Devastated forests: Severe outbreaks can cause large scale forest mortality. The outbreak that occurred in Northern Fennoscandia during the 2000’s affected more than 10.000 square km of forest in one or more years. Some places in eastern Finnmark more than 80% of the birch trees were killed in the course of a few years.
Hungry caterpillars: Outbreaks by leaf-eating moth larvae is the most important natural disturbance factor in the mountain birch forest. During large outbreaks the larvae can eat up almost every leaf in the forest and change the living conditions for many other animal species.
Three species: Currently three moth species contrubute to these outbreaks and we do research on all of them. It is the autumnal moth (Epirrita autumnata, upper picture on the left), the winter moth (Operophtera brumata, middle picture) and the scarce umber moth (Agriopis aurantiaria, lower picture). All three species belong to the Geometridae and have very similar life cycles.
From eggs to adults: Adult moths mate in the autumn, and the females lay their eggs on the branches of the birch trees. The eggs overwinter and hatch the following spring at the same time as budburst in the mountain birch. The larvae feed on the new birch leaves for 4-8 weeks. During this time they grow through 5 stages (instars). When they reach the 5th instar they drop to the ground and pupate. In autumn they emerge again as adult moth.
Did you know?
- That the females of both the winter moth and the scarce umber moth cannot fly as they have reduced wings. When they emerge from their pupae in autumn, they have to walk all the way up to the tree tops to mate and lay their eggs [see video clip]
- That the eggs of the moths are extremely cold tolerant. In mid-winter they can tolerate temperatures down to -32°C – -37°C. The autumnal moth is the most cold tolerant of them all.
- That it is very important for the moth larvae to hatch at the same time as bud burst of the trees. If they hatch to early they have nothing to eat and will quickly starve. If they hatch too late the birch leaves may be too tough for the tiny larvae to feed on. Timing is everything for the moth larvae!
The mountain birch forest
At the brink of the Arctic: Northern Fennoscandia consists of the northern parts of Norway, Finland and Sweden. In this region, the mountain birch forest (light green on the map below) forms the ecotone between the boreal coniferous forest (dark green areas on the map) and the alpine and low-arctic tundra areas (grey areas on the map). These sub-arctic mountain birch forests, characterised by a climate that that has both oceanic and continental elements, are almost exclusively a Fennoscandian phenomenon, with a midpoint in northern Norway.