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.
1999
Forfattere
Svein SolbergSammendrag
Relationships within stands between growth and crown condition are presented. The data set contained about 25000 trees on 500 plots. Growth of single trees was determined by diameter measurements in 1991 and 1996. Diameter increments were recalculated to relative values in two steps; firstly relative to their stem diameter, and secondly relative to reference values for trees in the same plot, having no defoliation or no discoloration. These relative increment values, or growth indices, were distributed on a scale common for all plots, rendering them influenced neither by site and stand properties, nor by social status of each tree. The correlation between crown condition and growth, although of moderate strength, did validate crown condition assessments as a meaningful, but rough measure of forest health or vigour. The relationships were concave, and considerable growth depressions were already found at slight levels of defoliation and discoloration. Growth approached zero as defoliation and discoloration increased towards 100%. These relationships applied for all plots, regardless of their site productivity, development stage or regeneration method
Sammendrag
This study describes how crown density changes were distributed within monitoring plots, in order to determine whether the reduced crown density observed could be explained as a worsening of a limited number of unhealthy or small and slightly suppressed trees.Crown density, yellowing, coning and stem diameter data were available from 447 selected plots comprising 22560 single trees all having a complete 1990-97 series of crown condition data.The eight years series of crown density for each tree were recalculated to two median values, for 1990-93 and 1994-97, in order to reduce the influence from short time variations including random errors. The scores for yellowing and amounts of cones were averaged over the years 1990-93. These variables, and diameter, were recalculated to rank indices within each plot.Relationships between variables were described by graphs and examined by correlation analyses of the indices. The trees tended to retain their internal ranking. Generally, when crown density for a plot has changed, most of the trees were affected. The most defoliated trees in each plots had the least negative changes, but except from that the trees were equally affected regardless of their yellowing, amount of cones, and their size.The results demonstrates that any effects from competition between the trees were sufficiently removed in the assessments, even in densely stocked stands.
Sammendrag
This study aims to evaluate the quality of crown density data, based on independent, pairwise tree assessments. The data originates from monitoring of forest health (crown condition) in Norway; 250 plots, comprising 12 000 individual trees of Norway spruc e, have been reassessed by a single observer during 1990-95. Of the trees, 2300 were controlled more than twice, providing the possibility of evaluating the quality of assessed temporal changes of crown density. True errors (standard deviation) are estima ted to be about 10% for single trees and 5% for plot means, while the real standard deviation of the differences were slightly higher. The errors of the temporal changes of crown density were of similar magnitude. Systematic differences in crown density w ere found between sites and plot types, partly resulting from observer bias. However, the results suggest that observer bias is really the result of each observer\"s personal style in assessment.
Forfattere
Svein SolbergSammendrag
On the local county monitoring plots located throughout Norway a reduction of crown density has been noted during 1988-97. The aim of this study was to determine whether this change could be attributed to normal effects from increased age on the plots.The dataset comprised around 580 plots and 27 000 single trees of Norway spruce, where each tree was provided with ten years of crown density measures. A two step approach was used, firstly to search for an expectancy for normal reduction of crown density by age derived from the dataset, and then to compare this with the actual reduction. The interpretation was somewhat complicated as the various results were tangled into each other.Highly significant correlations were found between crown density and age. The relationship indicated an annual reduction of crown density around 0.12%-units, however, the relationship varied both between years and between regions, and it was not possible to definitely determine whether the relationship was best described by linear or non-linear models.Of major importance here is that the relationship appeared to be influenced by the presence of stresses, which effects tended to be more severe in old stands. Based on this it seems questionable whether an expectancy for normal ageing can be properly defined. However, in the present study it could still be definitely determined that the mean crown density change of -0.41%-units annually was too negative to be attributed to normal ageing, as it was clearly below all the suggested expectancies from the various models.This suggests that the amount of stress in the period under study has been higher than normal, and this encourages the search for causal agents in further studies. Changes in silviculture may have had some influence.The results were valid for most of Norway, with the exception of western and northern regions. Crown density assessments are subjective, which may possibly give erroneous time trends, however, it is argued that this is less likely to be of major importance in the present data.
Sammendrag
Det er ikke registrert sammendrag
Forfattere
Isabella BørjaSammendrag
Practical handbook for identification of diseases and disorders in european forest nurseries. Many colour photos and illustrations.
Forfattere
Anne Kari Bergjord Olsen Ada Engødegård Arne Hermansen Helge Sjursen Bonsak Hammeraas Christer Magnusson Leif SundheimSammendrag
Damping av jord er en gammel metode for bekjempelse av ugras, sopp, nematoder og virus. Desinfeksjon ved hjelp av damp ble tatt i bruk allerede i begynnelsen av forrige århundre, men det var først i begynnelsen av dette århundre metoden ble benyttet i større omfang, og da spesielt i veksthus. I motsetning til de kjemiske desinfeksjonsmidlene, hadde damping en mer universell virkning ved sin effekt både på ugrasfrø, nematoder, sopp og virus. Damping ble derfor av mange sett på som den beste metoden for desinfeksjon av jord (Newhall et al., 1931, og Baker, 1950). Etter hvert overtok imidlertid de kjemiske midlene markedet, og utviklingen av dampingsteknikken stoppet opp. Det er derfor relativt lite nyere litteratur og forsøksresultater fra bruk av jorddamping
Sammendrag
Det er ikke registrert sammendrag
Forfattere
Trond Henriksen T.A BrelandSammendrag
On twelve occasions during a two-year field experiment, we determined the decomposition of barley straw, ryegrass foliage, white clover foliage, potato haulm and white cabbage leaves confined in buried mesh bags that were protected against leaching. After one year, 49, 18, 8, 25 and 5 % of initial carbon (C) in the five crop residues remained, respectively. The corresponding figures for nitrogen (N) were 105, 32, 8, 36 and 11 %. The data were used to evaluate a simulation model developed during previous studies of crop residue C and N turnover under controlled temperature and moisture conditions. Description of plant residue degradability and model parameter values were taken from these studies. Rate-modifying functions were then added to take account of effects of measured soil temperature and moisture. The model gave a good overall description of crop residue degradation but slightly underestimated C release and, to a greater extent, N release during the first autumn and winter. The relatively rapid N loss in this period, suggested that low temperatures restricted microbial N immobilization more than it did gross decomposition. We hypothesized that this was caused by a reduced microbial growth yield efficiency (E) at low temperatures. When we reduced the value of E from 0.5 (default value) to 0.2 at 2 °C and below, model fit to C and N mineralization was improved substantially. Moreover, the model produced an excellent fit to remaining wheat straw C and a gave good description of N mineralization in an independent experiment, indicating that reducing the value of E was justified. The results suggested that crop residue degradability and the decomposer community were reasonably described in the model, that the rate-modifying functions of temperature, moisture and N availability were sound and that parameter values set under controlled conditions represented field conditions also, possibly except that of E.
Forfattere
Per Kraft Roger Roseth Harald BjørnstadSammendrag
Det er ikke registrert sammendrag