The importance of spatial and temporal scale for agri-environment scheme delivery




There is currently little evidence that wider countryside agri-environment scheme (AES) management has led to population-level benefits for farmland birds and it is timely to consider why this might be the case, so that AES options can be improved if necessary. Two reasons why particular options might not deliver landscape-scale population benefits are that they do not take account of the full temporal scale of a resource gap for birds and that they do not provide resources at an appropriate spatial scale for the target population. This paper reviews the published evidence on both issues, focusing on the results of landscape-scale field experiments that used winter seed provision as a model AES option. There is strong evidence that most existing measures that aim to provide overwinter food resources for granivorous birds fail to do so during the late winter period, when the need for the resource is likely to be greatest. Consideration of within-season changes, such as vegetation growth and management of vegetation height, could also increase the value of options such as field margins for birds. Published research and new data together suggest that a separation of c. 1 km between winter food patches would provide all individuals in local Chaffinch Fringilla coelebs and Yellowhammer Emberiza citrinella populations with access to the resource. This separation tallies well with the recommendation in Environmental Stewardship in England that seed crop patches should be sown in patches no larger than 2 ha, with no more than 3 ha/km2. Spatial scale issues could also be critical for AES success in terms of the degree to which complementary resources, within or between seasons, are sufficiently close to one another for the same birds to access the resources that they need. Although they are based on sound evidence, modern AESs might still be improved by revision of their organization or management prescriptions. Revisions that take both the temporal and the spatial scale of resource provision into account will be necessary if farmland bird population recovery goals are to be met. Such revisions could include seed crops or mixes managed specifically to provide food in late winter and the coordination of AES agreements between neighbouring farms to ensure that sufficient resources are provided at the appropriate spatial scale.