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.
2008
Authors
Erik LarnøyAbstract
To evaluate the decay resistance of wood, treated or untreated, for hazard classes 3, 4 and 5, the mass loss due to fungal exposure needs to be calculated. The standards for calculating mass loss in wooden test samples (i.e EN 113 and ENV 807) require that the samples used in the test are pre-dried to 0 % moisture content, m0, for determination of the initial dry mass. The standards describe that the samples should be dried at 103±2°C for 18 hours. When drying wood samples to 103 °C the samples are altered. Literature describes that extractives are influenced at temperatures as low as 60 °C, and redistribution and/or evaporation of these, will change the characteristics of the wood samples...
Abstract
The relationships between measures of forest structure as derived from airborne laser scanner data and the variation in quantity (Q) and vitality (V) of young trees in a size-diverse spruce forest were analyzed. A regeneration success rate (Q), leader length (V), relative leader length (V), and apical dominance ratio (V) were regressed against 27 different laser-derived explanatory variables representing three different spatial scales. The resulting 81 different models for each response variable were ranked according to their Akaike information criterion score and significance level. Each laser variable was then associated with four categories. These were scale, return, fraction, and type. Within the scale category, laser variables were grouped according to the spatial scale from which they originated. Similarly, within the return, fraction, and type categories, the variables were grouped according to if they originated from first or last return echoes; if they originated from lower, middle, or upper fraction of the range of laser heights or values derived from the full range of laser pulses, and if they were canopy height or canopy density metrics. The results show that the laser variables were strongest correlated with the quantity of small trees and that these variables could be attributed to large-scale, last return, lower fraction, and density metrics. The correlations with the vitality responses were weaker, but the results indicate that variables derived from a smaller scale than for the quantity were better in order to explain variation in leader length, relative leader length, and apical dominance ratio. (C) 2007 Elsevier B.V. All rights reserved.
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We investigated whether the stand age affects the life span of tree and understory fine roots (<1mm) in three Norway spruce (Picea abies) stands: 30, 60 and 120-yr-old. In each stand 9 minirhizotrons were installed and images were collected once in a month throughout the growing season during the three years. Norway spruce fine roots in the 30-yr old stand had a life span 401 ± 27 and 341 ± 68 days, and understory 409 ± 162 and 349 ± 142 days, estimated by using the Kaplan Meier survival analysis (KM) and Weibull distribution, respectively...
Authors
Peder GjerdrumAbstract
Moisture content, volatile in nature, is an important trait for any timber customer. Commercial board samples were observed to yield formulas for EMC reduction by kiln temperature, for hysteresis by board length, and for MC sorption dynamics by temperature. Industrial kiln practice lowers the EMC to approximately 95% of tabulated values. In this work, hysteresis was verified, and the most significant impact in natural ambient is that moisture migration to the board center appears to catch up with surface adsorption, reducing the influence of temperature and surface resistance. A concluding procedure for estimating MC dynamics for timber boards on stickers is outlined.
Authors
Peder Gjerdrum Olav Albert HøibøAbstract
A huge effort has been put into modelling wood quality the last few decades. Predicting knot size has been the centre of interest, either for timber quality, for tree growth models, or related purposes. The main objective of this paper is to analyse the stochastic features connected to knot distribution inside the three-dimensional volume of a tree\"s trunk. Four large Alpine spruce trees were sampled; age 150 years, DBH 30 to 70 cm, total volume 14.5 m3. To open a possibly large part of the stems, they were cross-cut to 31 logs and sawn to 193 unedged boards. On each unique board surface all perceptible knots were observed and localised in polar coordinates; origin in the stem base, along the pith and in the north direction. A total of 6200 knot intersections were observed in the 283 m2 sawn surfaces; however, most knots were observed several times in consecutive sawn surfaces. In order to obtain stationary variable, knot size was transformed by dividing by the square root of radial distance, and radial distance was transformed by dividing by log radius at the given location. Relative size, knot quality and spatial distribution were largely random and not correlated to each other in a tree. Thus, knots demonstrate a double nature, one part obeying the physiological laws, and another part stochastic.
Abstract
A Canadian model that simulates the course of frost tolerance in winter wheat under continental climatic conditions was adopted and further developed for use in an oceanic climate. Experiments with two cultivars were conducted during two winters in Central Norway. All plants were hardened at the same location. After hardening, in mid November, they were distributed to three locations with contrasting winter climates. Plants were sampled several times during autumn and winter and tested for frost tolerance, expressed as LT50 (the temperature at which 50% of the plants were killed). Results from the experiment were used in parameterization and cross validation of the new model, called FROSTOL, which simulates LT50 on a daily basis from sowing onwards. Frost tolerance increases by hardening and decreases by dehardening and stress, the latter caused by either low temperatures, or by conditions where the soil is largely unfrozen and simultaneously covered with snow. The functional relationships of the model are all driven by soil temperature at 2 cut depth. One of them is in addition affected by snow cover depth, and two of them are conditioned by stage of vernalization. Altogether five coefficients allotted to four of the functional relationships produced a good agreement (R-2 = 0.84) between measured and modelled values of LT50. A cross validation of the model indicated that the parameters were satisfactorily insensitive to variation in winter weather. (c) 2007 Elsevier B.V. All rights reserved.
Authors
Anne-Cathrine Scheen Charlotte Lindqvist Carl Gunnar Fossdal Victor A. AlbertAbstract
The five mint genera Brazoria, Macbridea, Physostegia, Synandra and Warnockia (Lamioideae: Lamiaceae) are all North American endemics. Together with the monotypic European genus Melittis and the Asian genus Chelonopsis, these taxa have been classified as subtribe Melittidinae. Previous morphological studies have failed to uncover synapomorphic characters for this group.We sequenced the plastid trnL-trnF region and trnS-trnG spacer and the nuclear ribosomal 5S non-transcribed spacer (5S-NTS) to assess phylogenetic relationships within Melittidinae. Standard parsimony and direct optimization (POY) analyses show Melittis, the type genus of the subtribe, as sister to Stachys. Thus, the monophyly of subtribe Melittidinae is not supported either by molecular or morphological data...
Abstract
The root-rot causing fungus Heterobasidion annosum sensu lato is the most devastating pathogen of conifers in Europe. This pathogen enters Norway spruce through the roots and can colonize the tree from within, growing as a saprophyte when established within the dead heartwood and acting as a necrotroph when in contact with living host tissue. Despite the high incidence of damage, trees have defences against this pathogen in the bark and living wood. Furthermore, spruce has a defense against internal attack by forming a reaction zone, in this case the host defense is directed inwardly by the still living sapwood toward the central colonized heartwood. We have studied the host responses to infection in Norway spruce clones at the transcriptional level and found that the speed of recognition and that spatial defense signalling appears to be the hallmarks of trees with high degree of resistance...