دانلود رایگان مقاله نقش مدیریت تالاب در حفاظت از پرنده زمین های کشاورزی

Abstract

Biodiversity declines in agricultural landscapes represent a major conservation challenge. In the UK, some agricultural landscapes contain high pond densities, but many farmland ponds have become terrestrialised since the 1960s, with input of organic material resulting in a decrease in the size and depth of ponds that eventually transform into wet woodland habitats. Pond management, including removal of overhanging scrub and sediment, has proven highly effective in enhancing freshwater biodiversity. However, the implications of this management for farmland bird assemblages are unknown. Bird surveys were undertaken at recently managed, open, macrophyte-dominated and at highly terrestrialised, macrophyte-free ponds in the intensively cultivated farmland of North Norfolk, UK. The diversity, abundance and composition of bird assemblages visiting these ponds were compared to determine responses to pond management by tree and mud removal. Avian species richness, abundance and bird-visit frequencies were all higher at open farmland ponds. The observed patterns of bird occurrence were best explained by management-induced reductions in tree shading that resulted in aquatic macrophyte-dominance likely associated with high emergent invertebrate prey abundance. Moreover, we predict that open-canopy ponds offer greater habitat heterogeneity than overgrown ponds, allowing diversified bird use. Overgrown, terrestrialised ponds were preferred by some woodland bird species. Gamma diversity across the entire pondscape exceeded all individual pond alpha diversity measures by an order of magnitude, suggesting distinct variation in the bird assemblages visiting farmland ponds during different successional stages. Pond management that generates a mosaic of pond successional stages, including open-canopy, macrophyte-dominated ponds, could help to address the long-term decline of farmland birds. We strongly advocate increased agro-ecological research in this field, combined with greater emphasis on ponds and pond management options in agri-environment schemes.

4.3. Pond management and farmland bird conservationThis study suggests that pond management can be considered to be a valuable tool for bird conservation in farmland. It also alludes to the importance of maintaining a mosaic of pond successional stages within agricultural landscapes in order to support a wide variety of bird guilds. However, the relative value of each successional stage will depend on the extent to which it contributes to the existing habitat heterogeneity in a given landscape. The continued terrestrialisation of entire agricultural pondscapes risks eliminating the contribution of open ponds to landscape-level avian diversity. Equally, simultaneous, uniform pond management with associated loss of wet woodland habitat and homogenisation of the pondscape could have detrimental effects for woodland guilds, particularly declining wet woodland species such as marsh tit, which was uniquely associated with semi-overgrown ponds in this study. We recommend that a high level of environmental variability should be maintained across agricultural pondscapes, taking resource and habitat requirements of specialist bird groups most at risk from future declines into account (Gregory et al., 2004; Le Viol et al., 2012).