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
Abstract
Foliage nutrient concentrations of overstorey and understorey Norway spruce (Picea abies (L.) Karst.), and height growth and needle weights of understorey saplings, were studied in a seven-year period after harvest. The following treatments were applied on each of three sites five years prior to needle sampling: control with no cutting, partial cutting with 50-60 % removal of basal area, and patch cut (25 x 25 m - 0.063 ha clear-cut). Saplings on control plots had higher concentrations of K and Cu in current-year needles (C) than overstorey trees. Increased harvest intensity led to a reduction of K in C- needles and Mg in (C+1)-needles of saplings, and of B in both saplings (C, C+1) and overstorey trees (C+1). Sapling needle weights generally increased with harvest intensity, whereas no effect of foliage N status on needle weights could be detected. The growth response of saplings was explained by the interaction between foliage N status, quantified as average N concentration in C- and (C+1)-needles, and harvest intensity. The results illustrate that sufficient N supply is a key factor for the ability of advance regeneration to utilize the improved light condition associated with overstorey removal.
Abstract
Injuries and mortality to advance growth (saplings) after selection harvesting was studied in 17 multi-storied Norway spruce (Picea abies (L.) Karst.) stands. Harvest removals ranged from 33 to 67 % of initial basal area. Four of the stands were harvested motor-manually (chain saw + skidding with farm tractors; M-FT). The remaining stands were harvested with single-grip harvesters and forwarders (H-FW). In each stand, injury rates were evaluated on a 24x48 m plot, located between the centrelines of two parallel striproads that were spaced 24 m apart. All logging teams had at least five years of experience in clear-cutting and thinning operations. The trees to be removed, and striproad centrelines, were marked prior to harvest. Mortality varied between 5 and 51 %, whereas total injury (injured + dead saplings) varied between 17 and 76 %. Mortality- and injury levels were generally highest on H-FW plots. Crown reduction and leaning stems were the most frequent types of injury, regardless of operating method. Injury rates increased with sapling height with the H-FW method, whereas the opposite was found on M-FT plots. Saplings without pre-harvest damage in the form of top- or leader defects had a higher probability of being injured than saplings with such damage in stands harvested with the M-FT method. A similar difference was not found on H-FW plots. A logistic regression model show that the spatial risk for injury depends on the interaction between forest condition factors and operational characteristics. Forest condition factors influencing the risk of injury are sapling height and the location of saplings relative to larger residual trees and striproads. Corresponding operational characteristics are operating method and harvest intensity.
Authors
Anders Göransson Toril Drabløs EldhusetAbstract
The results strongly suggest that the growth rate of N. spruce is not correlated with the basecation/Al ratio in the rooting medium, but with the basecation/nitrate ratio
Authors
Tore SkrøppaAbstract
No abstract has been registered
Abstract
Two zone sites, i.e. two circular areas with 50 km radius, were established in southern Norway. The zone sites were centred in Tofte (the location of a major pulp mill) and in Drammen (the site of a major timber yard). From June to October 2000, 66 forest blocks were visited, 65 of which were situated within the zone site areas. Samples were collected from 40 forest blocks, especially from wood attacked by wood boring insects. At 34 forest blocks, trees of Scots pine, Pinus sylvestris, or Norway spruce Picea abies were provided as trap-logs for Monochamus spp. This material will be sampled in the survey of 2001. Some samples were also taken from a wood chip pile and from imported wood material. The total number of wood samples analysed for nematodes were 275. Out of these, 214 samples were collected from forest trees, stumps, timber and logging wastes of P. sylvestris and P. abies. Three samples contained nematodes belonging to the genus Bursaphelenchus, but the Pine Wood Nematode (PWN), B. xylophilus, was not detected. Similarly, this nematode was not detected in the 10 samples of wood chips, or in the 25 samples of imported lumber or in the 26 samples of imported solid wood packing material. In order reach the minimal number of 3000 samples within reasonable time, the number of samples for the next survey season of 2001 needs to be increased drastically. To achieve this, the sampling will continue within the existing zone sites, and be extended into new zone sites to be established in 2001.
Authors
Steen Koekebakker Gudbrand LienAbstract
Empirical evidence suggests that agricultural futures price movements have fat-tailed distributions and exhibit sudden and un xpected price jumps. There is also evidence that the volatility of futures prices contains a term structure depending on both calendar-time and time to maturity. This paper extends Bates (1991) jump-diffusion option pricing model by including both seas nal and maturity effects in volatility. An in-sample fit to market option prices on wheat futures show that our model outperforms previous models considered in the literature. A numerical example illustrates the economic significance of our results for option valuation.
Abstract
No abstract has been registered
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No abstract has been registered
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Authors
Svein Ole BorgenAbstract
No abstract has been registered