Publications
NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.
2002
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Ole Martin Eklo Olav Lode Randi Bolli Reidun Aspmo Gunnhild Riise Tore Krogstad Brit Salbu Johannes DeelstraAbstract
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Tore SkrøppaAbstract
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Christel ElvestadAbstract
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Kjersti Holt HanssenAbstract
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Erik Næsset Tonje ØklandAbstract
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Erik Næsset Tonje ØklandAbstract
Tree height, the height from the ground surface to the tree crown, and the crown length as a proportion of tree height of individual trees were derived from various canopy height metrics measured by a small-footprint airborne laser scanner flown over a boreal forest reserve. The average spacing on the ground of the laser pulses ranged from 0.66 to 1.29 m. Ground-truth values were regressed against laser-derived canopy height metrics. The regressions explained 75%, 53%, and 51% of the variability in ground-truth tree height, height to the crown, and relative crown length, respectively. Cross-validation of the regressions revealed standard deviations of the differences between predicted and ground-truth values of 3.15 m (17.6%), 2.19 m (39.1%), and 10.48% (14.9% of ground-truth mean), respectively. On 10 plots with size 50 m2 in the boreal forest reserve and on 27 plots with size 200 m2 in a managed spruce forest, mean tree height, average height from the ground surface to the crown, and average relative crown length were regressed against laser canopy height metrics. The coefficients of determination (R2) ranged from .47 to .91. Cross-validation revealed a precision of 1.49 m (7.6%), 1.24-1.52 m (20.9-23.3%), and 6.32-7.11% (8.8-10.9% of ground-truth mean) for mean tree height, average height to the crown, and average relative crown length, respectively. At least, mean tree height can be determined more accurately from laser data than by current methods.
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Tor MykingAbstract
Additive variation in adaptive traits is a prerequisite for selection and adaptation to future environmental changes, but distribution of adaptive genetic variability between and within populations is poorly known in most forest trees. Owing to this deficiency, life history traits such as geographic range, pollination vector and seed dispersal capability, which significantly affect gene flow and thus the distribution of genetic variability, were used to evaluate the genetic resources in 23 Norwegian native forest tree species. Based on the combination of life history traits the species\" genetic resources were classified either as viable, potentially vulnerable or vulnerable, assuming a decrease in within-population variability in this sequence. Twelve widely distributed species with generally effective dispersal of pollen and seeds were considered viable (Pinus sylvestris, Picea abies, Juniperus communis, Betula pubescens, B. pendula, Alnus incana, A. glutinosa, Salix caprea, Populus tremula, Corylus avellana, Sorbus aucuparia, Prunus padus) and have as such no particular conservation needs. Effective seed dispersal of these species, as inferred from post-glacial migration rates, may be partly responsible for their generally early post-glacial appearance, and may, in combination with the wide ranges and relatively large evolutionary potential, indicate that viable species are best able to cope with climatic change. Among species with restricted ranges and more limited gene flow eight were considered potentially vulnerable (Quercus petraea, Q. robur, Fraxinus excelsior, Acer platanoides, Taxus baccata, Ilex aquifolium, Fagus sylvatica, Ulmus glabra) and three were considered vulnerable (Tilia cordata, Malus sylvestris, P. avium). Application of different intensities of a multiple population breeding system (MPBS) is considered the most appropriate mode of conserving genetic resources in these species.