Herbivores in forests

This study centers on the interaction of herbivores and Icelandic birch (Betula pubescens) at study sites in contrasting climate in north and south Iceland.

Birch forms the basis for important animal food webs here. The forest is productive in terms of leaf biomass and seed production. Specialist leaf and seed feeding insects and vertebrates are important herbivores in this system, while others avoid the noxious chemicals in birch seeds and leaves.

Outbreaks of insects on Icelandic birch are reported by biologist in this and past centuries. The redpoll (Carduelis flammea) is the most important seed-feeding bird on Icelandic birch while other birds occasionally include birch seeds in their diet.

Traditional sheep grazing still occurs on some native birch forests while other forests are protected. Sheep often prefer young birch to other vegetation while also browsing on birch and other woody species at times when their preferred nonwoody food plants are scarce. A central question is how sheep grazing affects the growth, reproduction and insect resistance of birch. Comparisons are made between birch plants of different age groups and forest habitat, climate and management regimes. The experiments explore grazing responses of young plants, resprouting plants, and mature plant. Detailed tests are made of the importance of timing and intensity of grazing for the regrowth and resistance of birch. Interacting effects of grazing and ambient factors are examined. Information is sampled on sheep grazing practices on birch forests.

Observations are made on the ecology of birch-feeding moth species, for example, Acleris notana in the north and Epinotia solandriana and Operophthera brumata in the south. Local climatic gradients as well as climate differences between north and south Iceland may exert a strong effect on the distribution and abundance of moth caterpillars. Experiments examine birch responses to different caterpillar loads and timing of caterpillar feeding.
A long-term goal of this research is to obtain important comparisons to birch herbivory studies in northern Scandinavia, where B. pubescens grows in different soils and a more continental climate.

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