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
Lukas Gudmundsson Holger LangeSammendrag
Many time series analysis methods depend on equally spaced observations with no data point missing. If this condition is met, powerful techniques are available that identify temporal structures such as trends, periodic phenomena or nonlinear dynamics. Unfortunately, most observations of natural systems, in particular over longer periods of time such as decades, are prone to sampling errors leading to missing points in the observations. Singular System Analysis (SSA) is a powerful tool to extract the dynamics contained in time series at arbitrary temporal scales. In its original formulation, however, SSA relies as well on data without missing values. Recently several extensions to SSA have been proposed which are designed to fill the gaps, exploiting the dynamics contained in the sampled parts of the series to estimate the structure of the signal at the position of missing values. SSA consists of two steps: Decomposition and reconstruction. For the decomposition the time series under investigation is embedded into a trajectory matrix and decomposed with singular value decomposition. The reconstruction (of selected components) of the time series employs the left and right singular values to obtain additive components of the time series. In the original variant of SSA both steps are dependent on gap free data sets. In order to evaluate the power of SSA for time series with missing values we simulate 1000 series of different processes - ARMA(2,3) and red noise contaminated sine waves. Several gap–schemes (continuous, periodic, and uniformly distributed) are used to create time series with up to 50% (artificially) missing values. SSA is applied on all surrogate series. The decomposition as well as the reconstruction is compared systematically to the gap free benchmark. In addition we evaluate the ability of SSA to capture periodic phenomena in the presence of missing values and whether periodical gaps lead to the identification of spurious periods. We demonstrate that SSA successfully reproduces the signal part of time series (i.e. components with large eigenvalues) for up to 30% missing values. For less significant components with higher rank numbers, the presence of gaps is increasingly deleterious. A number of distributed smaller gaps, a situation most likely to occur in observations, spoils the analysis to a much lesser degree than a single large gap. Thus, these new variants of SSA substantially enlarge the set of observational time series amenable to the analysis, and allows for obtaining precise estimates of the signal at the position of missing data points.
Forfattere
Tor Håkon SivertsenSammendrag
Climate change scenarios provide alternative plausible future climate for the planet, each being an example of what might happen under a particular set of assumptions. Scenarios are not specific predictions or forecasts. Scenarios provide starting points for examining questions about the uncertain future climate.Some of the main processes connected to exchange of energy of the atmosphere of the planet usually are connected to radiation of short wave and long wave electromagnetic radiation. The global albedo of the short wave radiation is one important parameter, and the processes connected of the greenhouse gases water vapour and carbon dioxide in the atmosphere are extremely important elements of future scenarios.The total amount of output of fossil carbon into the atmosphere is of importance as well as the natural cycle of the carbon. Also there exist several important positive feedback systems. The amount of water vapor in the atmosphere is connected to the temperature of the air, or to be more specific the saturation vapour pressure of the water in the air is increasingly dependent on the temperature of the air. Usually a warm atmosphere then will contain more water vapour than a cold atmosphere, and this will make the atmosphere even warmer because water vapour is the most important greenhouse gas connected to long wave radiation.The ice cover of the Arctic and Antarctic regions as well as the glaciers in the high mountainous areas on the Earth are important for keeping the albedo of the short wave radiation of globe high. When the glaciers and the ice cover are melting, the albedo is decreasing and the consequence seems to be even more melting of ice.The ultimate worst case scenario seems to be that the ice cover and the glaciers of the planet melt down and the oceans receive all this water. The present situation seems to be like this:The total energy of short wave radiation, received by the planet: 100 unitsPlanetary albedo: 30%Total energy connected to the water cycle. 21 unitsAmount of yearly precipitation totally: 1000mmAverage residence time of a water molecule in the atmosphere: 10 daysTotal volume of ice on the planet: 33 x 106 km3 (~ 60 m of sea level equivalent)Total amount of CO2 in the atmosphere: 385 ppmIn order to understand the content and the challenge of the different scenarios I would like to know the value of the following parameters (every 5th year) of the scenarios:AlbedoTotal energy connected to the water cycleAmount of yearly precipitation totallyAverage residence time of a water molecule in the atmosphereTotal mass of ice on the planetTotal amount of CO2 in the atmosphere
Sammendrag
Manipulation of the canopy cover and site preparation are the most important silvicultural measures to enhance the conditions for natural regeneration of Norway spruce (Picea abies (L.) Karst.). During the early regeneration phase however, seedling mortality may be high, so it is important to study how different combinations of stand-level treatments and site preparation methods affect seedling establishment. We studied emergence, 1st winter and 2nd summer mortality for naturally regenerated spruce seedlings in a field experiment that combined four harvest treatments (shelterwoods of high (SH), medium (SM) and low (SL) residual basal area, and a 50 x 50 m clear-cut (CC)) and two site preparation methods (patch scarification and inverting). The CC had significantly fewer seedlings the 1st fall than the SL and SH (p = 0.0377), and in all harvest treatments, fewer seedlings emerged in inverted than in patch scarified spots (p = 0.0351). Mortality was also lower with patch scarification than inverting (1st winter: p = 0.0565, 2nd summer: p = 0.0377), but was not affected by harvest treatment (1st winter: p = 0.9211, 2nd summer: p = 0.1896). On average, mortality from 1st to 2nd fall reached 38% and 27% after inverting and patch scarification, respectively. First winter mortality accounted for approximately two thirds of the accumulated mortality, regardless of the harvest treatment and site preparation method.
Sammendrag
The environmental control of flowering in five populations of Fragaria virginiana ssp. glauca and three populations of F virginiana ssp. virginiana (henceforth referred to as F virginiana), obtained as seed from the National Plant Germplasm Repository, Corvallis, OR, USA, has been studied under controlled environment conditions. Except for the F virginiana ssp. glauca population PI 551648 from the Wasatch Mountains in Utah, which was truly day-neutral across a 9 degrees - 27 degrees C temperature range, all the other populations of both sub-species behaved as quantitative (facultative) short-day (SD) plants with earlier and more abundant flowering under SD than under long-day (LD) conditions. Flowering of the remaining F virginiana ssp. glauca populations was governed by a significant interaction of photoperiod and temperature. The SD dependence for flowering increased with increasing temperature from 9 degrees C to 27 degrees C. The optimum temperature for the SD flowering response was 15 degrees - 21 degrees C. While SD promotion of flowering was more pronounced in the F virginiana populations, temperature had no significant main effect on flowering in this sub-species, demonstrating a wide temperature tolerance for flowering. Vigorous runner formation was observed in all populations, in both SD and LD, with a highly significant advancement effect of increasing temperature. The flowering and runnering responses of these E virginiana populations are discussed in relation to their putative paternity of perpetual-flowering F. X ananassa cultivars. It is concluded that, with the complex inheritance in these octoploid plants, the flowering responses of the populations studied here are not reflected in the LD flowering response of cultivated everbearing strawberries.
Sammendrag
This paper discusses the monitoring network for diffuse pollution from agriculture in Estonia in the context of implementation of the EU Water Framework Directive (WFD) and the Nitrate Directive (ND). Seven surface water monitoring stations in agricultural catchments represent two out of three river basin districts designated in Estonia according to the WFD criteria. The national monitoring programme of ground water quality involves 516 stations of which about half were monitored in 2005. The monitoring sites cover all main ground water bodies in Estonia but are largely concentrated in the Nitrate Vulnerable Zone (NVZ). Analyses did not reveal any significant trends in total nitrogen (TN) and total phosphorus (TP) concentrations in studied rivers during the last 15 years except in one site. The ground water quality stabilised after decrease of nitrate concentrations in the early 1990s, especially in the south part of the NVZ, but even in 2005 the nitrate concentration exceeded 50 mg l1 in 42 out of 145 ground water samples in this region. The existing surface water quality monitoring network provides only restricted information to select between different management options when implementing action programmes for the NVZ and the river basin management plans (RBMP) under the WFD.
Forfattere
Thomas Hartnik Line Sverdrup John JensenSammendrag
lpha-cypermethrin, a synthetic pyrethroid, is used as an insecticide in agricultural settings, and increasingly replaces organophosphates and carbamates due to lower application rates and lower mammal toxicity. As very little is known about the acute and chronic toxicity for soil living organisms, this study investigated acute and sublethal toxicity of alpha-cypermethrin for four terrestrial invertebrate species in an agricultural soil from Norway. Bioassays with the earthworm Eisenia fetida, the potworm Enchytraeus crypticus, the springtail Folsomia candida and the land snail Helix aspersa were performed according to slightly modified versions of OECD- or ISO-guidelines and resulted in median lethal concentrations (LC50) of >1000 to 31.4 mg/kg and sublethal no-effect-concentrations (NOEC) of 2.51 to 82 mg/kg. A high acute-to-chronic ratio (ACR) was found in especially the earthworms. Interspecies differences in sensitivity may be explained by differences in exposure and differences in metabolisation rate. When based on measured pore water concentrations, terrestrial species appear overall to be about one order of magnitude less sensitive than aquatic species. Effect assessments conducted according to European guideline for risk assessment of pesticides reveal that assessments based on acute toxicity tests are not always conservative enough to warrant environmentally safe concentrations in soil. Mandatory incorporation of sublethal toxicity data will ensure that also in regions with temperate climate effects of pesticides on populations of soil living organisms are unlikely.
Forfattere
Abdelhameed Elameen Siri Fjellheim Arild Larsen Odd Arne Rognli Leif Sundheim Susan Msolla Esther Masumba Kiddo Mtunda Sonja KlemsdalSammendrag
Sweet potato (Ipomoea batatas L.) is the fifth most important crop in the developing countries after rice, wheat, maize and cassava. The amplified fragment length polymorphism (AFLP) method was used to study the genetic diversity and relationships of sweet potato accessions in the germplasm collection of Sokoine University of Agriculture, Morogoro and Sugarcane Research Institute, Kibaha, Tanzania. AFLP analysis of 97 sweet potato accessions using ten primer combinations gave a total of 202 clear polymorphic bands. Each one of the 97 sweet potato accessions could be distinguished based on these primer combinations. Estimates of genetic similarities were obtained by the Dice coefficient, and a final dendrogram was constructed with the un-weight pair-group method using arithmetic average. AFLP-based genetic similarity varied from 0.388 to 0.941, with a mean of 0.709. Cluster analysis using genetic similarity divided the accessions into two main groups suggesting that there are genetic relationships among the accessions. Principal Coordinate analysis confirmed the pattern of the cluster analysis. Analysis of molecular variance revealed greater variation within regions (96.19%) than among regions (3.81%). The results from the AFLP analysis revealed a relatively low genetic diversity among the germplasm accessions and the genetic distances between regions were low. A maximally diverse subset of 13 accessions capturing 97% of the molecular markers diversity was identified. We were able to detect duplicates accessions in the germplasm collection using the highly polymorphic markers obtained by AFLP, which were found to be an efficient tool to characterize the genetic diversity and relationships of sweet potato accessions in the germplasm collection in Tanzania.
Sammendrag
Vegetation fire is the worldwide disturbance that affects the largest area and biggest biomes variety. Fire instantaneously generates large C fluxes to the atmosphere, as gas and soot particles. In the same time, part of ecosystem organic matter (OM) is converted into charred material that may contribute to the stable pool of soil organic carbon (SOC). The net effect of vegetation fire on C sequestration remains uncertain because the two major impacts operate at very different timescales and C budget is highly dependent on ecosystem and fire conditions. The aim of the present research was to assess fire-induced C fluxes to the atmosphere and as new litter and charcoal production during a prescribed fire in a subtropical oak shrub. Pre-fire biomass and post-fire charred and unburned biomass were determined for vegetation leaves and stems, litter and soil in 20 sub-plots installed in a 30-ha area prescribed for fire. Concentrations of C were determined, and fluxes among pools and to the atmosphere were derived from these measurements. In a first assessment, charred OM was visually identified in standing biomass and litter using its black and shiny aspect. In a second step, a strong chemical oxidation with K2Cr2O7/H2SO4 was used to isolate only a highly recalcitrant part of pyrogenic C. After the fire, standing dead biomass was only composed of stems with charred surface. The leaves transferred from vegetation to litter during the fire represented more than a half of post-fire litter. Percentage of initial C pool that was lost to the atmosphere as gas or particles was 55 % from vegetation stems, 80 % from vegetation leaves, and 70 % from litter. Soil C stocks were not significantly modified by fire, in agreement with moderate temperature elevation in the soil proper. Total C release to the atmosphere, including gas and particles, was 2.6 kg C m"2. Visually-identified charcoal represented 5% of remaining stem C (i.e. 60 g C m"2) and 21% of post-fire litter C (i.e. 80 g C m"2). The stem and litter charcoal contained 4±4 % and 16±5 % of highly recalcitrant C, respectively. We assessed that a typical scrubland fire may add between 10 and 140 g C m"2of chemically stable pyrogenic C to the soil. The conversion rate of ecosystem C to chemically stable pyrogenic C would be between 0.2 and 3.4 %.
Forfattere
Øyvind Nordli Frans-Emil Wielgolaski Anne Kjersti Bakken Stein Harald Hjeltnes Finn Måge Anders Sivle Oddvar SkreSammendrag
Data series for bud burst, beginning of flowering and petal fall for 20 species of deciduous trees and conifers at four sites in different regions of southern Norway have been analysed and related to temperature series. On average, the spring phenophases occurred 7 days earlier during the period 1971–2005. The most significant linear trends were observed for the earliest phases. The trends in this period were compared with trends in other periods, the longest one starting in 1927. Those starting in cold decades and ending in 2005 were in most instances statistically significant, whereas hardly any significant trend appeared for series starting in warm decades. This fact showed that the results of trend studies are very sensitive to the choice of starting year. There were significant decadal variations in 40% of the series. The dates of occurrence of the phenophases, varying from the first days of May to the first days of June, correlated with seasonal temperature series, in most cases strongest to mean temperatures for the seasons March–May and April–May. The North Atlantic Oscillation Index (NAOI) for January and February appeared to have some predictive power for the date of occurrence of the recorded phases. The basis for this may be that the oscillations described by the index are of importance for the fulfilment of physiological chilling requirements needed to break bud dormancy. The same genotypes of the trees were grown in region West Norway and in Central Norwegian region; during the period 1965– 2005 the trends towards earlier bud burst were more pronounced and steeper at the western site.
Sammendrag
1. Results for Cornell University, New York: The optimal pH for velvet bentgrass was around 5.0, but velvet bentgrass was not sufficiently wear tolerant at an annual input of only 0.75 kg N/100m2/yr 2. Report from Rutgers University, New Jersey: The recuperative potential of velvet bentgrass is considered poor, but our findings have shown that the wear tolerance of velvet bentgrass is just as high as for creeping bentgrass and that the high density of velvet bentgrass will restrict Poa annua encroachment under trafficked conditions 3. Bosch & Mitowski 2006 Master thesis, University of Rhode Island : - Greenwich provides better turf quality than Avalon - More than 2.0 kg N/100 m2/ yr necessary to produce acceptable quality of on USGA greens - Around 3.0 kg N/100 m2/ yr may be necessary to produce acceptable quality on straight sand greens in regions with 6-7 months growing period". However, lower N-rates may be acceptable with the use of iron, especially at high pH. - Topdressing and vertical mowing had little effect in this 2 yr study, but in general, velvet bentgrass greens seems to need vertically mowing and topdressing at least one a month to avoid soft and "puffy" greens Statement: "The common perception that velvet bentgrass is a low maintenance species may not always be true, at least not on sandy greens". 4. Irrigation research, Rutgers University, New Jersey: The water consumption increased in the order velvet bent