Changes in treeline community after an outbreak of a new geometrid species

Lead Author Otso, Suominen
Institution Contact Kevo Subarctic Research Institute University of Turku FI-20014 Turku Finland
Co-Authors Piippa Wäli, University of Oulu, Finland, Anna Liisa Ruotsalainen, University of Oulu, Finland Karita Saravesi, University of Oulu, Finland Maarit Kaukonen, Metsähallitus, Finland Karoliina Huusko, University of Oulu, Finland Heini Koivuniemi, University of Oulu, Finland Annamari Markkola, University of Oulu, Finland
Theme Theme 1: Vulnerability of Arctic Environments
Session Name 1.7 Invasive species in Arctic ecosystems in the changing world: Is it a real threat?
Datetime Wed, Sep 14, 2016 11:05 AM - 11:20 AM
Presentation Type Oral
Abstract text Winter moth (Operophtera brumata) has expanded its range into northern continental areas in Fennoscandia. The first known outbreak of this species in Finnish Lapland occurred in 2005-2009. It led to defoliation of 400 km2 of mountain birch forests at the northern treeline in Finland. We have followed several biotic variables after the outbreak. The amount of alive birches and the coverage of dwarf shrubs declined dramatically during the outbreak. Especially, crowberry (Empetrum nigrum) suffered badly. If the outbreak lasted only one year, approximately half of the birches died and Empetrum dominated field vegetation recovered mostly during the first five years after the outbreak. If the outbreak continued for two or more consecutive summers, the death of birches was often total, grasses took over the field vegetation and the recovery of the dwarf shrubs was very slow. By 2015 it seems evident that parts of the damaged areas will turn from forest to treeless tundra. The berry production of Empetrum and Vaccinium shrubs ceased after the moth outbreak. In forests defoliated once berry production had recovered in 2012. In forests defoliated during several summers berry production of shrubs recovered only in 2014. Fruitbodies of ectomycorrhizal fungi of birch were virtually absent on damaged plots whereas saprophytic macrofungi increased their fruiting along the moth damage gradient. Arbuscular mycorrhiza and shoot endophytes of the grass Deschampsia flexuosa lightly benefited of the moth damage whereas the impact on root endophytic community was negative. Population densities of three vole species and the total rodent abundance increased with the increased moth damage after the outbreak. Only one vole species favored the undamaged forests. These differences were noticeable even in 2015. Snow track counts revealed that winter densities of willow ptarmigan and mountain hare crashed in the damaged forests after the outbreak.
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