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.
1998
Abstract
No abstract has been registered
Authors
Bridget A. Emmett O. Janne Kjønaas Per Gundersen Chris J. Koopmans Albert Tietema D. SleepAbstract
Chronic atmospheric nitrogen deposition can alter the rate of internal nitrogen cycling and increase the magnitude of N leaching losses in forested ecosystems. As fractionation of nitrogen in favour of the lighter 14N occurs during various transformations associated with N-enrichment and nitrogen loss, it has been proposed that the 15N signal of vegetation may provide a useful tool in evaluating the past and current N status of forested ecosystems. A series of coniferous forests across a European nitrogen deposition gradient within the NITREX project provided an opportunity to test the relationships between nitrogen supply from atmospheric deposition and the relative 15N-enrichment of vegetation to soil, across a large geographical area. Most 15N values for above- and below-ground tree components, soil at four depths, bulk precipitation and/or throughfall water and soil solution or outflow water values were within those observed elsewhere except for a few notable exceptions.There was a significant positive relationship between the 15N enrichment of the tree foliage relative to the soil horizons (or the enrichment factor), and nitrogen flux in the throughfall if Aber forest, N. Wales, was excluded from the regression analysis. An unusually high enrichment factor at the Aber site indicated that a the high rate of N cycling at the site was in excess of that predicted from current N deposition. This was attributed to the effect of ploughing and tree planting on the relatively N- and clay-rich mineral horizons at Aber compared to other sites. Highly significant relationships (P 0.01) between enrichment factors and parameters describing internal rates of N cycling, such as litterfall N flux and nitrification rates in upper soil horizons, supported this conclusion. There appears to be a strong link between the rate of N cycling and the 15N enrichment factor, rather than N deposition or nitrate leaching per se. These results confirm the potential use of the 15N enrichment factor to identify sites influenced by nitrogen deposition. However, consideration should be taken of other site characteristics and land management practises which also influence soil N dynamics and N cycling.
Authors
Ketil KohmannAbstract
No abstract has been registered
Authors
Bridget A. Emmett D. Boxman M. Bredemeier Per Gundersen O. Janne Kjønaas Filip Moldan Patrick Schleppi Albert Tietema Richard Frederic WrightAbstract
No abstract has been registered
Authors
Halvor Solheim Harald KvaalenAbstract
No abstract has been registered
Abstract
No abstract has been registered
Authors
Sondre Skatter Olav Albert HøibøAbstract
Scots pine (Pinus silvestris) logs and 106 Norway spruce (Picea abies) logs. Two of the models were the classical 3-parametric circle model and the 5-parametric ellipse model. These models were compared to the third model, the Fourier coefficient model, which had a variable number of parameters. By increasing the number of parameters in the Fourier coefficient model, this model fits the true shape perfectly. With the same number of parameters the Fourier model performed approximately as good as the two other models. To get a substantial improvement over the ellipse model the number of parameters had to be raised dramatically.
Abstract
No abstract has been registered
Authors
M. Bendz-Hellgren Katriina Lipponen Halvor Solheim Iben Margarethe ThomsenAbstract
No abstract has been registered
Authors
Geir-Harald Strand Tonje Økland Rune Halvorsen ØklandAbstract
Change in crown density for Norway spruce (Picea abies (L.) Karst.) from 1988 to 1993 in three independent forest monitoring projects in southern Norway were compared. An increase in crown density was found in countrywide systematic random sample, while measurements taken in old-growth forests reported a decline. These contradictory results may be due to (1) high sensitivity of high-elevation forests to various kinds of environmental impact; (2) differences in stand-age and management practice; and (3) different densitivity to long distance airborne pollutants. The systematic random sample encompassed stand of several age classes from two counties, while the two other studies were restricted to old-growth forest in two smaller areas. A possible explanation of the differences is thus that the three studies refer to different populations as a result of different sampling strategies.