Publikasjoner
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2010
Forfattere
Svein SolbergSammendrag
Four alternative airborne laser scanning (ALS) canopy penetration variables were compared for their suitability for mapping of gap fraction, leaf area index and disturbances in a Scots pine forest. The variables were based on either echo counting or intensity, and on either first or first and last echoes. ALS data and field-measured gap fraction and effective leaf area index (LAIe) were gathered before and after a severe insect defoliation by pine sawflies. LAIe is a commonly used form of leaf area index that is mathematically derived from gap fraction, and includes the areas of foliage, branches and trunks, and which is not corrected for the clumping of foliage. The ALS penetration variables were almost equally strongly related to field-measured gap fraction and LAIe. The estimated slopes in the LAIe models varied from 0.94 to 2.71, and had coefficient of determination R 2 values of 0.92–0.94. They were strongly correlated to each other (R 2 values of 0.95–0.98) and agreed fairly well for temporal changes of LAIe during the summer and the insect defoliation (R 2 values of 0.82–0.95). Counting of first and last echoes produced penetration rates close to the gap fraction, and this penetration variable was able to penetrate tree crowns. Ground-only echoes represented mostly between-tree gaps, and canopy-first-ground-last pulses represented mostly within-canopy gaps. However, the penetration variables based on first and last echoes suffered from the problem that a second echo might be impaired both in low and in tall canopies. In low canopies, two adjacent echoes from the same pulse would be too close in time to be separated by the sensor, while in tall canopies the pulse might apparently be fragmented down through the canopy. The intensity-based penetration variables needed to be supplemented with reflectance values, or at least the ratio between reflectance of the canopy and the ground, and this ratio was estimated from the data. The study demonstrated that one might be able to distinguish between disturbance types, e.g. between defoliation and cutting, by comparing alternative ALS penetration variables. Insect defoliation was dominated by an increase in within-canopy gaps and, correspondingly, the fraction of partly penetrating canopy-first-ground-last pulses. Tree removals from cutting were dominated by increases in between-tree gaps and the corresponding fraction of ground-only pulses.
Sammendrag
The primary aim of this study was to investigate the suitability of interferometric X-band SAR (InSAR) for inventory of boreal forest biomass. We investigated the relationship between SRTM X-band InSAR height and above-ground biomass in a study area in southern Norway. We generated biomass reference data for each SRTM pixel from a field inventory in combination with airborne laser scanning (ALS). One set of forest inventory plots served for calibrating ALS based biomass models, and another set of field plots was used to validate these models. The biomass values obtained in this way ranged up to 250 t/ha at the stand level. The relationship between biomass and InSAR height was linear, no apparent saturation effect was present, and the accuracy was high (RMSE = 19%). The relationship differed between Norway spruce and Scots pine, where an increase in InSAR height of 1 m corresponded to an increase in biomass of 9.9 and 7.0 t/ha. respectively. Using a high-quality terrain model from ALS enabled biomass to be estimated with a higher accuracy as compared to using a terrain model from topographic maps. Interferometric X-band SAR appears to be a promising method for forest biomass monitoring. (C) 2010 Elsevier Inc. All rights reserved.
Sammendrag
Le gel printanier peut etre dommageable pour les semis de Picea abies (L.) Karst. nouvellement plantes si leur rythme de croissance n'est pas suffisamment adapte aux conditions climatiques de la station forestiere. Les objectifs de cette etude consistaient a determiner de quelle facon le debourrement et la resistance au gel printanier sont influences par un traitement de jours courts (JC) appliques a differents moments et avec differents regimes de temperature durant la periode de formation des bourgeons. A la suite d'un entreposage hivernal, la resistance au gel a ete evaluee apres une, trois et cinq semaines dans des conditions de forcage. Le traitement JC a avance le debourrement comparativement aux semis temoins. Par comparaison, le moment du traitement et les differentes temperatures ont eu peu d'effet sur le debourrement. Le traitement JC a augmente la resistance au gel des aiguilles d'un an pendant la periode de desendurcissement. Applique tot, le traitement JC a augmente la resistance au gel des aiguilles d'un an et le diametre au collet comparativement a une application plus tardive. Il est important que la periode de noirceur atteigne une duree critique lorsque le traitement JC prend fin pour eviter une deuxieme eclosion des bourgeons. Des temperatures basses a la suite du traitement JC ont augmente la resistance au gel des aiguilles et diminue celle de la tige. Les effets contraires de la temperature sur differents tissus vegetaux demontrent l'importance d'examiner differents tissus apres des essais de gel-degel. Spring frost may result in detrimental damage in newly planted Picea abies (L.) Karst. seedlings if their growth rhythm is not sufficiently adapted to the climatic conditions on the forest site. The aims of this study were to evaluate how bud break and spring frost hardiness were influenced by short-day (SD) treatments with different timing and different temperature regimes during bud formation. Following winter storage, frost hardiness was tested after 1, 3 and 5 weeks in forcing conditions. The SD treatment advanced bud break compared with the control seedlings. In comparison, the effects of timing and the different temperatures on bud break were small. The SD treatment improved frost hardiness in first-year needles during dehardening. The early SD treatment resulted in improved frost hardiness in first-year needles and greater root collar diameter compared with later SD treatment. To avoid a second bud flush, it is important that a critical night length is attained when the SD treatment terminates. Low temperatures following the SD treatment resulted in increased hardiness of the needles and decreased hardiness of the stems. The contrasting effect of temperature in different plant tissues demonstrates the importance of examining different tissues following freezing tests.
Sammendrag
The suitability of interferometric X-band radar for forest monitoring was investigated. Working in a spruce-dominated forest in southeast Norway, top height, mean height, stand density, stem volume, and biomass were related to space shuttle interferometric height above ground. A ground truth dataset was produced for each radar data pixel in the study area by combining a field inventory and automatic tree detection with airborne laser scanning data. Pixels were aggregated to forest stands. Interferometric height was strongly related to all of the five forest variables, and most strongly to top height with R-2 = 0.71 and RMSE = 13% at the pixel level and R-2 = 0.82 and RMSE = 5.6% at the stand level. Interferometric height was linearly related to stem volume and biomass up to 400 m(3)/ha and 200 t/ha, respectively, and RMSE was approximately 19% for both variables. These errors contain error components caused by the 3.5-year time lag between the radar acquisition and the laser scanning. It is concluded that interferometric X-band radar has potential for use in forest monitoring.
Sammendrag
Development in surface mould growth on painted/unpainted wooden claddings and acting climatic factors were investigated over a period of 3 years. Eight wood substrates, including modified, preservative-treated and untreated wood, were tested in combination with three types of paint: (1) water-borne alkyd modified acrylic paint without fungicide; (2) solvent-borne alkyd paint without fungicide; and (3) ICP (internal comparison product). One set of samples was exposed unpainted. The samples were tested according to a modified version of EN 927-3. A logistic regression model was fitted to the data. The degree of mould growth varied with exposure time, coating typology, wood substrate, temperature and relative humidity. Exposure time and coating typology contributed most to the model. After 3 years of outdoor exposure unpainted panels and panels coated with solvent-borne paint without fungicide had more mould growth than panels coated with ICP and water-borne paint without fungicide. Unpainted oil/copper–organic preservative-treated claddings had higher resistance to mould growth than other unpainted wood substrates. Coated untreated pine and coated acetylated pine were more susceptible to mould growth than other coated wooden substrates.
Sammendrag
During the first few weeks of life, chicks of the capercaillie (Tetra urogallus) and black grouse (T. tetrix) subsist mainly on insects, of which lepidopteran and hymenopteran larvae are the main components. We studied the breeding phenology of these two species and examined how the timing of breeding was related to the temporal distribution of their larval food source. During a five-year survey, capercaillie mated and hatched consistently four to six days before black grouse. Depending on the vegetation type, the number of larvae (>= 2 mm in length) increased between five and ten times within 10 days, and hatching coincided roughly with the peaks in larval numbers. Due to body growth, however, larval abundance in terms of volume was reached later and occurred 8-9 and 13-14 days after the mean hatching dates in the two species, respectively. Slightly later development of Hymenoptera as compared with that of Lepidoptera contributed in extending the period of high larval abundances for more than one week. The timing of breeding of the two species appears, therefore, to match the temporal distribution of insect food for the fast-growing chicks as they hatch several days before the peak in larval volumes. In one year, when mating was advanced, presumably due to exceptionally warm weather before mating (yet the temporal abundance of larvae was unchanged), breeding success was higher than in years when mating occurred later.
Forfattere
Mari Mette TollefsrudSammendrag
Det er ikke registrert sammendrag
Forfattere
Mari Mette TollefsrudSammendrag
Det er ikke registrert sammendrag
Forfattere
Mari Mette TollefsrudSammendrag
Det er ikke registrert sammendrag
Forfattere
Mari Mette TollefsrudSammendrag
Det er ikke registrert sammendrag