land management that they want to achieve. We may want to reverse the loss of biodiversity and ecosystem services, but what is the appropriate level? Just how many skylarks and linnets is the 'right' number? As there is no market for these environmental services, it is difficult to establish how much additional environmental effort is required. A second issue concerns the recommendation that efforts should be concentrated in those regions where biodiversity (the environmental good measured in this study) can be produced most effectively. This seems appropriate in the case of some environmental issues, for example, carbon storage. The impact of carbon emissions on climate depends on their aggregate level and not on where they are produced, so it makes sense to protect carbon stocks in soils in those regions where this is least costly. The issue is less clear-cut in the case of other environmental issues, such as biodiversity. Is it sufficient that biodiversity is protected in some specific regions (presumably those more marginal for agricultural production) while in other regions monocultural crops are planted field boundary-to-boundary? Apart from the minimum standards which all farmers must observe to prevent water pollution, further improvement in water quality may be desired in particular catchments because of their importance for drinking water supplies or for other reasons. It may not always be sensible to choose the cheapest locations. However, these questions do not invalidate the message of the study which is summarised by Dr Paul Wilson, one of its authors, as follows: