Abstract
The goals of the research theme were: 1. To integrate ecological research on large-scale processes and population dynamics into the development of organic farming systems, and use this 2. To develop methods for efficient biological control and biodiversity conservation in organic production. The program appointed 3 Ph D students in 2002-03, another one in 2005, and has shared a Ph D student with the thematic research program The ecology of the cultivation system - Green manure as a multifunctional in vegetable production (B. Rämert). The Ph D students worked in the following areas: (1) Conservation biological control (Sandra Öberg, Maria Björkman) (2) Landscape ecology and biodiversity (Maj Rundlöf, Johan Ahnström) (4) Farmer participation and ecosystem services (Johan Ahnström) A fifth Ph D project also started on Evolution in the agricultural landscape. This student quit after two years to take over the family farm. The work done was written up during 2007-08 and is now in press (see below). Results Biological control Based on previous results, we hypothesised that spiders would be more abundant and more diverse on organic farms and in heterogeneous landscapes, and hence be important for biological control. We investigated if and when spiders recolonise cereal fields in spring, when they have the potential to suppress establishing pest aphid populations. Linyphiid spiders recolonised fields after being negatively affected by sowing in spring. Lycosid spiders recolonised winter cereal fields after overwintering, and were unaffected by sowing. Linyphiid migration was positively influenced by landscape heterogeneity in the beginning of spring. Diversity of lycosid and linyphiid spiders was positively influenced by perennial crops and forest in the surrounding landscape. Field margins were a key habitat for the diversity of both spider families. Lycosid abundance was affected on the habitat scale and linyphiid abundance on the larger landscape scale, which can be explained by the families' different modes of dispersal. Conventional and organic farms contained different compositions of lycosid and linyphiid species. Body condition of a species of the genus Pardosa (Lycosidae) was higher in landscapes dominated by large fields with annual crops, irrespective of farming system. Hence, spiders were present in crop fields early in spring when they have the opportunity to suppress establishing aphid pests. Different spider species were associated with different farming systems, but the abundances of the most common species were enhanced by organic management. A diverse landscape with easy access to perennial crops and field margins will augment both number of species and individuals of spiders In another Ph D project, the turnip root fly (Delia floralis), a pest insect on Brassica crops in the northern temperate regions of the world, was examined. Intercropping reduced D. floralis oviposition compared with monoculture. The effect of intercropping may be enhanced if D. floralis is provided with alternative oviposition sites. Natural enemies reduced the final pupal numbers of D. floralis, showing that it is possible to retain the predation pressure in intercropped systems despite lower predator activity-densities and D. floralis egg numbers. In a greenhouse experiment, D. floralis pupal weight decreased in response to both intercropping and larval density. This impaired larval development resulted from changes in host plant quality, which included decreased biomass, lower root nitrogen levels, higher root fibre content and altered glucosinolate concentrations. Information on plant responses to herbivory can identify quality aspects that may improve pest insect regulation in these systems. It was found that the weed Circium arvense had a different genetic composition on organic farms compared to conventional farms and natural habitats in central Sweden. This indicates that different farming systems may result in different selective pressures. Biodiversity The work on biodiversity and farming systems consisted of three parts. Firstly, we reviewed and summarised the literature on effects of organic farming on diversity in a meta-analysis. We showed that while there was usually a positive effect of organic farming on diversity, the effect varied between organism groups and studies. Most importantly, the analysis suggested that both study scale and landscape composition influenced the effect of organic farming. The paper also identified the farmers as important actors influencing diversity. In the second part, we used an elaborate pseudo-experimental design to examine the hypothesised landscape effect on the effects of organic farming on diversity of bumblebees and day-flying butterflies. We found that organic farming caused the largest increase in homogenous intensively farmed landscapes, while the effect in heterogeneous landscapes was less pronounced, in line with the hypothesis. In addition, the abundances of bumblebees with small and large colonies were positively associated with organic farming, while species with medium sized colonies instead were affected by landscape heterogeneity, indicating differences between groups in sensitivity to fragmentation of resources. Finally, for butterflies there was besides a local positive effect, also a positive effect of the amount of organic farming in the surrounding landscape, which also increased diversity on conventional farms. In the third part, we studied the possible relationships between farmers? views of nature and the biodiversity on their farms. Decisions concerning farming systems and farm management are taken by the farmer and since these decisions have consequences for biodiversity the motivations behind them need to be understood. Semi-structured open-ended interviews were conducted with 16 farmers in south-central Sweden, together with inventories of species richness on their fields and farmsteads. Bird species richness on the farmsteads was positively affected by the area of houses and animal production on the farm. Species composition was also associated with composition of the surrounding landscape. Biodiversity, measured as an index including five organism groups, increased significantly with farmers' interest in nature and decreased with local farming intensity, measured as crop density. Summary Firstly, our studies show that farmers and their interest in nature may need to be included when designing and studying future management practices in agricultural landscapes, for sustainable production and maintaining biodiversity and ecosystem services in the long term. Secondly, farming practices and landscape composition affect both biodiversity and the efficacy of biological control agents, implying that farmers can manage their farms to increase biological control, and presumably also other ecosystem services such as pollination. However, there was variation in responses to the farming systems and landscape structure between organisms with different traits, for example the two spider families and different pollinator groups. This suggests that the same management may not provide the same result for different organism groups, in different landscapes, or for different ecosystem services. Finally, our results suggest that the effectiveness of agri-environment schemes to promote biodiversity may depend on the landscape heterogeneity and on how large proportion of a landscape that are subjected to the scheme. These results consequently imply that to increase the efficiency of AES it may be important to consider the spatial arrangement of schemes and their allocation at a landscape scale.
Sweden