The increasing evidence for effects of biodiversity on ecosystem properties and processes indicates that effects may vary strongly over the range of studied systems. In order to explore patterns and draw some preliminary conclusions on biodiversity effects in different ecological contexts, we have compiled empirical data from original studies and reviews on effects of biodiversity in natural, agricultural, and forestry systems. We classified hypotheses according to observed ecosystem variables and trophic contexts; trophic contexts were distinguished according to the trophic position of the observed ecosystem variable and the trophic position of the organismic group whose diversity is hypothesized to cause an effect. With four basic ecosystem variables and 14 trophic contexts we obtained 56 permutations or specific hypotheses. Of these, 20 have so far been experimentally tested. We review the results reported from experimental tests of each hypothesis and examine how the reported effects are associated with characteristics of the studied systems.In natural communities, positive effects were most consistently observed for plant diversity affecting plant productivity and stability thereof and, in a broad sense, nutrient retention. Positive diversity effects were most prominent in grassland-type ecosystems, in experimental diversity gradients, with intermediate-to-high species numbers and wide ranges of the diversity gradient, or with randomized species composition. While some of the studies found negligible effects of biodiversity, effects that are beneficial to humans were found in a wide range of ecosystem contexts, even at the limited time scale of ecological experiments. However, our analyses indicate that general statements or predictions about effects of species diversity can only be made with reference to specific variables and trophic contexts. Our classification of hypotheses should help to identify unexamined research questions and to group the variety of hypotheses into classes in which potential diversity effects are mediated by similar mechanisms, thus yielding a more consistent explanatory pattern of experimental results.

One of the main problems in using environmental cost -benefit analysis is deciding on the relevant population: whose benefits should we count? This is important since aggregate benefits depend on both per-person benefit and the number of beneficiaries. Yet this latter term is often hard to evaluate. Distance-decay functions are one way of addressing this problem. In this paper, we present estimates of distancedecay functions for a particular environmental improvement, namely a reduction in low flow problems on the River Mimram in Southern England. We do this both for users and non-users, in the context of a contingent valuation study of the benefits of improving low flow conditions. We test whether distance-decay effects for mean Willingness to Pay are stronger for a single environmental good (the River Mimram, in this case) than for a more inclusive set (here, all rivers in Thames region which suffer from low flow problems). Finally, we explore the impact on part -whole bias, in terms of the relationship between WTP for an individual site and WTP for a more inclusive group of sites, of allowing for distance-decay effects. q

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With rapid urban expansion and loss of open space, attractive local landscapes will continue to gain importance in location decisions and on political agendas. The present study reviews the evidence on the local economic role of landscape amenities from two major strands of empirical research, migration and regional economic models, and hedonic pricing models. Following common amenity definitions we identify 71 relevant peer-reviewed studies and systematically assess the reported effects of the landscape amenity variables. The migration and regional economic studies suggest that migrants are attracted by amenities nearly as often as by low taxes. Reported effects of amenities on income and employment are less consistent. The hedonic studies suggest that nature reserves and land cover diversity have mostly, open space and forest often, and agricultural land rarely positive effects on housing prices. Studies at larger geographic scales and studies involving urban areas were more likely to identify significant amenity effects. Some limitations of the evidence may be overcome with better datasets and modeling approaches. However, in line with other recent work, the limitations also highlight the need for complementary information from the analysis of political preferences for land-use management. to gain importance in location decisions and on political agendas. The present study reviews the evidence on the local economic role of landscape amenities from two major strands of empirical research, migration and regional economic models, and hedonic pricing models.Following common amenity definitions we identify 71 relevant peer-reviewed studies and systematically assess the reported effects of the landscape amenity variables. The migration and regional economic studies suggest that migrants are attracted by amenities nearly as often as by low taxes. Reported effects of amenities on income and employment are less consistent. The hedonic studies suggest that nature reserves and land-cover diversity have mostly, open space and forest often, and agricultural land rarely positive effects on housing prices. Studies at larger geographic scales and studies containing urban or suburban areas were more likely to identify significant amenity effects. Some limitations of the evidence may be overcome with better datasets and modeling approaches. However, in line with other recent work, the limitations also highlight the need for complementary information from the analysis of political preferences for land use management.

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Summary 1.Understanding ecosystem responses to plant species loss is essential for the optimal management of grasslands. Recent studies have examined the effects of simulated random species loss in experimental plant communities but not those of realistic non-random species loss resulting from transient extinction pressures in semi-natural grasslands. 2. To investigate the potential effects of non-random species loss on grassland productivity, we established mesocosms with mixed communities comprising 15 plant species, and exposed them to 2 years of high-intensity management (an extinction phase) followed by 2 years of low-intensity management (a restoration phase) allowing recolonization from differentially managed neighbouring plots. In addition, monocultures of each component species were subject to the same extinction-restoration phases. 3. During the extinction phase, species with high monoculture biomass had lower extinction probabilities in the mixed community than species with low monoculture biomass, but there was also species-specific variation. The species that were most productive or most persistent during the extinction phase were not the same as those performing best in the restoration phase. 4. No consistent effects of spontaneous recolonization from neighbouring communities on species richness or productivity of the focal communities were observed during the restoration phase. 5. We estimated that extinction of all but the species with the lowest extinction risk reduced biomass productivity by 42-49%; loss of all but the four species with the lowest extinction risk reduced it by 2-35%. Identical calculations for a random extinction scenario yielded reductions of 52% and 26-54%, respectively. 6. Synthesis and applications . Prediction of the effects of species loss on plant production and on other aspects of ecosystem functioning in semi-natural grasslands must account for both specific non-random extinction processes and post-extinction conditions. For European mesic grasslands experiencing a shift from high-intensity to low-intensity management, our results suggest that recolonization by 'missing' species must be actively assisted if high production is a management objective.

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