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.
2009
Sammendrag
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Sammendrag
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Forfattere
Svein Solberg Mathias Dobbertin Gert Jan Reinds Holger Lange Kjell Andreassen Paloma Garcia Fernandez Anders Hildingsson Wim de VriesSammendrag
Det er ikke registrert sammendrag
Forfattere
Svein Solberg Andreas Brunner Kjersti Holt Hanssen Holger Lange Erik Næsset Miina Rautiainen Pauline StenbergSammendrag
In this study we demonstrate how airborne laser scanning (ALS) can be applied to map effective leaf area index (LAI(e)) in a spruce forest, after being calibrated with ground based measurements. In 2003 and 2005, ALS data and field estimates of LAI(e) were acquired in a Norway spruce forest in SE Norway. We used LI-COR's LAI-2000 (R) Plant canopy analyzer ("LAI-2000") and hemispherical images ("HI") for field based estimates of LAI(e). ALS penetration rate calculated from first echoes and from first and last echoes was strongly related to field estimates of LAI(e). We fitted regression models of LAI(e) against the log-transformed inverse of the ALS penetration rate, and in accordance with the Beer-Lambert law this produced a linear, no-intercept relationship. This was particularly the case for the LAI-2000, having R-2 values > 0.9. The strongest relationship was obtained by selecting ALS data from within a circle around each plot with a radius of 0.75 times the tree height. We found a slight difference in the relationship for the two years, which can be attributed to the differences in the ALS acquisition settings. The relationship was valid across four age classes of trees representing different stages of stand development, except in one case with newly regenerated stands which most likely was an artifact. Using LAI(e) based on HI data produced weaker relationships with the ALS data. This was the case even when we simulated LAI-2000 measurements based on the HI data. (C) 2009 Elsevier Inc. All rights reserved.
Sammendrag
In trees adapted to cold climates, conditions during autumn and winter may influence the subsequent timing of bud burst and hence tree survival during early spring frosts. We tested the effects of two temperatures during, dormancy induction Mid mild spells (MS) during chilling, on the timing of bud burst in three Picea abies (L.) Karst. provenances (58-66 degrees N). One-year-old seedlings were induced to become dormant at temperatures of 12 or 21 degrees C applied during 9 weeks of short days (12-h photoperiod). The seedlings were then moved to cold storage and given either continuous chilling at 0.7 degrees C (control), or chilling interrupted by one 14-day MS it either 8 or 12 degrees C. Interruptions with MS were staggered throughout the 175-day chilling period, resulting in 10 MS differing in date of onset. Subsets of seedlings were moved to forcing conditions (12-h photoperiod, 12 degrees C) throughout the chilling period, to assess dormancy status different timings of the MS treatment. Finally, after 175 days of chilling, timing of bud burst was assessed in a 24-h photoperiod at 12 degrees C (control and MS-treated seedlings). The MS treatment did not significantly affect days to bud burst when given early (after 7-35 chilling days). When MS was given after 49 chilling days or later, the seedlings burst bud earlier than the controls, and the difference increased with increasing length of the chilling period given before the MS. The 12 degrees C MS treatment was more effective than the 8 degrees C MS treatment, and the difference remained constant after the seedlings had received 66 or more chilling days before the MS treatment was applied. In all provenances, a constant temperature of 21 degrees C during dormancy induction resulted in more dormant seedlings (delayed bud burst) than a constant temperature of 12 degrees C, but this did not delay the response to the MS treatment.
Sammendrag
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2008
Sammendrag
Over the last decades the forestry sciences have been opened for new topics and methods. In addition to traditional forestry topics they have participated in environmental and ecosystem research. So far this type of research has been perceived as “applied”. From the modelling perspective there has been a misunderstanding among the participating disciplines of the character of knowledge being applied. Here we introduce two types of models of forest utilization and discuss their possibilities and limits for forestry sciences. The first perspective of forests is the one dominating in modelling today and in forestry sciences. It has been adopted from physics. The second perspective of forests has implicitly been adopted in the past for pragmatic reasons.
Sammendrag
Runoff time series are known to contain long term structures on interannual to decadal time scales. Investigating spatial patterns of long term structures is a way to elucidate the relationship between external forcings and watershed properties. This would be a valuable contribution to an improved water resources management. Singular System Analysis (SSA) is a powerful technique to identify and extract significant long term components from time series. However, many observations from natural systems are prone to missing data that hamper many analysis techniques, including the SSA in its original formulation...
Sammendrag
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 or periodic phenomena or nonlinear dynamics. Unfortunately, most of 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...
Sammendrag
Life on earth depends on water and where running water occurs on earth, there is life. Nevertheless, existing modelling approaches in hydrology almost completely neglect the biological aspects of water flow. We claim that ignoring biological behaviour and interaction in catchment runoff modelling is too restrictive, and that computational theories can be used to formalise behaviour and interaction and model the biological impact on runoff. To demonstrate this, starting with a general classification of catchment behaviour, as documented in runoff data, we will use symbolic dynamics to quantify randomness and complexity in the time series. This approach shows that runoff records from very different catchments show common behaviour. This behaviour can be fitted to a one-parametric curve, stratified into three regions. In this manner, it becomes possible to represent and classify types of interactive behaviour that cannot be generated algorithmically. This suggests that physically based catchment models do not properly represent all types of interactive behaviour, and that signatures of biological interaction are present in runoff data.