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.
2017
Forfattere
Hans Petersson Johannes Breidenbach David Ellison Sören Holm Anders Muszta Mattias Lundblad Göran R. StåhlSammendrag
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Sammendrag
Estimates of stand averages are needed by forest management for planning purposes. In forest enterprise inventories supported by remotely sensed auxiliary data, these estimates are typically derived exclusively from a model that does not consider stand effects in the study variable. Variance estimators for these means may seriously underestimate uncertainty, and confidence intervals may be too narrow when a model used for computing a stand mean omits a nontrivial stand effect in one or more of the model parameters, a nontrivial spatial distance dependent autocorrelation in the model residuals, or both. In simulated sampling from 36 populations with stands of different sizes and differing with respect to (i) the correlation between a study variable (Y) and two auxiliary variables (X), (ii) the magnitude of stand effects in the intercept of a linear population model linking X to Y, and (iii) a first-order autoregression in Y and X, we learned that none of the tested designs provided reliable estimates of the within-stand autocorrelation among model residuals. More-reliable estimates were possible from stand-wide predictions of Y. The anticipated bias in an estimated autoregression parameter had a modest influence on estimates of variance and coverage of nominal 95% confidence intervals for a synthetic stand mean.
Sammendrag
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Sammendrag
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Forfattere
Milan Lstibůrek Yousri A. El-Kassaby Tore Skrøppa Gary R. Hodge Jørn Henrik Sønstebø Arne SteffenremSammendrag
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Sammendrag
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Sammendrag
The use of digital aerial photogrammetry (DAP) for forest inventory purposes has been widely studied and can produce comparable accuracy compared with airborne laser scanning (ALS) in small, homogeneous areas. However, the accuracy of DAP for large scale applications with heterogeneous terrain and forest vegetation has not yet been reported. In this study we examined the accuracy of timber volume, biomass and basal area prediction models based on DAP and national forest inventory (NFI) data on a large area in central Norway. Two separate point clouds were derived from aerial image acquisitions of 2010 and 2013. Vegetation heights were extracted by subtracting terrain elevation derived from ALS. A large number of NFI sample plots (483) measured between 2010 and 2014 were used as reference data to fit linear models for timber volume, biomass and basal area with height metrics derived from the DAP data as explanatory variables. Variables describing the heterogeneous environmental and image acquisition conditions were calculated and their influence on the model accuracy was tested. The results showed that forest parameter prediction using DAP works well when applied to a large area. The model fits of the timber volume, biomass and basal area models were good with R2 of 0.80, 0.81, 0.81 and RMSEs of 41.43 m3 ha−1 (55% of the mean observed value), 32.49 t ha−1 (47%), 5.19 m2 ha−1 (41%), respectively. Only a small proportion of the variation could be attributed to the heterogeneous conditions. The inclusion of the relative sun inclination led to an improvement of the model RMSEs by 2% of the mean observed values. The relatively low cost and stability across large areas make DAP an attractive source of auxiliary information for large scale forest inventories.
Forfattere
Belachew Gizachew Zeleke Rasmus Astrup Pål Olav Vedeld Eliakimu M. Zahabu Lalisa A. DugumaSammendrag
REDD+, a climate change mitigation mechanism that values carbon in tropical forests, is expected to provide Africa with a range of environmental and socio-economic benefits. Drawing on a vast array of literature and personal experiences, this review analyzed particular features and challenges that REDD+ implementation has faced on the continent. The distinct contexts and major challenges regarding governance, finance and technical capacities are discussed, and mechanisms to fill these gaps are suggested. Radical land tenure reform and a perfect safeguard mechanism that transfers forest land and carbon to the communities are unlikely. REDD+ should rather look for systems that respect local institutional arrangements, and allow forest-based communities to participate in decision-making and benefit sharing, particularly benefits from emerging REDD+. Finances for REDD+ infrastructure and the results-based payment are in short supply. While negotiating for potential external sources in the short term, Africa should generate domestic financial resources and look for additional payments for ecosystem services. Africa should also negotiate for forest monitoring capacity building, while strengthening local community forest monitoring. This review contributes to an improved understanding of the contexts and challenges to consider in the capacity and policy development for REDD+ implementation.
Forfattere
Graham Alan Ormondroyd Gry Alfredsen Raghavalu Thirumalai Durai Prabhakaran Simon F. Curling Bronia K. Stefanowski Morwenna J. Spear Lone RossSammendrag
Microbiological degradation of wood by decay fungi can cause a rapid change in the structural properties of timber which can result in both strength and mass loss. Traditional techniques for the evaluation of decay (e.g. mass loss) lack the sensitivity to evaluate the effects of the very first stages of the decay process. This paper describes the effects of initial brown rot decay, defined by the amount of Poria placenta genomic DNA (gDNA) present in the samples, on the dynamic mechanical properties of the timber. It was found that there is a correlation between the mean storage modulus of the timber and the amount of P. placenta gDNA present, and therefore the level of decay. This shows that using dynamic mechanical analysis is a viable technique that can be used to study initial decay processes.
Sammendrag
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