Paal Krokene
Research Professor
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Min CVBiography
I study plant-insect interactions, and particularly how conifers defend themselves against bark beetles and fungi. The work is highly interdisciplinary and I collaborate with chemists, molecular biologists and ecologists at NIBIO and abroad. The methods we use span from field experiments to chemical ecology and molecular biology. I have worked at NIBIO since 1992. I studied at the University of Oslo, where I graduated as Master of Science in ecology / entomology in 1992 and Dr. Scient. (PhD) in forest entomology in 1996. Since 2004, I have been an adjunct professor at the Norwegian University of Life Sciences (NMBU), where I teach forest entomology. Since 2018, I am also a member of the Plant Health Panel of the Norwegian Scientific Committee for Food and Environment (VKM).
Authors
Tao Zhao Suresh Ganji Christian Schiebe Björn Bohman Philip Weinstein Paal Krokene Anna-Karin Borg-Karlson C. Rikard UneliusAbstract
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Abstract
submittedVersion
Abstract
The purpose of this study is to increase the basic understanding of outbreak dynamics in order to improve the management of bark beetle outbreaks. The spruce bark beetle Ips typographus is a major disturbance agent of European forests and is the continent’s most economically and environmentally damaging bark beetle. Outbreaks of the spruce bark beetle are often triggered by large windfall episodes, and we have utilized a unique opportunity to study a Slovakian outbreak where little salvage logging was performed in some areas after a 2.5 million m3 storm-felling in 2004. Our analyses focused on the first five years after the windfall, and we used a combination of empirical data and simulation models to understand the spatial patterns of beetle-killed forest patches developing during the outbreak. The univoltine beetle population used an increasing proportion of the windfelled trees during the two first seasons after the storm, but from the third season onwards our comparisons of inter-patch distance distributions indicated a transition from beetle production largely in windfall areas to a self-sustaining outbreak with infestation patches developing independently of the windthrows. The size of new infestation patches formed after this transition was modeled as a function of beetle pressure, estimated by the proportion of a circle area surrounding new patches that was covered by infestation patches the previous year. Our model results of patch size distribution did not correspond well with the empirical data if patch formation was modeled as a pure dispersal–diffusion process. However, beetle aggregation on individual trees appears to be important for patch development, since good correspondence with empirical data was found when beetle aggregation was incorporated in the modeled dispersal process. The strength of correspondence between the beetle aggregation model and the empirical data varied with the density of aggregation trees in the modeled landscape, and reached a maximum of 83% for a density of three aggregation trees per infestation patch. Our results suggest that efficient removal of windfelled trees up until the start of the second summer after a major windfall is important to avoid a transition into a patch-driven bark beetle outbreak that is very difficult to manage. Our results also indicate that the outcome of a patch-driven outbreak is difficult to predict, since the development of new infestation patches is not a simple function of beetle pressure but is also affected by beetle behavior and local forest conditions.
Authors
Paal KrokeneAbstract
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Abstract
Overvåkingsprogrammet, som er finansiert av Mattilsynet, undersøkte i 2025 om karanteneskadegjøreren furuvednematode (Bursaphelenchus xylophilus) var til stede i hogstavfall fra furu eller i furubukker av slekten Monochamus, kjent som vektorer for B. xylophilus. I programmets delaktivitet som omfattet kartlegging av furuvednematode i hogstavfall ble det tatt 404 flisprøver fra hogstavfall og vindfall av furu (Pinus sylvestris) med tegn på angrep av furubukker i slekten Monochamus. Prøvene ble tatt i Akershus, Innlandet og Østfold. Flisprøvene ble inkubert ved 25 °C i to uker, før nematoder ble ekstrahert med Baermann-trakt og undersøkt i mikroskop. Furuvednematoden B. xylophilus ble ikke påvist, men den naturlig forekommende arten Bursaphelenchus mucronatus kolymensis ble oppdaget i åtte flisprøver. Siden overvåkingen av furuvednematode startet i 2000, har alle de 10 141 analyserte flisprøvene vært negative for furuvednematode. I programmets delaktivitet som omfattet kartlegging av furuvednematode i furubukker ble feller med kjemiske attraktanter for fangst av voksne, flygende furubukker satt opp nær vareimportsteder i Akershus, Oslo, Vestfold, Rogaland og Trøndelag. Ingen Monochamus-biller ble fanget, noe som kan tyde på at varer importert til de overvåkte importstedene ikke inneholdte levende Monochamus-biller. Fraværet av Monochamus-biller i fellene tyder også på at det var lite naturlig hjemmehørende Monochamus-biller i overvåkingsområdene.
Abstract
Dette overvåkings- og kartleggingsprogrammet er finansiert av Mattilsynet og arbeidet er utført av Norsk institutt for bioøkonomi (NIBIO) og Mattilsynet. Formålet er å så tidlig som mulig oppdage fremmede og skadelige trelevende insektarter som måtte ankomme Norge. Beredskapsdelen av prosjektet inkluderer et lett tilgjengelig lager av feller og kjemiske lokkemidler til bruk dersom utvalgte karanteneskadegjørere skulle bli oppdaget. De ulike lokkemidlene som brukes i prosjektet tiltrekker seg biller i slektene Anoplophora og Agrilus, samt flere andre bark- og trelevende insektarter på EPPO (European and Mediterranean Plant Protection Organization) sine lister over karanteneskadegjørere. Sommeren 2025 ble fire lokkemidler testet i feller ved bruk av en fangstmetodikk etablert i 2021. Fellene var utplassert i skogområder nær åtte ulike virksomheter som var vurdert av Mattilsynet å ha forhøyet risiko for å introdusere fremmede arter. Totalt ble det fanget 5 616 trelevende insekter. Det ble ikke fanget noen karanteneskadegjørere.
Authors
Maarten de Groot Tine Hauptman Kristjan Ait Flavius Bălăcenoiu Eckehard G. Brockerhoff Luka Capuder Gyorgy Csoka Mirza Dautbasic Massimo Faccoli Juraj Galko Jean Claude Grégoire Jaroslav Holuša Mats Jonsell Boris Hrašovec Hervé Jactel Magdalena Kacprzyk Urs Kamm Markus Kautz Maartje J. Klapwijk Marija Kolšek Paal Krokene Diana Marčiulynienė Markus Melin Marton Paulin Milan Pernek Jason Sumner-Kalkun Floor Vodde David Williams Tiina Ylioja Gernot HochAbstract
In the last few decades, bark beetle outbreaks have increased in European forests, triggered by extreme weather events, such as drought and windstorms. A core element of integrated pest management to control outbreaks are salvage logging and sanitation felling, i.e., the timely removal or treatment of potential brood material and already infested trees after disturbance events. Associated with these management operations as well as with regular, planned thinning and cutting, felling residues, such as treetops, branches and stumps that remain in the forest provide potentially suitable breeding material for bark beetles and may trigger further outbreak events. Although felling residue management is part of regular forest management in most of Europe, no overview exists on its use throughout the continent. To fill this gap, we gathered forest health experts from 20 European countries and used a questionnaire to provide information on felling residue management in the context of forest protection in managed forests. Relevant legislation in these countries was reviewed for regulations concerning this topic. We found that most countries have felling residue management in their legislation and/or perform it in practice. In 12 of the 20 countries, felling residue management is being applied to manage bark beetles, particularly in areas that have experienced large-scale outbreaks in the last few decades. Felling residues are mainly managed in forests dominated by Norway spruce ( Picea abies L. Karst) and pines ( Pinus spp.) (in 19 and 17 of the countries, respectively). The most frequently used management methods on a European level were piling or mulching of felling residues. These methods were used in 14 and 16 of the countries, respectively. Besides bark beetle management, use of residues for bioenergy (4 countries) and biodiversity conservation (6 countries) was reported. The diversity of felling residue management practices across Europe may reflect differences in forest policies and climatic gradients that are affecting bark beetle outbreak risks. This overview presents the variety of felling residue management applied across 20 European countries, highlighting the reasons for and implications of its use, as well as further research needs.