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.
2004
Abstract
Conventional extreme value statistics and the calculation of return periods implicitly assume stationarity of distributions and statistical independence at least asymptotically (most extreme events).We demonstrate, using a collection of river runoff time series from Southern Germany, that these assumptions are invalid, and that temporal as well as spatial correlations prevail instead: temporal differences of distributions are nearly synchronized within a region, and there are systematic trends of percentiles especially at low flow conditions within the 20th century.As a consequence, the estimated return periods of a given threshold flow are fluctuating, in some cases even in a dramatic fashion. On the other hand, a general trend towards an increase in flood frequencies cannot be stated on basis of our investigations, in accordance with other recent findings (Mudelsee et al. 2003), but contrary to general expectations drawn from climate change studies.
Authors
Per Holm NygaardAbstract
No abstract has been registered
Authors
Ole K. Hansen Ulrik Bräuner Nielsen Øyvind Meland Edvardsen Brynjar Skulason Jan-Ole SkageAbstract
In three Nordic field trials, 26 provenances of Abies lasiocarpa (Hook.) Nutt. and Abies lasiocarpa var. arizonica (Merriam) Lemmon were evaluated 3 yrs after establishment. The focus was on 16 traits important for adaptation, establishment and production of Christmas trees.For all three sites in Denmark, Norway and Iceland, survival ranged from 89 to 96%. Provenances showed statistically significant differences for all but two traits. For all traits there was significant interaction between provenance and site. Analysis of ecovalens showed that for most traits, only a limited number of provenances contributed substantially to the interaction. Therefore, a large proportion of the provenances showed a fairly consistent ranking across sites.The frequency of potential Christmas trees in the provenances ranged from 10 to 49%. Southern provenances from New Mexico and Arizona seemed to have the best potential for producing high-quality Christmas trees. The southern provenances added substantially to the interaction between provenance and site for budset, lammas growth and colour. When using multivariate statistical methods on all measured traits, the provenance clusters fitted neatly into six distinct geographical regions.
Abstract
Artikkelen drøfter saltinnhold i ulike bygningsdeler i Bryggen i Bergen, saltets opphav og betydning i forhold til bevaring av trevirket. Ulike nedbrytningsorganismer i saltholdig tømmer er også vurdert.
Abstract
Using Singular System Analysis (SSA), we extract a collection of significant long-term components (with dominant periods of at least 3 years) for a large number of river runoff records.At first glance, these long-term modes are a distinct feature of this variable, not contained in precipitation and temperature, and not easily correlated to commonly known long-term indices (NAO, SOI, NHT, SUN, etc.). However, low-pass filtered versions of these time series exhibit strikingly similar behavior, like common maxima, within a region (such as Southern Germany), pointing to a common origin.Although not an unequivocal example for synchronization, we quantify the degree of synchronization as a function of the regional extent of the data and propose a mechanism, stochastic resonance, discussed in climate dynamics, which is able to produce this collective behavior despite the lack of deterministic drivers. We also comment on air pressure-induced teleconnections between the different large scale oscillations in the climate system.
Authors
Morten Eikenes Per Otto Flæte Erlend Ystrøm Haartveit Stig LandeAbstract
Wood modification based on furfuryl alcohol improves several important wood properties, such as the resistance to fungal decay and insect attack, hardness, dimensional stability, bending strength and stiffness. The improvements of wood properties depend on the weight percent gain (WPG) due to furfurylation.Fourier transform near infrared (FT-NIR) spectroscopy was used to calibrate PLS-regression models for prediction of WPG due to furfurylation in birch wood. Spectra were obtained in cross-sections of solid wood. A PLS-regression model based on wood samples with WPG ranging from 16.7 to 35.1%, performed well when validated on a separate test set.The coefficient of determination between laboratory measured WPG and predicted WPG was high (R2 = 0.87). The prediction error given by the root mean square error of prediction was low (RMSEP = 1.23). The results showed that the technique should be considered a prospective tool for quality assessment of furfurylated wood.
Authors
Tonje Økland Vegar Bakkestuen Rune Halvorsen Økland Odd EilertsenAbstract
Question: Does the understorey vegetation of Norwegian boreal forests change in relation to broad-scale, long-term changes? Location: Norway. Methods: Permanently marked 1-m2 vegetation plots from 17 monitoring reference areas in forests dominated by Picea abies (11 areas, 620 plots) and Betula spp. (six areas, 300 plots) were analysed twice, at the start in 1988-1997 and 5 yr later (1993-2002). Species subplot frequency data were analysed separately for each area by univariate and multivariate statistical methods; 5-yr changes in single species abundances, species number per plot and species composition were tested. Results: Two distinct patterns of change were found: Abundance of several vascular plant species decreased in SE Norwegian Picea forests, most noticeably of species with a preference for richer soils, such as Oxalis acetosella. Abundance of many bryophyte species as well as bryophyte species number per plot increased in forests of both types over most of Norway. Conclusions: The pattern of vascular plant changes is probably a time-delayed response of long-lived, mainly clonal, populations to acidified soils resulting from deposition of long-distance airborne pollutants. The pattern bryophyte changes, with reference to the close link between climatic conditions for growth and abundance changes for Hylocomium splendens established in previous demographic studies, is related to climatic conditions favourable for bryophyte growth. We conclude that many forest understorey plants are sensitive indicators of environmental change, and that the concept used for intensive monitoring of Norwegian forests enables early detection of changes in vegetation brought about by broadscale, regional, impact factors.
Abstract
In this study modified linseed oils, rape oil and three waxes were screened on their efficacy as wood protecting agents. By testing all products when impregnated with high retentions in Scots Pine sapwood on water repellence qualities, additionally an accelerated weathering test, drying quality, accelerated brown rot and blue stain test, an indication is formed of the capability of these products as wood protecting treatments. All oil and wax treatments significantly improve the water repellency of untreated wood. In weathering resistance, maleinised and polymerised linseed oil showed the best results in improving untreated pine sapwood dimensional stability thus reducing crack formation and decolourization by UV-light. In accelerated brown rot and blue stain tests boiled linseed oil significantly reduced degradation and staining. In addition, maleinised linseed oil and a mixture of modified linseed- and mineral oil are very well performing in the blue stain test. Overall most promising products are the maleinised oils and boiled linseed oil. The maleinised oils have good potentials in long lasting water repellency, showed some fungal growth prevention, are colour stable in weathering tests and create a dimensional stable wood product. Boiled linseed oil is not exceptionally good as a water repellent, but the good drying qualities together with easy handling makes this oil a promising product.
Abstract
The process of model building in the environmental sciences and when dealing with ecosystems is discussed. Two types of modeling approaches need to be distinguished: An algorithmic one, which has been used traditionally in physics, meteorology, and other branches where biological degrees of freedom are either absent or neglectable; and an interactive one, which is a new framework in computer science and seems to be most suitable in cases where organisms (including humans) as agents in ecosystems are to be taken into account. The first modeling approach is exemplified by state models in dynamic systems theory and expresses the correspondence imposed by Natural Law between inferential entailment in a formal system and causal entailment in natural systems. Modeling is to be separated from simulation. Simulation is a less restrictive type of modeling in which the description of non-interactive behaviour is the purpose and no constraints on the correspondence to internal states are imposed. The second (new) modeling approach is exemplified by interactive simulation models. It is able to express the correspondence in behaviour imposed by engineering standards (or cultural norms in general) between documentation, training and application in interactive choice situations such as games or ecosystem management. It generalises the notion of simulation for interactive problems. In an idealised situation the strictest correspondence between behaviour in a natural and a virtual system is expressed as bisimulation. The principles for model building are shortly demonstrated with examples.
Authors
Peder GjerdrumAbstract
With wood, the moisture content is an intrinsic volatile property - constantly changing in accordance to the environment. For the efficient use of timber, knowledge about the MC is increasingly being requested, and the sawmill being required to reveal such information. This paper presents an algorithm for estimating, on a weekly basis, the running MC and MC variation of a timber lot. Input variables are the MC of the lot when leaving the kiln, storage condition and running weather observations. The model, described in mathematical terms, is valid for timber stored on stickers, i.e. under homogeneous air circulation, and meant for implementation in the sawmill’s MPS.