Background: Large areas of heathland landscapes in Galicia, north-west Spain, have traditionally been extensively grazed by free-ranging cattle and wild ponies. Recently, a large reduction in the number of these larger herbivores has been observed, with unknown consequences for the habitat.
Aims: To evaluate the effects of grazing and herbivore density on plant diversity, community composition and vegetation structure of the endemic wet heathlands dominated by Erica mackayana in Galicia.
Methods: Field sampling of vascular plants, generalised linear models (GLMs), non-metric multidimensional distance scaling (NMDS).
Results: Grazed sites had significantly higher total and rare species richness and diversity than ungrazed sites. Higher densities of cattle resulted in lower numbers of rare species, while wild pony density had no effect on rare species richness. In grazed sites, vegetation was lower with greater variation in height, resulting in greater heterogeneity of the habitat. Precipitation and summer temperatures were related to plant diversity, mainly beta diversity. Soil organic matter negatively correlated with rare species.
Discussion: Grazing, mostly by wild ponies, was demonstrated to be positively related to plant diversity and vegetation structure. Lack of grazing or high cattle densities resulted in a negative effect on total and rare species richness and diversity. Future climate change may negatively affect heathland plant diversity. Galician wild ponies represent a unique case of sustainable management of a wild species and an invaluable cultural heritage. Moreover, they have a significant role in maintaining the endemic E. mackayana heathlands, what would justify specific conservation actions for these large herbivores. 相似文献
Soil properties are thought to affect annual plant productivity in rangelands, and thus soil variables that are consistently correlated with plant biomass may be general indicators of rangeland health. Here we measured several soil properties (e.g. aggregate stability, organic carbon, total nitrogen) and tested each as a would-be predictor of local variation in peak aboveground grassland biomass. Individual properties explained a slight (≤10%) amount of variation in plant biomass. Plant biomass was mainly (negatively) associated with two soil properties, subsurface soil carbonate concentration and the stability of soil macroaggregates near the soil surface. Less important predictive variables included: elevation, plant community composition, surface soil organic carbon, and soil carbon:nitrogen. Plot-to-plot variation in plant biomass is seemingly difficult to predict based on soil properties, including popular indicators of soil and rangeland health and even root biomass. While protection of soil is critical to overall rangeland ecosystem function, our findings suggest that the relationship between soil properties and plant biomass in natural grasslands is complex. Thus, there may not be one or even several soil properties that consistently predict appreciable variation in peak grassland biomass, especially variation within an ecosystem independent of precipitation. 相似文献
Using data from the National Longitudinal Survey of Adolescent to Adult Health, we estimate the effect of peers’ alcohol consumption and alcohol prices on the drinking habits of high-school-age youth. We use the two-stage residual inclusion method to account for the endogeneity of peer drinking in nonlinear models. For our sample of high school students, we find that peer effects are statistically and economically significant regarding the choice to participate in drinking but are not significant for the frequency of drinking, including binge drinking. Regarding alcohol prices, even though we have good price variation in our sample, alcohol prices are not found to be significant. The results are important for policymakers who are considering policies to reduce underage drinking, as we conclude that no significant impact on underage drinking will result from low-tax states’ increasing excise taxes on alcohol so they are similar to those of high-tax states. Policymakers may choose to focus instead on the influence of peers and changing the social norm behavior. 相似文献
Healthier eating is a global challenge for chronic disease control. Food and Health Research in Europe (FAHRE) surveyed research structures and programmes in 32 countries, and reviewed research needs and gaps across nine themes. Food processing and safety research, nutrition and molecular research, and disease-based clinical research are strong; but research is weak on determinants of disease and healthier eating through policies and changing behaviours. Biomedical and commercial research for patents contrast with social research for the public interest. More funding and capacity support should go to social research in the food and health sector. 相似文献