Publications
NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.
2005
Abstract
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Authors
Bjørn ØklandAbstract
Ips typographus is considered the most destructive of the bark beetles in the coniferous forests of the Palaearctic region. At low population densities this species breeds in fresh windfalls or dying trees of Norway spruce. At high densities, in contrast, the beetles may show tree-killing outbreaks at regional scales. Spatio-temporal analyses based on pheromone trap data indicated that large windfall events may be a major instigator and synchronizer of beetle outbreaks in areas subjected to regionalized weather systems. The general dominance of lag 1 density dependence of the time series indicated that the beetle populations are constrained by intraspecific competition for breeding substrates. The time series sequence before the large windfelling of 1987 was however declining without significant density dependence. We suggest this to be a transition period, reflecting a drop in carrying capacity due to depletion of susceptible trees during the preceding outbreak period (1970s) and a drop in beetle number to below the density required to kill trees. A variety of organisms exhibit episodes of explosive population growth, triggered by disturbance events. A new general model is constructed to capture the coupling of disturbance events with resource accumulation / depletion. The model is refined and parameterized using the dynamics of the Ips typographus in Scandinavia as a model system. The waiting times between outbreaks of simulated time series were generally longer and more variable than the outbreak lengths, which agree well with the historical records in the last 250 years. Spectral analysis and logspline density plots of waiting times suggest that the transition from aperiodic to periodic population dynamics should be regarded as a continuum.
Authors
Olavi Kurina Alexei Polevoi Frank Götmark Bjørn Økland Niklas Franc Björn Nordén Kjell HedmarkAbstract
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The genus Leptographium was described in 1927 and currently includes 48 species, with L. lundbergii as the type species. In recent years, the taxonomic status of L. lundbergii has not been uniformly agreed upon and it has been the topic of considerable debate. The problem was compounded by the absence of a type specimen, and the species was epitypified at a later stage. Unfortunately, the whereabouts of the epitype is now unknown. In 1983, Wingfield & Marasas described L. truncatum, which is morphologically similar to L. lundbergii. Based on DNA comparisons and similarities in their morphology, this fungus was reduced to synonymy with L. lundbergii. The loss of the type specimen as well as variation in the morphology of strains identified as L. lundbergii prompted us to re-examine the taxonomic status of this species. A number of strains from various geographic areas were studied. These include a strain of L. lundbergii deposited at CBS by Melin in 1929 (CBS 352.29) as well as the ex-type strain of L. truncatum. The strains were compared based on morphology and comparison of multiple gene sequences. Three genes or genic regions, ITS2 and part of the 28S gene, partial â-tubulin and partial elongation factor 1-α were compared. Strains currently identified as L. lundbergii, represented a complex of species. Strains initially described as L. truncatum clustered separately from other L. lundbergii strains, could be distinguished morphologically and should be treated as a distinct taxon. L. lundbergii is provided with a new and expanded description based on a neotype designated for it. A third group was also identified as separate from the main L. lundbergii clade and had a distinct Hyalorhinocladiella-type anamorph, described here as H. pinicola sp.nov.
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Authors
Päivi Rinne Carl Gunnar Fossdal Sissel Torre Heather Danforth Aksel Granhus Gunnhild Søgaard John Einset Harald Kvaalen Øystein Johnsen Chris Van der SchootAbstract
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Authors
Paivi L.H. Rinne Carl Gunnar Fossdal Sissel Torre Heather Danforth Aksel Granhus Gunnhild Søgaard John Einset Harald Kvaalen Øystein Johnsen Christiaan van der SchootAbstract
No abstract has been registered