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Erik Christiansen

Bio: Erik Christiansen is an academic researcher from Forest Research Institute. The author has contributed to research in topics: Bark beetle & Picea abies. The author has an hindex of 29, co-authored 42 publications receiving 4745 citations. Previous affiliations of Erik Christiansen include Institut national de la recherche agronomique.

Papers
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Journal ArticleDOI
TL;DR: This review focuses on bark defenses, a front line against organisms trying to reach the nutrient-rich phloem, and questions about their coevolution with bark beetles are discussed.
Abstract: Conifers are long-lived organisms, and part of their success is due to their potent defense mechanisms. This review focuses on bark defenses, a front line against organisms trying to reach the nutrient-rich phloem. A major breach of the bark can lead to tree death, as evidenced by the millions of trees killed every year by specialized bark-invading insects. Different defense strategies have arisen in conifer lineages, but the general strategy is one of overlapping constitutive mechanical and chemical defenses overlaid with the capacity to up-regulate additional defenses. The defense strategy incorporates a graded response from 'repel', through 'defend' and 'kill', to 'compartmentalize', depending upon the advance of the invading organism. Using a combination of toxic and polymer chemistry, anatomical structures and their placement, and inducible defenses, conifers have evolved bark defense mechanisms that work against a variety of pests. However, these can be overcome by strategies including aggregation pheromones of bark beetles and introduction of virulent phytopathogens. The defense structures and chemicals in conifer bark are reviewed and questions about their coevolution with bark beetles are discussed.

929 citations

Journal ArticleDOI
TL;DR: Experimental studies in the Pacific Northwest and the southeast U.S.A., and in Norway, are drawn upon to show that tree resistance to attack may be closely related to the amount of current and stored photosynthate that is available for defense.

479 citations

Book ChapterDOI
01 Jan 1988
TL;DR: The spruce bark beetle, Ips typographus Linnaeus (Coleoptera: Scolytidae), is the most destructive scolytid in the coniferous forests of the palaearctic region.
Abstract: The spruce bark beetle, Ips typographus Linnaeus (Coleoptera: Scolytidae), is the most destructive scolytid in the coniferous forests of the palaearctic region. In Europe, outbreaks may lead to the destruction of millions of Norway spruces [Picea abies (Linnaeus) Karsten], its principal host tree. In Northeastern Asia a subspecies, Ips typographus Linnaeus f. japonicus Niijima, may cause severe damage to spruces in the group P. jezoensis (Siebold and Zuccarini) Carriere sensu lato.

249 citations

Journal ArticleDOI
TL;DR: Wounding of Norway spruce by inoculation with sterile agar, or agar containing the pathogenic fungus Ceratocystis polonica, induced traumatic resin duct formation in the stem, which may represent a defense mechanism in NorwaySpruce against the pathogens fungus.
Abstract: Wounding of Norway spruce by inoculation with sterile agar, or agar containing the pathogenic fungus Ceratocystis polonica, induced traumatic resin duct formation in the stem. Visible anatomical responses occurred in the cambium 6-9 d post-inoculation. Near the inoculation site cellular proliferation, polyphenolic accumulation, and lignification were induced as a wound reaction to seal the damaged area. Five centimetres from the inoculation site cells in the cambial zone swelled and divided to form clusters. By 18 d post-inoculation, these cells began to differentiate into resin duct epithelial cells surrounding incipient schizogenous lumens. Mature axial traumatic ducts appeared by 36 d as a row of ducts in the xylem centripetal to the cambium. The ducts formed an interconnected network continuous with radial resin ducts. Parenchyma cells surrounding the ducts accumulated polyphenols that disappeared as the cells differentiated into tracheids. These polyphenols appeared to contain fewer sugar residues compared to those accumulating in the secondary phloem, as indicated by the periodic acid-Schiff's staining. The epithelial cells did not accumulate polyphenols but contained immunologically detectable phenylalanine ammonia lyase (EC 4.3.1.5), indicating synthesis of phenolics as a possible resin component. These findings may represent a defense mechanism in Norway spruce against the pathogenic fungus Ceratocystis polonica.

239 citations

Journal ArticleDOI
TL;DR: In this article, a balanced experiment based on 20 field plots located in a 21 km 2 Scots pine forest in southeast Norway covering age classes from newly regenerated to old forest, leaf area index (LAI) was determined in field by a LAI-2000 instrument and hemispheric photography.

235 citations


Cited by
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Journal ArticleDOI
TL;DR: A conceptual model of the evolution of plant defense is concluded, in which plant physioligical trade-offs interact with the abiotic environment, competition and herbivory.
Abstract: Physiological and ecological constraints play key roles in the evolution of plant growth patterns, especially in relation to defenses against herbivores. Phenotypic and life history theories are unified within the growth-differentiation balance (GDB) framework, forming an integrated system of theories explaining and predicting patterns of plant defense and competitive interactions in ecological and evolutionary time. Plant activity at the cellular level can be classified as growth (cell division and enlargement) of differentiation (chemical and morphological changes leading to cell maturation and specialization). The GDB hypothesis of plant defense is premised upon a physiological trade-off between growth and differentiation processes. The trade-off between growth and defense exists because secondary metabolism and structural reinforcement are physiologically constrained in dividing and enlarging cells, and because they divert resources from the production of new leaf area. Hence the dilemma of plants: Th...

3,843 citations

Journal ArticleDOI
TL;DR: A hydraulically based theory considering carbon balance and insect resistance that allowed development and examination of hypotheses regarding survival and mortality was developed, and incorporating this hydraulic framework may be effective for modeling plant survival andortality under future climate conditions.
Abstract: Summary Severe droughts have been associated with regional-scale forest mortality worldwide. Climate change is expected to exacerbate regional mortality events; however, pre- diction remains difficult because the physiological mechanisms underlying drought survival and mortality are poorly understood. We developed a hydraulically based theory considering carbon balance and insect resistance that allowed development and examination of hypotheses regarding survival and mortality. Multiple mechanisms may cause mortality during drought. A common mechanism for plants with isohydric

3,302 citations

Journal ArticleDOI
TL;DR: In this article, applied linear regression models are used for linear regression in the context of quality control in quality control systems, and the results show that linear regression is effective in many applications.
Abstract: (1991). Applied Linear Regression Models. Journal of Quality Technology: Vol. 23, No. 1, pp. 76-77.

1,811 citations

Journal ArticleDOI
TL;DR: It is striking how phylogenetically distant organisms have come to use similar structures for common purposes in terpenes, and new natural roles undoubtedly remain to be discovered for this large class of compounds.
Abstract: As the largest class of natural products, terpenes have a variety of roles in mediating antagonistic and beneficial interactions among organisms. They defend many species of plants, animals and microorganisms against predators, pathogens and competitors, and they are involved in conveying messages to conspecifics and mutualists regarding the presence of food, mates and enemies. Despite the diversity of terpenes known, it is striking how phylogenetically distant organisms have come to use similar structures for common purposes. New natural roles undoubtedly remain to be discovered for this large class of compounds, given that such a small percentage of terpenes has been investigated so far.

1,602 citations

Journal ArticleDOI
TL;DR: In this article, a conceptual framework using one system as a model, emphasizing interactions across levels of biological hierarchy and spatiotemporal scales is presented, and the dynamics are bidirectional as landscape features influence how lower-scale processes are amplified or buffered.
Abstract: Biome-scaledisturbancesbyeruptiveherbivoresprovidevaluableinsightsintospeciesinteractions,ecosystemfunction,andimpactsof globalchange. We present a conceptual framework using one system as a model, emphasizing interactions across levels of biological hierarchy and spatiotemporal scales. Bark beetles are major natural disturbance agents in western North American forests. However, recent bark beetle population eruptions have exceeded the frequencies, impacts, and ranges documented during the previous 125 years. Extensive host abundance and susceptibility, concentrated beetle density, favorable weather, optimal symbiotic associations, and escape from natural enemies must occur jointly for beetles to surpass a series of thresholds and exert widespread disturbance. Opposing feedbacks determine qualitatively distinct outcomes at junctures at the biochemical through landscape levels. Eruptions occur when key thresholds are surpassed, prior constraints cease to exert influence, and positive feedbacks amplify across scales. These dynamics are bidirectional, as landscape features influence how lower-scale processes are amplified or buffered. Climate change and reduced habitat heterogeneity increase the likelihood that key thresholds will be exceeded, and may cause fundamental regime shifts. Systems in which endogenous feedbacks can dominate after external forces foster the initial breach of thresholds appear particularly sensitive to anthropogenic perturbations.

1,561 citations