Forest floor moisture controls predator activity on juvenile seedlings on Pinus sylvestris
1997
Nystrand, O. | Granstrom, A.
Conifer seedlings are succulent and vulnerable to animal depredation in the first few weeks after germination. Several animal taxa are reported to feed on seedlings, and field observations indicate varying rates of losses in boreal vegetation. Almost nothing is known about factors regulating seedling predation levels. Here, we test the hypothesis that the risk of predation is affected by the moisture content of the forest floor. The underlying assumption is that slugs are important seedling predators and that their activity depends on the substrate moisture. In a relatively open coniferous forest in northern Sweden, 1-week-old seedlings of Scots pine (Pinus sylvestris L.) were placed out in plots where moisture conditions were experimentally manipulated. There was a significant effect of forest floor moisture on predation. The average predation level for the five experimental rains was over three times higher in watered than in rain-protected plots (68 versus 22%). In unmanipulated plots, average predation was intermediate (49%) but with large variation, and more seedlings were killed during wet than dry periods. The slug Arion subfuscus (Drap.) was the only important seedling predator, with a population density of approximately 3 m-2. Our results show that slug predation can be a quantitatively important mortality factor, acting mainly when conditions otherwise favor seedling establishment. i.e., when the forest floor is moist.
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