Publikasjoner
NIBIOs ansatte publiserer flere hundre vitenskapelige artikler og forskningsrapporter hvert år. Her finner du referanser og lenker til publikasjoner og andre forsknings- og formidlingsaktiviteter. Samlingen oppdateres løpende med både nytt og historisk materiale. For mer informasjon om NIBIOs publikasjoner, besøk NIBIOs bibliotek.
2008
Forfattere
Arne SteffenremSammendrag
Wood based products come from a renewable resource playing an important part of the carbon cycle and are therefore regarded environmentally friendly compared to many other alternatives. We might therefore expect a more intensive use of the timber resource in the future. An increase in the supply and net value of timber products from a given area requires more intensive and cost efficient forest management. However, a faster growth rate in general and an increase in the juvenile wood proportion specifically, might come in conflict with the desirable wood quality. Tree breeding programs for Norway spruce (Picea abies L. Karst.) aim to follow up the general demands by providing forestry with plant materials that have superior growth and high wood quality. It is therefore important to establish a better knowledge of the potential of improving wood quality characters in this species through breeding. Characteristics important for structural strength and dimensional stability in conifers are wood density, spiral grain, microfibril angle (MfA) in the S2 layer in the secondary cell wall, branch characteristics and stem straightness. We have studied the genetic variation and correlation patterns for these traits and the direct end-use performance of clearwood samples in terms of stiffness (MOE) and strength (MOR) in four studies of Norway spruce (Paper I-IV). Wood quality traits of defect free wood were studied in Paper I and II. The materials used were 28 and 29 year old progeny trials planted in South East Norway on fertile soils. Significant genetic variation was found for wood density, MfA and spiral grain in both studies (p < 0.05). MOE and MOR, measured by static bending, were studied in one of the materials and the genetic variation was found to be highly significant (p < 0.01). There was also significant genetic variation (p < 0.05) in MOE estimated (MOEest) from wood density and the x-ray diffractometry pattern from the S2 layer obtained by SilviScan®-3. Genetic parameters were estimated in Paper II with large standard errors. The parameters must therefore be used with caution and preferably with support from other studies. We could confirm earlier studies of high genetic variation and low genotype by environment interactions (GxE) for wood density and spiral grain. Parameter estimates for MfA and MOEest, from one site, suggest that these are under moderate to strong genetic control in Norway spruce. Phenotypic correlations between growth traits (height and diameter growth) and wood quality traits were negative for wood density, positive for MfA and negative for MOEest. Genetic relationships showed the same trends for diameter growth, but not for height growth. The genetic and environmental variation in branch characteristics (Paper III and IV) were studied in three sets of progeny trials that were 22, 28 and 29 years old from planting. Stem straightness was studied in the 22-year old trial only. The branch diameter was highly influenced by site index and spacing. Number of branches formed and stem straightness seems to be under stronger genetic control. Individual tree heritabilities for growth traits, branch diameter and stem straightness were estimated in the 22-year old progeny trial planted at two sites. The trials were planted with different spacing, which allowed us to study genotype by spacing interactions. Heritability for growth traits and branch diameter across sites were moderate (0.14 - 0.19) compared to the higher values found for stem straightness (0.28). GxE, and thereby genotype by spacing interactions were not important for any of the traits. Heritability for number of branches, estimated from one of the sites, was 0.24. There was a strong and positive genetic correlation between growth traits and branch diameter. The presence of genetic variation for most wood quality traits suggests that these can be improved by tree breeding. However, genetic correlations with growth traits indicate that selection solely for growth might have adverse effects on wood quality. It is therefore important to balance the gain in growth and wood quality. Implementation of several adversely correlated traits in a breeding program reduces its efficiency. It is therefore essential that tree breeding, silvicultural practices and forest industrial needs interact when developing tree breeding programs to obtain an optimal strategy for selection and utilization of improved plant materials.
Sammendrag
In European forests, standings stocks are currently increasing and are higher than ever during the last decades. This is due to a multitude of reasons; human impacts such as reduced logging or the abandonment of agricultural land are clearly among them. However, data from intensive monitoring plots reveal an increased growth even in the absence of direct human intervention. For this study, we used a set of 363 such plots from 16 European countries, which are a subset of the ICP-Forests Level II plots, and are typically rectangular areas with a size of 0.25 ha. We investigated the influence of environmental factors on forest growth. In particular, the role of nitrogen, sulphur and acid deposition, temperature, precipitation and drought was elucidated. The study focussed on the tree species Norway spruce, Scots pine, common beech and European as well as sessile oak. We used existing information on site productivity, stand age and stand density to estimate expected growth. Relative tree growth was then calculated as the ratio between actual growth, obtained within a five years observation period, and expected growth. The site productivity incorporates past environmental conditions and was either computed from site index curves, where we distinguished Northern, Central and Southern Europe variants, or was taken from expert estimates. The models explained between 18% and 39% of the variance. Site productivity and stand age were positively and negatively related to actual growth, respectively. The results indicated consistently a fertilizing effect from nitrogen deposition, with roughly one percent increase in site productivity per kg of nitrogen deposition per ha and year, most pronounced for plots having soil C/N ratios above 25. We also found a positive albeit less clear relationship between relative growth and summer temperatures. Other influences were uncertain. In particular, we cannot conclude on detrimental effects on growth from sulphur and acid deposition or from drought periods.
Sammendrag
This paper reports the results from a study of modulus of elasticity (MOE) and modulus of rupture (MOR) of 42 small clear specimens prepared from 300 year old roundwood floor girders containing high levels of NaCl at Bryggen in Bergen, Norway. NaCl concentration was 6.5 % of the dry matter of the wood. MOE and MOR were 25 % lower than the values obtained from a reference material with equivalent annual ring width and density. The considerable reduction of MOE and MOR should be taken into consideration in conservation of load-bearing wooden structures that have been exposed to NaCl.
Sammendrag
Harmonization was achieved by carrying out joint sampling and assessment exercises at selected sites, inter-laboratory ring tests for the chemical analyses of deposition, plant and soil material, and by drawing up data compilation, data analysis and reporting guidelines and templates for the researchers working in the three countries.
Sammendrag
Insect-induced damages in forests are a major concern for timber production, landscape conservation and ecosystem research. Early detection methods based on remote sensing data can document the severity and spatial extent of ongoing attacks and might aid in designing mitigation measures or even prevention where necessary. In southeastern Norway, a large-scale insect defoliation of pine trees is ongoing. The larvae of the Pine sawfly Neodiprion sertifer reate it with its mass attacks during their feeding on needles in June and July. In the winter before the attack, egg galleries are evident in the needles. This provides a test case for early detection methods and remote sensing techniques for monitoring forest health....
Sammendrag
In Norway exterior wood structures have traditionally nearly exclusively been made of treated and untreated Picea abies and Pinus sylvestris. In recent years there has been a tendency that other tree species, like various domestic hardwoods and imported species have been used in exterior above ground applications, often unfinished. For several wood species, especially hardwoods, information regarding the durability in use class 3 is lacking. The main objective of this paper is to evaluate natural durability of Norwegian wood species for above ground applications comparing two non-standard above ground tests with the European standard tests for soil contact (EN 252) and lab performance against basidiomycetes (EN 113). The European standard tests EN 113 and EN 252 gave quite similar results, and they also corresponded well with the natural durability classification in EN 350-2. The two non-standard above ground tests differed to some extend from EN 113, EN 252 and EN 350-2. The results indicate that natural durability classification for one single wood species can change depending on use class. However, the field trials need a longer period of time before a final classification can be performed. Four species not included in EN 350-2 were classified in this study: Juniperus communis (1), Salix caprea (5), Sorbus aucuparia (5) and Populus tremula (5).
Sammendrag
Wood for outdoor decking has a high marked share in the Nordic and Baltic countries among private house owners. Important issues for the consumer are maintenance intervals and aesthetic appearance as well as decay resistance. Knowledge and consumer information about these aspects are required to ensure that wood can compete with alternative decking materials. In this paper an accelerated testing of decking, “stapelbäddsmetoden”, was evaluated after six years of exposure at Ås, Norway, and compared with earlier reported results after three years. Twelve different preservatives and wood modification treatments were used in addition to untreated Scots pine (sapwood and heartwood) and larch (heartwood). The samples were treated with two different surface treatments. In addition there was one set without any surface treatment. In this method for accelerated testing, discolouration and decay was evaluated. This provided new information about performance both on and above ground for a range of different combinations of preservative/modified systems and surface treatments of wood in decking for outdoor use. For example, no clear differences were found between the surface treatments and no surface treatment. The wood modifications with styrene and furfurylalcohol performed just as good, or better, than the copper containing treatments.
Sammendrag
Det er ikke registrert sammendrag
Sammendrag
In the last few decades, it has been noted that the epiphytic lichen Usnea longissima appears to be declining in numbers throughout its previous distribution range in Scandinavia. Up until now, clearcutting forestry has been considered the main threat to its persistence. Suspecting that other threats also may be at work, we studied the fate of 20 U. longissima localities in undisturbed forest stands, surveyed in 1994–95 and subsequently in 2003–04, in the Nordmarka region, north of Oslo, Norway. Yearly λ was calculated to be 0.94 (95% CI = 0.91-0.97), both with respect to number of trees bearing the lichen and total number of thalli per locality. This corresponds to a 10-year decline of 46%, or a half-life of 11 years. No new establishments were recorded. Now being listed as Endangered (EN) in the revised Norwegian Redlist of 2006, all known localities will be protected from major forestry operations. However, without knowledge of additional threat sources, its future possibility for survival looks bleak. Possible negative factors are discussed, including air pollution, increasing tree canopy closure, inter-specific competition, and genetic depauperation.
Sammendrag
Whereas lichen growth rates have received considerable attention, comparatively few detailed studies of growth patterns have been carried out. Generally, most lichens seem to grow apically, with pseudomeristomatic tissue confined to lobe margins and branch tips. However, some species appear to retain the capacity to expand throughout the thallus. Such intercalary growth processes have proved difficult to confirm in the field for two- and three-dimensionally growing folious and fruticose forms. Using transplants of the conspicuous, one-dimensionally growing Usnea longissima Ach., we document that intercalary growth actually does occur, with thalli expanding geometrically in length with a doubling time of less than a year under favorable conditions.