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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.

2011

Abstract

Small dimensions regenerated forests are considered a useful fuel resource for small local heat plants in Norway, since it is not relevant for the timber industry. Most small heat plants built so far are constructed for moisture contents of about 35% on wet basis. Therefore, the material must be dried. Because artificial drying induces additional costs, storing the material in piles roadside as whole trees until desired moisture content is obtained is considered beneficial. Traditionally, leaf seasoning has been considered an efficient method. To increase the understanding of these processes, a study on drying whole trees in piles has been accomplished at three different locations with different climatic conditions. The study focuses on the following explanatory variables: harvesting season, location, climatic conditions, position in the pile, tree species, and relative crown length. The effect of covering the piles in order to reduce the moisture uptake during winter was also studied. Models, estimating the moisture content with time profiles, were developed. During spring and summer the moisture content was reduced to approximately 35% also when the material was harvested in the autumn the year before. The climatic conditions were important for the drying result, but drying was effective also in the moist climate in western Norway. Covering the dry piles before the winter was important in order to maintain the requested moisture content. The effect of covering the material harvested in autumn was limited.

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Abstract

The Eurasian spruce bark beetle, Ips typographus, is one of the major forest insect pests in Europe, capable of mass-attacking and killing mature Norway spruce trees. The initiation and development of a new generation are strongly controlled by temperature and a warmer climate may affect the number of generations that is produced per year and hence the outbreak dynamics. Experimental knowledge regarding reproductive diapause adaptations is, however, too sparse for largescale assessments of future trends. We developed a model description of diapause induction, and used gridded observational temperature data to evaluate multiple combinations of day length and temperature thresholds to find the model parameterisation most coherent with I. typographus monitoring data from Scandinavia. The selected model parameterisation is supported by European literature data, though further experimental studies are required to analyse population specific adaptations and capacity for adjustments to changing climate conditions. Implementing the model description of reproductive diapause in a temperature driven model of bark beetle phenology (swarming activity and development from egg to mature bark beetle), enabled us to assess the length of the late summer swarming period that is a critical determinant of the risk of forest damage. By using regional climate model data we show that higher temperatures can result in increased frequency and length of late summer swarming events, producing a second generation in southern Scandinavia and a third generation in lowland parts of central Europe. Reproductive diapause will not prevent the occurrence of an additional generation per year, but the day length cues may restrict the length of the late summer swarming period.