Publikasjoner
NIBIOs ansatte publiserer flere hundre vitenskapelige artikler og forskningsrapporter hvert år. Her finner du referanser og lenker til publikasjoner og andre forsknings- og formidlingsaktiviteter. Samlingen oppdateres løpende med både nytt og historisk materiale. For mer informasjon om NIBIOs publikasjoner, besøk NIBIOs bibliotek.
2006
Sammendrag
Detailed analyses of thresholded ecological interactions can improve our understanding of the transition from aperiodic to periodic dynamics. We develop a threshold model of the population dynamics of outbreaking bark beetle populations that alternate between non-epidemic and epidemic behavior. The model involves accumulation of resources during low-density periods and depletion during outbreaks. The transition between the two regimes is caused by disturbance events in the form of major tree felling by wind. The model is analyzed with particular reference to the population dynamics of the spruce bark beetle (Ips typographus) in Scandinavia for which a comprehensive literature allows full parameterization. The fairly constant outbreak lengths and the highly variable waiting time between outbreaks that are seen in the historical records of this species agree well with the predictions of the model. The thresholded resource-depletion dynamics result in substantial variation in the degree of periodicity between stochastic realizations. The completely aperiodic tree colonizations are partly predictable when the timing of the irregular windfall events are known. However, the predictability of inter-outbreak periods is low due to the large variation of cases falling most frequently in the middle between the extremes of purely nonperiodic (erratic) and periodic (cyclic) fluctuations.
Sammendrag
Bestanden av granbarkbillen viser en økende trend på Østlandet og i Trøndelag etter en periode med relativt lave nivåer i foregående år. Økningen kan ha sammenheng med en uvanlig god vekstsesong. I noen områder kan tidligere vindfellinger ha bidratt til å forsterke bestandsøkningen. Den ekstra store økningen i Østfold og Akershus kan muligens settes i sammenheng med at disse fylkene ligger nærmest til det svenske området hvor storstormen ”Gudrun” forårsaket voldsomme vindfellinger. Muligheten for effekter på tvers av landegrensene understreker behovet for samordning av barkbilleovervåkingene i Norge og Sverige, og dessuten behovet for beredskapsplaner om tilsvarende stormer skulle ramme vår del av Skandinavia.
Sammendrag
En ny barkbilleart Ips amitinus har vært påvist i importtømmer i 2002. Vi har studert muligheten for at denne arten kan bidra til hyppigere eller forsterkete barkbilleutbrudd i samspill med granbarkbillen. Undersøkelsen har benyttet modellsimuleringer, siden eksperimenter som kan øke risikoen for nyetableering ikke er akseptabelt. Simuleringene viser at denne nye arten under visse betingelser kan bidra til økt forekomst og intensitet av barkbilleutbrudd. Et føre var prinsipp tilsier at en bør søke å unngå at I. amitinus etableres i norske skoger. Funn av overvintrende individer av den nye arten på lagerplasser for importtømmer, samt innledende resultater fra en trinnvis importmodell, indikerer en stor risiko for at Ips amitinus kan spre seg og etablere seg i norsk skog. De innledende modellresultatene viser imidlertid også at det finnes mulige virkemidler for å dempe risikoen.
Sammendrag
Det er ikke registrert sammendrag
Sammendrag
Pulpwood has been imported to Norway since the beginning of the 20th century. However, exotic plant species hitchhiking with pulpwood were not observed before c.1985. Prior to this the imported timber was debarked, and the chances that diaspores would have attached to a debarked log (compared to a log with bark) are very small.A greenhouse germination experiment based on 385 dm2 of sifted bark from the holds of nine Estonian pulpwood ships yielded 3187 seeds of 201 species of vascular plants, few of which were typical of coniferous forests. Approximately 39% of the hitchhiking seeds did not germinate until after a period of cold treatment.Most of the species germinated in low densities, and those occurring in greater numbers are common and widespread in Norway. Six species were new to Norway: Agrostis clavata, Androsace filiformis, Bidens radiata, Carex montana, Melica picta, and Ranunculus cassubicus.During the last 20 years, pulpwood has been imported to Norway from many countries around the world, e.g. Russia, Scotland, Canada, and Zaire. While the present data do not indicate any immediate threat from aggressively invasive exotics, in order to avoid the introduction of non-native species and reduce the potential for biological invasion, timber should ideally be debarked prior to importation.
Sammendrag
Det er ikke registrert sammendrag
Sammendrag
Det er ikke registrert sammendrag
Sammendrag
Det er ikke registrert sammendrag
Forfattere
Paal KrokeneSammendrag
Bark beetles and associated phytopathogenic fungi elicit defence responses in conifers that may interfere with beetle establishment and development. Norway spruce is serving as a useful model species for studies of induced defences elicited by beetle attacks, fungal inoculation, and treatment with chemical elicitors.When trees are pretreated with a sublethal dose of fungal inoculations or with the phytohormone methyl jasmonate they become much more resistant to subsequent bark beetle attacks or artificial mass inoculations with fungi. This induced disease resistance follows dose-response dynamics, is nonspecific with respect to the pretreatment organism, appears to be nonsystemic, takes weeks rather than days to become activated, and can also be activated by mechanical wounding alone.Application of methyl jasmonate to Norway spruce stems induces a massive increase in terpene levels and external resin flow on the stem, whereas no increase is observed in soluble phenolics. Methyl jasmonate-application also leads to significantly less bark beetle colonization, with shorter parental galleries and fewer eggs laid in treated bark. There were also reductions in the number of beetles produced and the mean dry weight per beetle in methyl jasmonate-treated bark. Furthermore, fewer beetles were attracted to conspecifics tunneling in MJ-treated bark.The exact mechanisms responsible for induced resistance in Norway spruce and other conifers have not been determined, but inducible anatomical defense responses such as changes in polyphenol-containing parenchyma cells (PP cells) in the phloem and induction of traumatic resin duct formation in the sapwood seem to play an important role.
Sammendrag
When conifers such as Picea abies Karst. (Norway spruce) are attacked by insects or pathogens, they often respond by producing increased quantities of terpenoid oleoresin. This response can be mimicked in young P. abies seedlings by treatment with methyl jasmonate (MJ). In this study, we determined the effects of MJ on terpenoids and other chemical defenses of mature P. abies, and investigated whether this treatment protected trees against attack by the blue-stain fungus Ceratocystis polonica (Siem.) C. Moreau, the most important fungal associate of the spruce bark beetle Ips typo-graphus L. Methyljasmonate treatment induced the formation of traumatic resin ducts in the developing xylem, enhanced resin flow and stimulated increased accumulation of monoterpenes, sesquiterpenes and diterpene resin acids. However, only minor changes were detected in terpene composition in response to MJ treatment and no changes in soluble phenolic concentration were measured. There was much variability in the timing and degree of response to MJ among clones. The observed chemical and anatomical changes in response to MJ treatment were correlated with increased resistance to C. polonica, suggesting that terpenoid oleoresin may function in defense against this pathogen.