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Predation on artificial ground nests in birch forests fragmented by spruce plantations

Einarsen, Gøøril, Hausner, Vera H., Yoccoz, Nigel G., Ims, Rolf A.
Écoscience 2008 v.15 no.2 pp. 141-149
Betula pubescens, Corvus corone, Lagopus lagopus, Lyrurus tetrix, Picea abies, Vulpes vulpes, buildings, crows, forests, habitat fragmentation, land use, landscapes, nests, plantations, planting, predation, predators, roads, spatial variation, Norway
Spruce planting (Picea abies) in coastal birch forests (Betula pubescens) of northern Norway could influence ground-nesting species such as willow ptarmigan (Lagopus lagopus) and black grouse (Tetrao tetrix). Predator-specific predation rates on baited trackboards were therefore studied in 3 successional edge gradients: birch forest adjacent to (1) closed spruce plantations, (2) open spruce plantations, and (3) clearings. We also examined the influence of 2 types of landscape-level variables on predation rates: the distance from sampling location to the nearest roads and buildings and the land use composition within a 1-km radius of the sample. Predation rates were dominated by 2 generalist species: red fox (Vulpes vulpes) (19.2%%) and hooded crow (Corvus corone cornix) (7.5%%). Predation appears dependent on the successional stage of spruce plantations, with areas near clearings (63.5%%) and open spruce plantations (59.8%%) experiencing higher predation pressures than closed spruce plantations (45.3%%). However, predation rates were highly variable among landscape blocks. Neither landscape nor vegetation variables could explain this block-level variation. We discuss alternative mechanisms that could explain differences between landscape blocks, but further studies are needed to understand the spatial heterogeneity of predators at larger scales.Nomenclature: Mitchell, 1974; Svensson et al., 1999; Macdonald, 2002.