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Interacting effects of agriculture and landscape on breeding wader populations
- Jóhannesdóttir, Lilja, Gill, Jennifer A., Alves, José A., Brink, Sigmundur H., Arnalds, Ólafur, Méndez, Verónica, Gunnarsson, Tómas Grétar
- Agriculture, ecosystems & environment 2019 v.272 pp. 246-253
- agricultural development, agricultural land, altitude, biodiversity, breeding, coasts, fertilizers, habitats, highlands, homogenization, landscapes, meadows, wetlands, Iceland
- The capacity of different landscapes to sustain viable populations depends on the spatial and temporal availability of key population-specific resources. Heterogeneous landscapes provide a wider range of resources and often sustain higher levels of biodiversity than homogeneous ones. Across the globe, agricultural expansion has resulted in large-scale homogenisation of landscapes with associated declines in many taxa. However, during the early stages of agricultural development, in terms of area and intensity, increased landscape heterogeneity and changes in local productivity through fertilizer inputs can potentially increase resource availability for some species. Agriculture in Iceland is currently neither highly intensive nor extensive, and primarily occurs as hayfields (>90% of agricultural land) embedded within a mosaic of semi-natural wetlands and heaths. These landscapes support internationally important breeding populations of several wader species but the role of agricultural land in promoting or constraining breeding wader densities is currently unknown. Understanding the relationship between cultivation and wader populations is important as the area of cultivated land is predicted to expand in Iceland in near future, largely through conversion of the remaining semi-natural wetlands. Here we (a) quantify relationships between breeding wader densities in lowland Iceland and the amount of cultivated land and wetland in the surrounding landscape using density estimates from 200 transects in common semi-natural habitats, (b) assess the extent to which cultivated land affects wader densities in these landscapes, and the potential effects of future agricultural expansion at the expense of wetlands on wader populations. Wader densities in semi-natural habitats were consistently greater when surrounding landscapes had more wetland at scales ranging from 500 m to 2500 m, indicating the importance of wetland availability. However, the effects of cultivated land in the surrounding landscape varied with altitude (ranging from 0 to 200 m); in low-lying coastal areas, wader numbers decline with increasing amounts of cultivated land (and the lowest densities (<1 km2) occur in areas dominated with cultivated land), the inverse occurs at higher altitudes (>100 m a.s.l., where lowest densities occur in areas without cultivated land). This suggests that additional resources provided by cultivated land may be more important in the less fertile uplands. Further agricultural conversion of wetlands in low-lying areas of Iceland is likely to be detrimental for breeding waders, but such effects may be less apparent at higher altitudes.