Effects of Created Habitats on Farmland Biodiversity

Abstract

The main aim of this thesis was to quantitatively assess the effect of created habitats on a range of characteristic farmland organisms, in order to evaluate the potential of created habitats as a way of ameliorating observed negative population trends. But what is "created habitats"? In the agricultural landscape virtually all habitat is created or managed by humans in some respect: most fields are ploughed and sown with different crops on an annual basis; some grass fields remain unbroken for periods up to five years, but the grass sward is managed through the addition of fertilisers as well as more or less frequent cutting; the permanent pastures are grazed by livestock, the type and density of which farmers decide. Through these activities farmers also alter the non-cropped habitats such as field boundaries, since pesticides and fertilisers applied to the crops drift from the fields. So throughout this thesis, created habitat is defined as habitats that have been created not for the (sole) purpose of producing an income-generating crop yield, but habitats that are intended to benefit wildlife in some way, be it by providing food or shelter. However, created habitats may still be beneficial also for the farmer's income by supporting ecosystem services. For example, pollinators attracted to flower strips may also forage in the adjacent crops and enhance pollination of these, thereby increasing the yield. Grass strips and flower strips can harbour natural enemies that reduce crop damage. Different created habitats can provide food and shelter for a range of game species, the hunting of which can provide an income from both sold shoot days and the meat from bagged game.

Most of the created habitats involved in this study have been created by farmers and landowners who care about these things. They have voluntarily taken some of their land out of production to make space for such habitats, and have covered the costs involved themselves (Papers I, II, IV). Other habitat has been created through an AES incentive, 'Fågelåker' (i.e. wild bird cover; Paper III). Measures for reducing farming intensity affect the agricultural habitat, and I have investigated the effects of such measures on farmland biodiversity (increased amounts of ley Papers I, II; organic farming Paper II).

I have investigated the effects of such created habitats on farmland biodiversity at different spatial scales. The reason being that, in order to benefit the intended organism, the habitat needs to be created in such a way that they can be accessed within the organism's range of movements. I have also investigated effects of created habitats on a range of organisms inhabiting the agricultural landscape. If habitats can be created in a way that benefits more than one species or organism group, they will be more cost-effective.

More specifically, the following main questions are addressed in the individual papers included in this thesis:

Paper I Are sown flower strips attractive foraging habitats for pollinators (bees and hoverflies)? Do sown flower strips have the capacity to increase abundances of pollinators in the wider landscape outside of the flower strips, or do they simply redistribute pollinators in the landscape? Is the effect of flower strips dependent on landscape context? Does the effect of flower strips vary over the season?

Paper II Can created habitats and reduced farming intensity increase the density of brown hares? Do these interventions (habitat creation, organic farming, and increased use of leys) have differential effects in landscapes of varying landscape heterogeneity and crop diversity?

Paper III Does wild bird cover (i.e. seed-rich habitat; WBC) increase the abundance of granivorous passerines in winter? Does WBC redistribute birds and cause them to aggregate around the WBC? Are the effects of WBC on birds consistent throughout the winter?

Paper IV Is habitat creation, as exemplified by the GWCT habitat recommendation, capable of increasing grey partridge abundance, breeding success and overwinter survival in Sweden, more specifically in the absence of intensive predator control? Does the GWCT habitat recommendation have added benefits for other species, such that the grey partridge can function as a bioindicator?