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Thirteen streams in the province of Jämtland in northern Sweden were monitored during spring in 1995 (December 94 – July 95) to study changes in water chemistry and metal concentrations during snow melt. The brooks are not treated with lime, with one exception, and can be approximately divided into three groups according to watershed characteristics; A) > 65% above tree line, B) > 65 % wetland, C) > 55% forested. During peak flow, pH dropped 0.5–2.5 units and alkalinity generally to zero. The brooks above tree line were lowest in base cations and reached the lowest pH-values (4.4–4.6) during peak flow, while sulphate levels were about the same as in the forested watersheds. During peak flow, organic anions showed the highest increase in the wetland and forested catchments. Compared to base flow, Al, Zn, Pb and to some extent Mn was enriched during peak flow. The results also illustrate the difficulties in generalising the reasons for alkalinity losses during spring flood in this kind of streams. In some of the brooks, the use of either base cations or silica, when calculating dilution effects, gave deviating results concerning the relative contribution of strong acids in the snow pack. 相似文献
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The main objective of this study was to examine the cost, flexibility, and appropriate scale of mechanized microsite preparation (MP), in combination with mechanical direct seeding of Pinus sylvestris L. with orchard seed. This technique was tested at four boreal forest sites in Northern Sweden. Orchard and stand seeds were sown with and without MP. The use of orchard seed increased seedling establishment by 41% and the use of MP increased seedling establishment by 47%, respectively, after two years. The best substrates for sowing when using MP were OAh-, E- and BC-horizon, in ranked order. The use of orchard seed compared to stand seed increased mean seedling height by 25% after four years. These trials suggest that to obtain a density of 5,000 stems ha-1 four years after seeding, 61,000 viable stand seeds or 41,000 orchard seeds ha-1 should be sown if MP is not used. If MP is used, seeding rate could be reduced by about 32%. By using MP, and by further improving scarification technique so that all scarified area is thin OAh-horizon, we predict that only 32,000 stand seeds or 22,000 orchard seeds ha-1, i.e., half the dosage, should be needed. Under these optimal conditions, it would be necessary to sow about six and four germinable stand and orchard seeds, respectively, to ensure one seedling after four years. Furthermore, regeneration cost would be less than a third that of planting. 相似文献
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Hooshang Majdi Laimi Truus Ulf Johansson Jan-Erik Nylund Håkan Wallander 《Forest Ecology and Management》2008
In the study reported here we examined the short-term effects (1–3 years) of slash retention (SR) and the long-term effects (13–15 years) of wood-ash application (A) on fine roots and mycorrhizae in a 40-year-old Norway spruce forest in southwest Sweden. Soil cores were used to obtain estimates of the biomass (g m−2) of roots in three diameter classes (<0.5, 0.5–1 and 1–2 mm), root length density (RLD), specific root length (SRL) and mycorrhizal root tip density (RTD). Fine root (<1 mm) length production and mortality, and mycelium production, were estimated using minirhizotron and mesh bag techniques, respectively. Compared with the control plots (C), the biomass of fine roots in diameter classes <0.5 mm and 0.5–1 mm was significantly higher in A plots, but lower in SR plots. In addition, RLD was significantly lower in the humus layer of SR plots than in the humus layers of C and A plots, but not in the other layers. None of the treatments affected the SRL. In all soil layers, the SR treatment resulted in significant reductions in the number of ectomycorrhizal root tips, and the mycelia production of fungi in mesh bags, relative to the C treatment, but the C and A treatments induced no significant changes in these variables. Fine root length production in the C, A and SR plots amounted to 94, 87 and 70 mm tube−1 during the 2003 growing season, respectively. Fine root mortality in treated plots did not change over the course of the study. We suggest that leaving logging residues on fertile sites may result in nitrogen mineralisation, which may in turn induce reductions in root biomass, and both root and mycelium production, and consequently affect nutrient uptake and the accumulation of organic carbon in soil derived from roots and mycorrhizae. 相似文献
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Jan-Erik Berg 《Wood Science and Technology》2001,35(4):343-351
The fiber separation step in refining is crucial for energy consumption in subsequent refining where the pulp properties
are developed. The size reduction of chips during refining is dependent on refining intensity and chip strength. Factors affecting
these two parameters are discussed in a literature review. The impact strength of chips and the break down of chips to separate
fibers are also discussed. Specifically the effect of impact velocity on the fracture of wood has been studied by use of a
falling weight impact tester. Samples were prepared from a freshly cut log of Norway spruce, Picea abies, and the impact strength was measured using an instrumented falling weight impact tester. An increase in impact velocity
from about 2.7 to 4.8 m/s resulted in an increase in impact strength of about 50%.
Received 23 August 1999 相似文献
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The large-scale pulp investment model, with its pressure on land, has created conflict and caused major disagreements and open hostility amongst the social movement and NGO networks, state actors, and the pulp and paper companies in Brazil. In this article, Ethical Analysis was applied in the assessment of the dynamics and possibilities of conflict resolution related to the expansion of pulpwood plantations in Brazil's Bahia State, particularly near Veracel Celulose. Ethical Analysis as a tool identifies the complex dynamics of contention through identifying bridges and rifts in the social, ecological and economic viewpoints of the main actors. The analysis was based on field research, interviews, and a review of existing literature. The results indicated that the conflict is marked by politics of power, and as long as this stage continues, the politics of cooperation and conflict resolution would be hard to achieve. The key actors have diverging interests, values and principles, and different ways of presenting their viewpoints. The current investment context is economically and institutionally peripheral and socially weak. Without a radical rethinking and emphasis on ethical and structural reworking of the investment model, the conflict will likely continue to deepen, aggravating investment risk for large-scale business and industrial forestry. 相似文献
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