Effects of spatial scale and vegetation cover on predation of artificial ground nests

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Abstract
Scale-dependent effects of landscape heterogeneity on predation of artificial ground nests were studied. Two spatial scales were selected: landscape grain size and single stand size. The landscape types did not differ from each other in their total predation intensity. Depredation was highest in larger stands in all the landscape types studied and the highest predation rate was detected in the largest stands within the most fragmented landscapes. This is possibly due to concentration of rodent-eating predators from surrounding open areas into large stands in the study year when their main prey, voles, crashed. In crash years, alternative predation on e.g. forest bird nests may play an important role for these predators. The influence of predators concentrating into forest stands is expected to be especially strong in landscapes of fine grain size because such a landscape contains relatively more open areas. The predation rate was independent of the distance of nests from the edges of forestry roads. Direct cover (a branch) placed above dummy nests improved the survival rate of these nests. However, tree canopy cover only had a slight effect on the predation rate. The lacking impact of canopy cover on nest predation may be due to the openness of the northern pine forests which makes it particularly easy for predators to discover dummy nests on the ground.