Do wood ants play an important role in carbon and nutrient dynamics in boreal managed forests? (ANTS)

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	Photo:Timo Domisch Ant mound in old-growth forest

Background

Red wood ants (Formica rufa group) are common in boreal and subarctic forests of Fennoscandia, as well as in many coniferous and mixed forests of Central Europe and Asia. These ants have been the focus of extensive research, concerning their social structure, geographical distribution and density, population dynamics and behaviour, forest health and biodiversity. However, our knowledge of the role of wood ants on the carbon and nutrient cycle in boreal forests, of the impact of forest management and stand structure on wood ant distribution and dynamics, as well as of the impact of the ant-aphid-relationship on the growth of boreal conifers is still limited.

Photo:Timo Domisch     Ant mound surface

Wood ants build large above-ground mounds composed of litter (such as needles and twigs) and resin, collected from the surrounding forest stand. During the summer, the ants maintain relatively stable temperature and moisture conditions in their mounds. The organic matter and nutrient concentrations in ant mounds are higher compared to the surrounding forest mineral soil, and temperature is higher and moisture content lower compared to the surrounding forest floor. Ant mounds are sites for carbon and nutrient accumulation, increasing spatial heterogeneity. Mounds may be thus "hot spots", sites of high CO2 emission, resulting from decomposition or organic mound material, ant respiration and respiration of tree roots growing into the mound.

Photo:Anita Risch
Photo: Lotta Sundström Ants and aphids

Red wood ants live in a mutual relationship with aphids living on trees, protecting them against their enemies, and tending them for honeydew. Thus there exists an energy flow from the trees into the ant mounds. The growth of trees probably increases where ants prevent other herbivores attacking the trees. The conifers of Fennoscandia, however, have very few defoliating herbivores, and may thus not benefit from the ant predation on leaf defoliators, while the ant-aphid-relationship can reduce their growth.

	Photo:Timo Domisch Ant mound on clear-cut area

Large-scale disturbance, such as timber harvesting by clear-cutting, can make wood ants abandon their mounds, and the area may be colonised by other ant species, nesting under woody residues or in mineral soil, and living without ant-aphid-mutualism. After abandonment, temperature and moisture content in the mounds would change dramatically, altering organic matter decomposition and nutrient mineralisation, and leading to mounds being "hot spots" for CO2 emission. On the other hand, CO2 emission from the mounds may decrease due to the decreased ant population.