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Research article - Peer-reviewed, 2006

Effects of tree stand species composition on insect herbivory of silver birch in boreal forests

Vehvilainen H, Koricheva J, Ruohomaki K, Johansson T, Valkonen S


Pure forest stands are commonly believed to be more susceptible to insect herbivore attacks than mixed stands. However, the existing experimental evidence of tree species diversity effects on herbivores in forest ecosystems is scarce and contradictory. In the present study, we compared insect herbivore abundance and leaf damage on silver birch (Betula pendula) in monocultures and paired mixtures with Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) in three experiments in the boreal forest zone (SW Sweden, SW and central Finland). In the Finnish experiment, total densities of insect defoliators were highest in birch monocultures and decreased with increase in the proportion of Scots pine in a stand. Densities of leaf rollers, gall mites and aphids also tended to be higher in birch monocultures than in mixed stands. At the beginning of the season the proportion of birch leaves damaged by chewing insects in the Finnish experiment was significantly lower in mixed stands containing 25% of birch and 75% of pine as compared to birch monocultures and mixtures with 50% of birch and 50% of pine. However, by the end of the season there were no significant differences in herbivore damage between the treatments. In the Swedish experiment, where herbivory monitoring was conducted at the end or at the middle of summer, neither herbivore abundance nor damage differed between birch monocultures and paired mixtures with Scots pine and Norway spruce. Our results provide only a partial support for the hypothesis that pure forest stands are more susceptible to insect herbivores and demonstrate that the benefits of mixed forests in terms of reduced herbivory are not as straightforward as commonly thought

Published in

Basic and Applied Ecology
2006, Volume: 7, number: 1, pages: 1-11

    UKÄ Subject classification

    Forest Science

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