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.
2005
Forfattere
Bjørn ØklandSammendrag
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.
Sammendrag
Bland skalbaggarna finner vi en stor grupp (ca 1300 arter) som är beroende av dödved och bland dessa många rödlistade arter (418 arter). Många av arterna trivs i ekskog. Vilka faktorer bestämmer förekomst och artrikedom av dessa arter? Man kan tänka sig att det lokala skogsbeståndets eller nyckelbiotopens utseende är avgörande,men våra resultat pekar på att landskapet i större skala är viktigare för dessa djur, vilket har betydelse för naturvårdsstrategier.
Forfattere
Olavi Kurina Alexei Polevoi Frank Götmark Bjørn Økland Niklas Franc Björn Nordén Kjell HedmarkSammendrag
Det er ikke registrert sammendrag
Sammendrag
Det er ikke registrert sammendrag
Sammendrag
Det er ikke registrert sammendrag
Sammendrag
Det er ikke registrert sammendrag
Sammendrag
Sammendrag av foredrag som ble holdt på engelsk på et COST-møte om nyttenematoder i Italia i juni 2005. Foredraget tok for seg biologien til jordbærsnutebille og bringebærbille og så på mulighetene for å bekjempe dem med nematoder. Se engelsk versjon for mer informasjon
Sammendrag
In a survey in one conventional and four organic apple orchards in southeast Norway insect pathogenic fungi and parasitoids as natural enemies of green apple aphid (Aphis pomi) and rosy apple aphid (Dysaphis plantaginea) were studied weekly throughout the summer 2002 and 2003. Four species of insect pathogenic fungi in the order Entomophthorales were observed to infect both aphid species. These were Entomophthora planchoniana, Neozygites fresenii, Erynia neoaphidis and Conidiobolus obscurus. The highest fungal infection level in A. pomi was 39,6 % and 33,3 % in D. plantaginea. Neozygites fresenii was the fungal species being the most prevalent. This fungus also seemed to cause an epizootic in A. pomi and to decrease the aphid population in one organic location during the summer 2002. Parasitoids were a more important mortality factor in A. pomi than in D. plantaginea, and the highest parasitization recorded in A. pomi was 30 %. Four species of primary parasitoids hatched from A. pomi: Binodoxys angelicae, Lipolexis gracilis, Praon sp. and Ephedrus sp. Hyperparasitoids that hatched from A. pomi were Dendrocerus carpenteri, Alloxysta pleuralis, Phaenoglyphis villosa and Asaphes suspensus. Only one individual of D. plantaginea was parasitized and this parasitoid was Ephedrus persicae. Both fungi and parasitoids were abundant early in the season. The fungi were found from late June and throughout the season in some locations in 2002. Resting spores of N. fresenii were found in A. pomi in July. The parasitization showed two tops, one early in season (June/July) and one late in season July/August. Fungal infections were more prevalent than parasitoids in D. plantaginea. Fungi and parasitoids were equally important in A. pomi.
Sammendrag
The objective of this study was to examine the effects of increasing temperature (+2-2.5°C) and CO2 (370 ppm vs. 550 ppm) and 30% shading compared to outdoor conditions on autumn growth of a northern (63°N) and a southern (59°N) ecotype of Elymus repens (L.) Gould, Cirsium arvense (L.) Scop. and Sonchus arvensis L. Pieces of rhizomes (E. repens) and roots (C. arvense, S. arvensis) were planted in pots in May 2004 and grown outdoors at 58°N until the start of the experiment in September. The plants were cut to 20 cm height before start of experiment. Every fortnight developmental stage, leaf area, dry weight of above ground and belowground plant parts, and root/rhizome length were assessed. After cutting, E. repens regrew with new shoots and more leaf area until the end of the experiment, while S. arvensis withered shortly after the start of the experiment. C. arvense held an intermediate position with small regrowth on the existing shoots, while leaf area decreased. The southern ecotype of S. arvensis and C.arvense developed more roots than the northern ecotype with a corresponding lower shoot/root-ratio. The southern ecotype of C. arvense also produced more leaf area. The northern ecotype of E. repens developed more leaf area and shoot and root/rhizome dry weight. The leaf area and shoot dry weight averaged over all species, and the leaf area of E. repens and C. arvense increased with increasing temperature and shading. Elevated CO2 increased the leaf area of E. repens. Since the roots/rhizomes were little affected by changes in autumn climate, it is expected that next year"s infestation level is also not greatly influenced.
Sammendrag
Resultater fra forsøk i feltkammer der tilvekst om høsten og gjenvekst om våren er registrert.