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.
2013
Sammendrag
The mating system ofCapercaillie has been referred to as “exploded lek” because displaying males are spaced farther apart than on classical leks. However, inter-male distances and spacing behavior rarely have been quantified. In 2009–2011, we examined the spatial relationships of males on two leks in southeastern Norway by GPS satellite telemetry. Largely exclusive display territories (median 2 ha) surrounded the mating site, but the males spent most of the time displaying on smaller, well-defined display sites (median 182 m2) within their territories. When on their display sites, neighboring birds were spaced 64–212 m apart; decreasing to a minimum during the time of mating. Occasionally, males made long exploratory excursions (median 243 m) across the territories of neighbors, sometimes interacting with them at close distance (< 10m). During daytime, males resided solitarily in radially extending ranges within 1 km of the lek center, commuting to the lek either in the evening or morning by walking or flying, leaving in the morning mostly by walking. The distance from the lek center to night roosting trees and daytime resting areas decreased during the mating season. With interacting males and a spatial arrangement in-between that of classical leks and dispersed polygyny, the term “exploded lek” seems appropriate for the mating system of Capercaillie.
Sammendrag
Rot fungi are a major problem in the construction sector, and method to study under which moisture and temperature coefficients they grow are therefore of significant interest. Measurements of heat production rate have been made on wood samples with the brown rot fungus Postia placenta at different moisture contents (MCs). The results clearly show the heat production rate (ameasure of respiration rate and fungal activity) is moisture-dependent. For most cases, less heat was produced when the MC was decreased, and more heat was produced when the MC was increased. It was also found that when the MC increased after a dry period, the increase in activity was significantly delayed. However, if the moisture state was then kept constant at a high level, the activity slowly increased, showing that the fungi need time to recover back to the original activity level after drying. Isothermal calorimetry is a measurement technique well suited for the study of the activity of wood-decaying fungi as a function of temperature and moisture content.
Forfattere
Lars Qviller Nina Risnes Olsen Kim Magnus Bærum Erling Meisingset Leif Egil Loe Bjørnar Ytrehus Hildegunn Viljugrein Atle MysterudSammendrag
Det er ikke registrert sammendrag
Sammendrag
Modelling stem taper and volume is crucial in many forest management and planning systems. Taper models are used for diameter prediction at any location along the stem of a sample tree. Furthermore, taper models are flexible means to provide information on the stem volume and assortment structure of a forest stand or other management units. Usually, taper functions are mean functions of multiple linear or nonlinear regression models with diameter at breast height and tree height as predictor variables. In large-scale inventories, an upper diameter is often considered as an additional predictor variable to improve the reliability of taper and volume predictions. Most studies on stem taper focus on accurately modelling the mean function; the error structure of the regression model is neglected or treated as secondary. We present a semi-parametric linear mixed model where the population mean diameter at an arbitrary stem location is a smooth function of relative height. Observed tree-individual diameter deviations from the population mean are assumed to be realizations of a smooth Gaussian process with the covariance depending on the sampled diameter locations. In addition to the smooth random deviation from the population average, we consider independent zero mean residual errors in order to describe the deviations of the observed diameter measurements from the tree-individual smooth stem taper. The smooth model components are approximated by cubic spline functions with a B-spline basis and a small number of knots. The B-spline coefficients of the population mean function are treated as fixed effects, whereas coefficients of the smooth tree-individual deviation are modelled as random effects with zero mean and a symmetric positive definite covariance matrix. The taper of a tree is predicted using an arbitrary number of diameter and corresponding height measurements at arbitrary positions along the stem to calibrate the tree-individual random deviation from the population mean estimated by the fixed effects. This allows a flexible application of the method in practice. Volume predictions are calculated as the integral over cross-sectional areas estimated from the calibrated taper curve. Approximate estimators for the mean squared errors of volume estimates are provided. If the tree height is estimated or measured with error, we use the “law of total expectation and variance” to derive approximate diameter and volume predictions with associated confidence and prediction intervals. All methods presented in this study are implemented in the R-package TapeR.
Sammendrag
Fine roots contribute to net primary production in forests, but knowledge of fine root longevity and turnover is still incomplete and limited to few tree species. In this study, we used minirhizotrons to compare fine root biomass, longevity and turnover of Pinus sylvestris L., Betula pendula Roth and Picea abies (L) Karst. in southern Sweden. Minirhizotron tubes were installed in 2006 and root images were taken in 2007–2010. Soil cores were used to estimate fine root biomass. Soil samples were taken from the humus layer and from 0 to 10 cm, 10 to 20 cm and 20 to 30 cm depth in the mineral soil. Only images from the humus layer and the upper 10 cm of mineral soil were included in root analysis. Spruce has a higher aboveground production than pine and birch in southern Sweden and this was reflected in larger fine root biomass as well as higher fine root biomass production. The annual tree fine root biomass production (humus and 0–30 cm in mineral soil) was 73, 78 and 284 g m−2 in pine, birch and spruce stands, respectively. Thicker fine roots tended to live longer. The majority of the fine roots were thinner than 0.5 mm in diameter, with a turnover rate (KM) of 0.4 year−1. When comparing all fine roots, i.e. all roots 0–2 mm, pine had the highest longevity, 1120 days, compared with 900 days for spruce and 922 days for birch (KM).
Sammendrag
To better understand the historic range of variability in the fire regime of Fennoscandian boreal forests we cross-dated 736 fire scars of remnant Scots pine (Pinus sylvestris L.) wood samples in a 3.6 km2 section of the Trillemarka-Rollagsfjell Reserve of south-central Norway. Using a kernel range application in GIS we spatially delineated 57 individual forest fires between 1350 and the present. We found a strong anthropogenic signal in the fire regime from 1600 and onwards: (i) infrequent variably sized fires prior to 1600 shifted to frequent fires gradually decreasing in size during the 1600s and 1700s, with only a few small fires after 1800; (ii) time intervals between fires and the hazard of burning showed substantial differences pre- and post-1600; (iii) fire seasonality changed from late- to early-season fires from the 1626 fire and onwards; and (iv) fire severity decreased gradually over time. Written sources corroborated our results, narrating a history where anthropogenic forest fires and slash-and-burn cultivation expanded with the increasing population from the late 1500s. Concurrently, timber resources increased in value, gradually forcing slash-and-burn cultivators to abandon fires on forest land. Our results strengthen and expand previous Fennoscandian findings on the anthropogenic influence of historic fire regimes.
Sammendrag
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Sammendrag
When calculating the Bandt and Pompe ordinal pattern distribution from given time series at depth D, some of the D! patterns might not appear. This could be a pure finite size effect (missing patterns) or due to dynamical properties of the observed system (forbidden patterns). For pure noise, no forbidden patterns occur, contrary to deterministic chaotic maps. We investigate long time series of river runoff for missing patterns and calculate two global properties of their pattern distributions: the Permutation Entropy and the Permutation Statistical Complexity. This is compared to purely stochastic but long-range correlated processes, the k-noise (noise with power spectrum f−k), where k is a parameter determining the strength of the correlations. Although these processes closely resemble runoff series in their correlation behavior, the ordinal pattern statistics reveals qualitative differences, which can be phrased in terms of missing patterns behavior or the temporal asymmetry of the observed series. For the latter, an index is developed in the paper, which may be used to quantify the asymmetry of natural processes as opposed to artificially generated data.
Sammendrag
An 11-year remotely sensed surface albedo dataset coupled with historical meteorological and stand-level forest management data for a variety of stands in Norway’s most productive logging region is used to develop regression models describing temporal changes in forest albedo following clear-cut harvest disturbance events. Datasets are grouped by dominant tree species, and two alternate multiple regression models are developed and tested following a potential-modifier approach. This result in models with statistically significant parameters (p < 0.05) that explain a large proportion of the observed variation, requiring a single canopy modifier predictor coupled with either monthly or annual mean air temperature as a predictor of a stand’s potential albedo. Models based on annual mean temperature predict annual albedo with errors (RMSE) in the range of 0.025–0.027, while models based on monthly mean temperature predict monthly albedo with errors ranging between of 0.057–0.065 depending on the dominant tree species. While both models have the potential to be transferable to other boreal regions with similar forest management regimes, further validation efforts are required. As active management of boreal forests is increasingly seen as a means to mitigate climate change, the presented models can be used with routine forest inventory and meteorological data to predict albedo evolution in managed forests throughout the region, which, together with carbon cycle modeling, can lead to more holistic climate impact assessments of alternative forest harvest scenarios and forest product systems.
Sammendrag
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