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Doctoral dissertation “Ant community structure in successional mosaics of boreal forests"

Press release 2020-06-05 at 8:00

MSc Pekka Punttila will defend his doctoral dissertation entitled “Ant community structure in successional mosaics of boreal forests " at the Faculty of Biological and Environmental Sciences, University of Helsinki, on June 5th 2020 at 12 noon. Dr Therese Löfroth from SLU Umeå will be the opponent and prof. Liselotte Sundström the custos. The audience can follow the dissertation via Zoom.
 

Abstract

Pekka Punttila

In order to be able to safeguard the native forest species and habitats, and to develop ecologically sustainable management regimes for forestry, we need to understand how human impact has changed the natural successional patterns and structural characteristics of forest stands and landscape composition in boreal forests, and how these changes have affected the boreal biota.

In this work, I tested hypotheses concerning ant-community succession in a patchwork of forest stands of different age and size using data gathered with pitfall trapping and nest-mound mapping mainly in southern Finland. Specifically, I aimed to evaluate the effects of old-forest fragmentation and age-class distribution changes caused by forest management, with a special focus on a group of territorial keystone ant species, the wood ants (Formica rufa group), and the strength of their impact on the forest ecosystem. Wood ants are considered keystone species in boreal forests because of the multitude and magnitude of the ecological interactions of these species both with other forest organisms and with their environment.

The wood-ant dominated system of mature forests was found to disintegrate after severe disturbances such as large-scale clearcutting, and the subsequent ant-community succession followed rather deterministic pathways where nest-founding strategies and species interactions, especially competition and slave-making, played important roles.

The occurrence of territorial wood-ant species matched quite closely the predictions developed based on the social strategies exhibited by the species, and the results suggest that changes in forest-disturbance regime, either natural or anthropogenic, may lead to remarkable changes in wood-ant worker population sizes and, consequently, in the strength of their impact on forest ecosystem processes. Wood-ant communities may experience complete species turnover from the dominance of monogynous (single-queened) species to the dominance of polygynous (multiple queened) ones, or vice versa, depending on the prevailing disturbance regime, and the accompanied changes in worker densities were shown to be much larger than could be predicted from mere nest densities. Such changes may have remarkable impacts on forest ecosystem processes.