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Our research activities

Local to meso-scale process-oriented studies

In the field:

Our field studies (commenced in 2001) are primarily conducted in a system of altitudinal gradients and a separate system of island-main transect pairs. Altitudinal gradients are valuable as a a proxy for natural climatic variation in studies of life history responses in insects. The island-mainland transects pairs are specifically designed to elucidate the importance of dispersal versus climate for moth population fluctuations. We focus on the following:

  • Host-parasitoid dynamics in altitudinal gradients
  • Phenological development and timing in moth, birch and parasitoids
  • The role of climate and dispersal on local spatial dynamics
  • Local spatial synchrony and travelling waves
  • The ecology and dynamics of an invasive moth species, A. aurantiaria

In the laboratory:

The timing of larval emergence from the eggs in relation to the timing of budburst in the host tree is a critical stage in the life cycle of birch forest moth and hence for the development of population outbreaks. The process is temperature dependent. In addition to tailored field studies of larval and birch phenology, we study temperature dependent hatching of moth larvae relative to birch bud burst under controlled temperature regimes in the laboratory. We focus on the following:

  • Developing species specific models for the temperature-dependent development (in particular timing of egg hatch) of each moth species

  • The relationship between birch and moth phenology (match/mismatch) under different temperature scenarios (in particular earlier spring)

Large-scale spatial dynamics and pattern analyses

Moth population data are tediously sampled in the field. Ground measures cannot be obtained for large geographical regions. Fortunately, several aspects of the birch forest-moth system makes it suitable for remote sensing approaches: i) severe outbreaks result in (near-)complete defoliation, possibly forest death, which can be observed both from airplane and from satellite, ii) the phenogical stage in birch development that is most important for larval development is the timing of bud burst. This can be determined from satellite. In 2006, we initiated remote sensing studies in order to obtain large-scale information on the distribution, extent and temporal dynamics of severe moth outbreaks. From 2008 this was extended by parallell ground and satellite studies of birch forest phenology. In addition we analyse regional patterns of spatio-temporal outbreak dynamics using historical outbreak records. We focus on the following:

  • Use of remote sensing vegetation indices to identify moth outbreak areas.
  • Surveillance of birch forest phenology (in particular timing of bud burst): from field measures to satellite imagery
  • The relationship between large-scale variation in phenological dates and the distribution of moth outbreaks
  • Spatial dynamics and pattern analyses of historical outbreak records.

Ecosystem effects and management actions

During the last decade as much as 1/3 of the birch forest belt in northern Fennoscandia has been affected by severe defoliation in one or more years. In areas that has suffered prolonged outbreaks, large tracts of birch forest have died and the impacts on the dwarf shrub and herb layers are dramatic. Still, relatively little is known as to the consequences of such large-scale compound disturbances for the mountain birch ecosystem. In collaboration with colleagues from Norut – Northern Research Institute, we study the vegetation composition in plots before and after severe defoliation (Karlsen et al. submitted manuscript 2012). Further, in 2010, we initiated a large-scale survey of the effects of moth defoliation on the moluntain birch forest system in the Varanger region in Finnmark (Jepsen et al. submitted manuscript 2012). To evaluate how forest management may be used to increase forest regeneration following moth outbreaks, we initiated a large-scale clear-cutting experiment in 2011 in collaboration with local forest management and landowners (Finnmark County and the Finnmark property). These initiatives will be contibued in the years to come under the Nordic Centre of Excellence (NCoE) "How to preserve the tundra in a warming climate". We focus on:

  • Forest, shrub and herb layer damage and regeneration following defoliation
  • The importance of initial forest type for succession patterns following defoliation
  • Interactions between moth outbreaks and grazing by large and medium-sized herbivores, and their importance for forest recovery
  • Forestry management actions as tools to increase forest regeneration following moth outbreaks