relationship between in-field options and plant abundance. Our study illustrated that the effects of biodiversity-related farming practices differ between species and biodiversity metrics. Conditions outside farmers’ control explained a high variation in grasshopper and bird diversity. One variable within the set of farm settings, the degree of consolidation, had a significant negative impact on five out of eight biodiversity metrics (plant, butterfly and bird richness; plant and bird abundance). We demonstrate that farmers can substantially enhance biodiversity on their farms and provide knowledge on how such biodiversity improvements can be achieved by farmers. Further, we highlight the value of new biodiversity-related management practices such as in-field options.