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361.
Portable chainsaws are associated with substantial risk and can cause serious injury to operators, especially during kickback. This paper presents new results from research and analyses conducted regarding the impact between the different properties of wood on this occurrence. In an open area, such differences may include: wood species, humidity, temperature and the facing angle of the wood fibres in relation to the kerf and shape of the wood surface that comes in contact with the tip of the guide bar. This paper investigates chainsaw kickback including the research results on kickback and wood-cutting energy, saw chain speed and the efficiency of the chainsaw engine. It also presents conclusions drawn from the tests that can be useful for chainsaw users, showing the dependencies between the different properties of wood and the risk of injury. 相似文献
362.
This paper analyses the political process for handling an outbreak of an insect causing human allergic reactions. In the southern part of the Swedish island Gotland in the Baltic Sea, an outbreak of the northern pine processionary moth, Thaumetopoea pinivora, has occurred. With regard to the human nuisance and long-term effects on the tourist industry, demands have been raised for intervention to reduce and control the insect population. At the same time, there have been warnings against treating the insect population because there are knowledge gaps concerning the wider ecological consequences, including effects on biodiversity. This paper analyses the political process and its problem-solving efforts. Of particular interest is how it dealt with the issue of uncertainty. It was found that the uncertainty associated with the issue hindered the development of a shared understanding of the problem and a possible solution. There seems to be a growing need in society to develop the institutional capacity to handle complex issues that cross different sectors, regulatory frameworks and policy targets. 相似文献
363.
Currently, China's timber industry is in high demand with the development of real estate. However, there is a certain fire hazard in the production process of wood manufacturing. Once a fire occurs, the fire is violent and the spread is rapid. Therefore, to improve the safety of its production process, ammonium dihydrogen phosphate and magnesium hydroxide were selected to prepare a new composite superfine dry powder, which was denoted as the NH4H2PO4/Mg(OH)2 composite. Furthermore, to figure out dry powders' extinction effect on Class A fire, the wood-crib fire suppression effect of the NH4H2PO4/Mg(OH)2 composite was test, and then compared with that of ultrafine dry powder (UDP) and commercial ABC dry powder (C-ABC) in a 1 m³ chamber. Three parameters of the fire extinguishing process, namely flame extinction time, powder consumption and temperature drop were adopted to measure the fire suppression performance. The results demonstrated that UDP and C-ABC both had a larger flame extinction time and powder consumption than the NH4H2PO4/Mg(OH)2 composite. Besides, a fire (wood cribs) can be extinguished by the NH4H2PO4/Mg(OH)2 composite with the fastest temperature drop and a much-improved toxic gas suppression ability. In short, the NH4H2PO4/Mg(OH)2 composite can better guarantee the safety of the wood processing production process. Moreover, the reasons for performance advantages of the NH4H2PO4/Mg(OH)2 composite were discussed. 相似文献
364.
A comparative analysis of field observations and experiments on the distance and rate of dispersal of self-sown Scotch pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) progeny has shown that the rate of their hydrochorous dissemination downstream is an order of magnitude higher than the rate of dispersal in upland areas. A hypothesis assigning priority to the role of hydrochory in the expansion of conifer populations to the tundra (periglacial) zone along with climate warming has been formulated and substantiated by comparative isozyme analysis of populations in transects lying along and across rivers. 相似文献
365.
Posttreatment Tree Mortality After Forest Ecological Restoration,Arizona, United States 总被引:1,自引:0,他引:1
Pine–oak forests are of high ecological importance worldwide, but many are threatened by uncharacteristically severe wildfire.
Forest restoration treatments, including the reintroduction of a surface fire regime, are intended to decrease fire hazard
and emulate historic ecosystem structure and function. Restoration has recently received much management attention and short-term
study, but little is known about longer-term ecosystem responses. We remeasured a replicated experimental restoration site
in the southwestern United States 5 years after treatments. Basal area, tree density, and canopy cover decreased in the treated
units at a faster rate than in controls. Delayed mortality, not evident right after treatment, decreased density modestly
(13% in treated units and 10% in controls) but disproportionately affected large trees (“large” ponderosa pines were those
with diameter at breast height [dbh] ≥37.5 cm; other species dbh ≥20 cm). In treated units, 10.9 large trees ha–1 died, whereas 6.2 trees ha–1 died in control units. Compared with reference conditions, the experimental blocks remained higher in pine density and, in
three of the four blocks, in basal area. Pine trees grew significantly faster in treated units than in controls, enough to
reach the reference level of basal area in 6 years. Although mortality of large trees is a concern, the treated units have
vigorous growth and low density, indicating that they will be relatively resistant to future drought and fire events. Similar
treatments may be beneficial in many areas of the United States and in related pine-oak ecosystems elsewhere. 相似文献
366.
Waste wood recovery by thermal treatment with energy recovery or by recycling allows the substitution and conservation of primary resources. Swiss government notes the potential presence of tensions between policies which simultaneously encourage the cascade use of wood, the recycling or the energy recovery by thermal treatment of waste wood. The aim of the present research is to assess the coherence of waste wood management in Switzerland by a quantitative and qualitative approach. First, a material flow analysis allows to model the wood resources and waste wood metabolism over one century. The simulation results of various scenarios of waste wood management establish that the additional impacts of the immediate thermal treatment are less significant for the reduction of CO2eq emissions but more significant for the energy production than its cascade treatments on Swiss territory. Secondly, a documentary analysis examines the determinants of the current waste wood treatments prevailing in Switzerland. Thus, the causes of the strong presence on Swiss territory of the sector of thermal treatment, the export of almost half of waste wood generated and the sub-exploitation of Swiss forest act as barriers or drivers that result in introducing a crowding-out effect where no amount of waste wood is available for recycling in Switzerland. The comparison of the results of the two approaches leads to the conclusion that the current waste wood management is coherent in relation to the various goals of the Swiss federal policies but the waste wood potential for energy production is not fully exploited. The recommendations on the waste wood management and the possibilities to use the model for other case studies are given in the conclusion. 相似文献