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.
2010
Forfattere
Stein Tomter Gro Hylen Jan-Erik Ørnelund NilsenSammendrag
Det er ikke registrert sammendrag
Sammendrag
Determining the feedbacks between terrestrial biosphere processes and the meteorological drivers (here precipitation and temperature) is crucial to ecosystem research. In this context, the continuous monitoring of the earth surface provides an invaluable basis for investigating the spatiotemporal dynamics in the activity of vegetation in relation to environmental conditions. Here, we seek to identify which patterns of variability in the meteorological drivers dominate the terrestrial photosynthetic activity from monthly to interannual time scales (resp. fluctuation frequencies). We investigate the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) using SeaWiFS observations from 1998 to 2005 and ancillary meteorological variables. A spectralanalysis leads to a global `classification` of the terrestrial biosphere according to prevalent scale dependent dynamics of fAPAR and its relation to the meteorology. A combined subsignal extraction and dimensionality reduction reveals a series of dominant geographical gradients on specific time scales. E.g. we uncover spatially coherent patterns at low frequencies and show where these are induced by precipitation or temperature fluctuations. We also show where high frequency variations (relative to the annual cycle) in fAPAR coincide with corresponding precipitation dynamics. However, we can also identify regions where the variability of fAPAR on specific time scales cannot be traced back to climate and is apparently shaped by other geoecological or anthropogenic drivers. http://www.terrabites.net/fileadmin/user_upload/terrabites/PDFs/Programme_Book_TERRABITES.pdf
Forfattere
Antti Asikainen Karl Stampfer Bruce TalbotSammendrag
Large volumes of spruce-dominated forests established on steep terrain are maturing in western Norway. The level of harvesting needed in utilising these forests calls for investments in cable yarding, processing and transport systems, and updated knowledge on the appropriate technology for Norwegian conditions. In the yarding-processing-truck transport operation, the processor cannot operate if the cable yarding system does not supply trees at a sufficient rate or when the buffer storage becomes full. As a result, the productivity of the whole system is often substantially lower than those of the individual parts in the system. Discrete-event simulation has been applied successfully in the analysis of a wide variety of wood harvesting and transport systems, where the productivities of different parts in the supply chain are interlinked .....
Forfattere
Bruce Talbot Nils Egil Søvde H. Fridén Lars WilhelmssonSammendrag
This paper builds on findings from the recently finalised work package 3.9 of the EU Indisputable Key project. Three institutes cooperated in developing intricate models spanning from the standing tree to the dispatch yard of a Swedish window manufacturer. Numerous timber properties were assigned to RFID tags, applied to the log at felling by a specially adapted harvester head. Logs were allocated to each of seven sawmills according to their timber properties using an LP based optimisation procedure. Simulation was then used to compare the fate of traced timber throughout the production lines of one of the sawmills and its downstream manufacturers.....
Sammendrag
Competition for canopy space is a fundamental structuring feature of forest ecosystems and remains an enduring focus of research attention. We used a spatial neighborhood approach to quantify the influence of local competition on the size of individual tree crowns in north-central British Columbia, where forests are dominated by subalpine fir (Abies lasiocarpa), lodgepole pine (Pinus contorta) and interior spruce (Picea glaucax engelmanii).Using maximum likelihood methods, we quantified crown radius and length as functions of tree size and competition, estimated by the species identity and spatial arrangement of neighboring trees.Tree crown size depended on tree bole size in all species. Given low levels of competition, pine displayed the widest, shortest tree crowns compared to the relatively long and narrow crowns found in spruce and fir. Sensitivity to crowding by neighbors declined with increasing tree height in all but the pine crown radius model. Five of the six selected best models included separate competition coefficients for each neighboring tree species, evidence that species generally differ in their competitive effects on neighboring tree crowns.The selected crown radius model for lodgepole pine, a shade-intolerant species, treated all neighbors as equivalent competitors. In all species, competition from neighbors exerted an important influence on crown size. Per-capita effects of competition across different sizes and species of neighbors and target trees varied, but subalpine fir generally displayed the strongest competitive effects on neighbors.Results from this study provide evidence that species differ both in their response to competition and in their competitive influence on neighbors, factors that may contribute to maintaining coexistence.
Sammendrag
In European forests, standing stocks are currently higher than ever during the last decades, in part due to reduced logging or the abandonment of agricultural land. However, data from intensive monitoring plots reveal an increased growth even without direct human intervention.We used a set of 363 plots from 16 European countries to investigate the influence of environmental factors on forest growth: nitrogen, sulphur and acid deposition, temperature, precipitation and drought, for 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, i.e., the ratio between actual growth within a five-year period and expected growth, was then related to environmental factors in a stepwise multiple regression.The results consistently indicate a fertilizing effect from nitrogen deposition, with roughly one percent increase in site productivity per kg of nitrogen deposition per ha and year, or 20 kg C fixation per kg N deposition. This was 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.From the study, we cannot conclude on any detrimental effects on growth from sulphur and acid deposition or from drought periods. A very recent study from the U.S., comprising 4800 plots and 24 tree species, confirms our results. However, we also show that the magnitude of N deposition effects on global forest C balance is currently a highly controversial matter, and comment on this debate. http://www.cef-cfr.ca/uploads/Colloque/Programme10_5.pdf
Forfattere
Svein Solberg Rasmus Astrup Dan Johan Weydahl Erik Næsset Terje Gobakken Ole Martin BollandsåsSammendrag
There is an increasing need for forest resource monitoring methods, as more attention is paid to deforestation, bio-energy and forests as habitats. Most national forest inventories are based on networks of field inventory plots, sometimes together with satellite data, and airborne laser scanning (ALS) is increasingly used for local forest mapping. These methods are expensive to establish or carry out, and many countries, including some severely affected by deforestation, do not apply such methods.Satellite based remote sensing methods in use today are hampered by problems caused by clouds and saturation at moderate biomass levels. Satellite SAR is not hampered by cloud problems, and monitoring of canopy surface elevation, which is correlated to key forest resource variables, might be a future method in forest monitoring.We here present the main findings of three studies (Solberg et al. 2010, a, b, c) investigating the potential of interferometric SAR (InSAR) for forest monitoring, by describing the relationship between InSAR height above ground and key forest variables. We based this study on InSAR data from the Shuttle Radar Topographic Mission (SRTM) with its acquisition in February 2000. We obtained SRTM InSAR DEM data from DLR for two forest areas in Norway, and built a ground-truth from the combination of field inventory and ALS.The forest areas were dominated by Norway spruce and Scots pine. In each forest area we laid out a number of field inventory plots, where we recorded standard forest variables such as Dbh and tree height, and from this derived plot aggregated variables of top height, mean height, stand density (mean tree height divided by the mean tree spacing), volume and biomass. We used this to calibrate and validate ALS based models, from which we derived estimates of the same variables for each SRTM pixel. This served as reference data for the SRTM data.From the X-band SRTM digital surface model (DSM) image we subtracted a high quality digital terrain model (DTM) derived from the ALS data. This was based on an extraction of ground echoes from the data provider, and the elevations of these echoes were interpolated into a grid fitting the SRTM grid.This produced data on the RADAR echo height above ground (InSAR height), which we related to the forest variables. With digital stand maps we aggregated the variables to the stand level. The X-band microwaves penetrate a little into the canopy, and the InSAR height was on average about 1.2 m below the mean tree height. InSAR height was strongly related to all forest variables, most strongly to top height.Particularly valuable was that stem volume and biomass, ranging up to 400 m3/ha and 200 t/ha, respectively, were linearly related to InSAR height with an accuracy, RMSE, of 19% at the stand level. However, these relationships had an intercept, which represents the microwave penetration into the vegetation, and due to this the relationships were non-linear for forest stands having heights and biomass values close to zero.With a lower quality DTM derived from topographic maps, the relationships were weaker. However, as long as a forest variable is within the ranges of the linear relationship, any change in InSAR elevation would be proportional to a change in forest height, volume or biomass. And, any logging should be detectable as a sudden decrease in InSAR elevation.Hence, a forest monitoring based on X-band InSAR might be suitable even without a DTM. An application of space borne InSAR for forest monitoring would be feasible for large areas at low cost, whereas an ALS acquisition for a part of the area would serve as reference data for calibration.
Sammendrag
Microbial disfigurement of coated wooden surfaces is considered a major maintenance concern and will shorten the aesthetic service life of wooden facades. The effect of the physical surface structure of a paint film when applied on wood may have an impact on the susceptibility to mould growth. Six model paints were formulated to give the following physical surface structures: glossy, matt, soft, hard, hydrophobic, and a film with air inclusion. The model paints and a standard paint, with and without fungicide, were applied on panels of Norway spruce (Picea abies L Karst.) and exposed outdoors for nearly three years according to a modified version of EN 927-3. A logistic regression model was fit to the data, and the degree of mould growth varied with exposure time and type of paint. Hard model paint was significantly more susceptible than the other model paints and had a performance close to the standard paint without fungicide. Soft model paint provided the best performance, with the least mould growth. Temperature, relative humidity, and precipitation did not significantly contribute to the model. (C) 2010 Elsevier Ltd. All rights reserved.
Sammendrag
While forest inventories based on airborne laser scanning data (ALS) using the area based approach (ABA) have reached operational status, methods using the individual tree crown approach (ITC) have basically remained a research issue. One of the main obstacles for operational applications of ITC is biased results often experienced due to segmentation errors. In this article, we propose a new method, called "semi-ITC" that overcomes the main problems related to ITC by imputing ground truth data within crown segments from the nearest neighboring segment. This may be none, one, or several trees. The distances between segments were derived based on a set of explanatory variables using two nonparametric methods, i.e., most similar neighbor inference (MSN) and random forest (RF). RF favored the imputation of common observations in the data set which resulted in significant biases. Main conclusions are therefore based on MSN. The explanatory variables were calculated by means of small footprint ALS and multispectral data. When testing with empirical data the new method compared favorably to the well-known ABA. Another advantage of the new method over the ABA is that it allowed for the modeling of rare tree species. The results of predicting timber volume with the semi-ITC method were unbiased and the root mean squared error (RMSE) on plot level was smaller than the standard deviation of the observed response variables. The relative RMSEs after cross validation using semi-ITC for total volume and volume of the individual species pine, spruce, birch, and aspen on plot level were 17, 38, 40, 101, and 222%, respectively. Due to the unbiasedness of the estimation, this study is a showcase for how to use crown segments resulting from ITC algorithms in a forest inventory context. (C) 2009 Elsevier Inc. All rights reserved.
Sammendrag
Scots pine (Pinus sylvestris) sapwood was investigated for variation in treatability using the wood modifying agent, furfuryl alcohol (FA) in water. The variation in treatability within trees, between trees and between different stands of Scots pine was studied. Investigated variables that reduced the residual variance significantly were: site location, latitude of site, height of trees, annual ring width, vertical and horizontal position in the tree and method of drying. Linear mixed model statistics were used and tree number was handled as a random variable. The best model reduced the treatability residual variance by 67%. Location was the single factor affecting treatability most. Differences in latitude between locations may be the reason for that. Latitude correlated negatively with the treatability. Within the trees, the treatability of sapwood increased with distance from ground and with distance from heartwood border. A small, but significantly better treatability was found for kiln dried wood (60A degrees C) compared to air dried wood (20A degrees C).