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.
2001
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Abstract
In 1996, 7000 ha of pine forests were defoliated by the pine looper Bupalus piniaria in south-western Sweden.The susceptibility of trees of different defoliation classes (0, 30, 60, 90 and 100% defoliation) to beetle-vectored blue-stain fungi was tested in inoculation experiments.Forty and 120-year-old Scots pine trees were inoculated with `single\", i.e. a few inoculations of Leptographium wingfieldii and Ophiostoma minus, two blue-stain fungi associated with the pine shoot beetle Tomicus piniperda. The young trees were also \"mass\" inoculated with L. wingfieldii at a density of 400 inoculation points per m2 over a 60 cm stem belt.Host tree symptoms indicated that only trees with 90100% defoliation were susceptible to the mass inoculation.Single inoculations did not result in any consistent differences in fungal performance between trees of different defoliation classes, regardless of inoculated species or tree age class.Leptographium wingfieldii produced larger reaction zones than O. minus, and both species produced larger lesions in old than in young trees.As beetle-induced tree mortality in the study area occurred only in totally defoliated stands, mass inoculations seem to mimic beetle-attacks fairly well, and thus seem to be a useful tool for assessing host resistance.As even severely defoliated pine trees were quite resistant, host defence reactions in Scots pine seem to be less dependent on carbon allocation than predicted by carbon-based defence hypotheses.
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Svein Ole BorgenAbstract
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Authors
Heleen A. de Wit Jan Mulder Per Holm Nygaard Dan Aamlid Magne Huse Egil Kortnes Gro Wollebæk Roald BreanAbstract
Aluminium (Al) is a key element in critical load calculations for forest. Here, we argue for re-evaluating the importance of Al. Effects of two levels of enhanced Al concentrations and lowered Ca:Al ratios in the soil solution in a field manipulation experiment in a mature spruce stand (1996-1999) on tree vitality parameters were tested. In addition, Al solubility controls were tested. Various loads of Al were added to forest plots by means of an irrigation system. Potentially toxic Al concentrations and critical ratios of Ca to inorganic Al were established.The ratio of Ca to total Al was not a suitable indicator for unfavourable conditions for plant growth. No significant effects on crown condition, tree growth and fine root production were observed after three years of treatment. In 1999, foliar Mg content in the highest Al addition treatment had declined significantly. This agreed with the known response to Al stress of seedlings in nutrient solution experiments. No support was found for using the chemical criterion Ca:Al ratio in soil solution, foliar and root tissue as an indicator for forest damage due to acidification. Al solubility was considerably lower than implied by the assumption of equilibrium with gibbsite, particularly in the root zone.The gibbsite equilibrium is commonly used in critical load models. Substitution of the gibbsite equilibrium with an Al-organic matter complexation model to describe Al solubility in soil water may have large consequences for calculation of critical loads. The results indicate that critical load maps for forests should be reconsidered.
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Jan Mulder Heleen A. de Wit Helena W.J. Boonen Lars R. BakkenAbstract
No abstract has been registered
Authors
Nina Syversen Brit SalbuAbstract
The purpose of the study is to use soil particles labeled with the radioactive tracer cesium-134 as a method for studying soil erosion and sedimentation pattern within a small catchment with buffer zones. Cesium is adsorbed to soil particles, and by mea suring changes in the Cs-134 activity on the soil surface, erosion, sedimentation, and pathways for particles can be traced.
Authors
Heleen A. de Wit Tore Groseth Jan MulderAbstract
No abstract has been registered