排序方式: 共有19条查询结果,搜索用时 15 毫秒
1.
Dr. Oskar Bernbeck 《European Journal of Forest Research》1911,33(4):210-211
2.
Dead wood is a critical resource for biodiversity in boreal forests. We analysed the persistence of five model species inhabiting
dead wood. By parameterising a metapopulation model (the incidence function model), the model species were all assigned characteristics
that makes it likely that they have disappeared from some (20%) forest landscapes with a long history of forest management.
In the metapopulation model, a forest stand (5 ha) was regarded as a habitat patch. The amount of habitat in each patch was
obtained from models of dead wood dynamics of Norway spruce in central Sweden. Dead wood generated by altered management over
the entire landscape was found to be less efficient in reducing extinction risks in comparison to the same amount of dead
wood generated by protecting reserves. Because generation of dead wood by altered management is often less expensive than
setting aside reserves, it is difficult to determine which conservation measure is most cost-efficient. In a landscape subjected
to forestry for the first time, it was better to preserve a few large reserves than many small ones. However, in a managed,
highly fragmented forest landscape it was better to set aside many small reserves. The reason for this was that small plots
with high habitat quality could be selected, while large reserves originally contained habitats both of high and low quality,
and the rate of habitat quality increase was low. A strategy for biodiversity conservation in a managed forest landscape should
include information about the history of the landscape, the current amount and spatial distribution of forest habitats, and
the potential for rapid restoration of forest habitats, both on managed and unmanaged forest land. 相似文献
3.
Franklin O Johansson J Dewar RC Dieckmann U McMurtrie RE Brännström A Dybzinski R 《Tree physiology》2012,32(6):648-666
We review approaches to predicting carbon and nitrogen allocation in forest models in terms of their underlying assumptions and their resulting strengths and limitations. Empirical and allometric methods are easily developed and computationally efficient, but lack the power of evolution-based approaches to explain and predict multifaceted effects of environmental variability and climate change. In evolution-based methods, allocation is usually determined by maximization of a fitness proxy, either in a fixed environment, which we call optimal response (OR) models, or including the feedback of an individual's strategy on its environment (game-theoretical optimization, GTO). Optimal response models can predict allocation in single trees and stands when there is significant competition only for one resource. Game-theoretical optimization can be used to account for additional dimensions of competition, e.g., when strong root competition boosts root allocation at the expense of wood production. However, we demonstrate that an OR model predicts similar allocation to a GTO model under the root-competitive conditions reported in free-air carbon dioxide enrichment (FACE) experiments. The most evolutionarily realistic approach is adaptive dynamics (AD) where the allocation strategy arises from eco-evolutionary dynamics of populations instead of a fitness proxy. We also discuss emerging entropy-based approaches that offer an alternative thermodynamic perspective on allocation, in which fitness proxies are replaced by entropy or entropy production. To help develop allocation models further, the value of wide-ranging datasets, such as FLUXNET, could be greatly enhanced by ancillary measurements of driving variables, such as water and soil nitrogen availability. 相似文献
4.
5.
To investigate the linkage types between carbohydrates and lignin, residual lignins were isolated from three different unbleached
pulps [kraft, alkaline sulfite anthraquinone methanol (ASAM), and soda with anthraquinone (AQ) and methanol] of spruce and
beech wood and then characterized by oxidation with 2,3-Dichloro-5,6-dicyanobenzoquinone and followed by Prehm’s methylation.
In residual lignins, sugar moieties were bound to lignins via benzyl ether bonds. In particular, galactose and mannose are
predominantly linked to lignin fragments in residual lignins of spruce wood, while xylose and galactose are favored in the
formation of LC bonds in the residual lignins of beech wood. In the case of hexoses, primary hydroxyl groups (C6 position)
preferentially take part in benzyl ether linkages. Hydroxyl groups in the C2 and C3 positions of xylose participate in LC
bonds and a small portion of arabinose was notably connected to lignin via the C5 position. Approximately seven or eight sugars
were connected in soda/AQ/methanol residual lignin per 100 C9 lignin units, while the frequencies of LC bonds in kraft and
ASAM residual lignins were distinctively less at one to three sugars per 100 C9 lignin units.
The publication of this article was made possible by an Emachu Research Fund. The authors are grateful for the fund. 相似文献
6.
In growing cities, there is a demand for development areas, which poses a threat to existing green areas. Therefore, it is of interest to know to what extent different types of green areas are used by residents. In the suburb of Järvafältet, situated 15 km outside Stockholm city centre, inhabitants’ use of patches of remnants of original natural vegetation in green areas has been studied by momentary observations from fixed points over the periods 1978–1982 and 2002–2004. The number of people, sex, age, type of activity, and place of that activity were noted. Overall, there has been a significant increase in the amount of use of these types of recreation areas between the two periods. The use by organized groups, as well as by adult walkers, runners and cyclists, increased the most, while individual children's play decreased. Almost every other child observed was found to be partaking in organized school or day nursery group activities. Children belonging to organized groups were seen as frequently in areas at a distance of less than 100 m from the houses as between 200 and 400 m from the built-up area, while children not participating in group activities were seen much more frequently in the areas closest to buildings. These types of green areas were used more by children and young people than by adults. This implies the likelihood that the use of these areas for recreation is underestimated in outdoor recreation inquiries and interview studies, where children are not usually included. Residents’ use of areas with remnant natural vegetation in cities shows that these areas have a recreational value as well as with other values. This makes them important to take into consideration in the planning and design process. Small areas close to residential areas need to be considered. 相似文献
7.
Asvany O P PK Redlich B Hegemann I Schlemmer S Marx D 《Science (New York, N.Y.)》2005,309(5738):1219-1222
Protonated methane, CH5+, continues to elude definitive structural assignment, as large-amplitude vibrations and hydrogen scrambling challenge both theory and experiment. Here, the infrared spectrum of bare CH5+ is presented, as detected by reaction with carbon dioxide gas after resonant excitation by the free electron laser at the FELIX facility in the Netherlands. Comparison of the experimental spectrum at approximately 110 kelvin to finite-temperature infrared spectra, calculated by ab initio molecular dynamics, supports fluxionality of bare CH5+ under experimental conditions and provides a dynamical mechanism for exchange of hydrogens between CH3 tripod positions and the three-center bonded H2 moiety, which eventually leads to full hydrogen scrambling. The possibility of artificially freezing out scrambling and internal rotation in the simulations allowed assignment of the infrared spectrum despite this pronounced fluxionality. 相似文献
8.
Background
Vancomycin resistant enterococci (VRE) in Swedish broiler production has been shown to persist at farms between batches. The aim of this study was therefore to determine the possibility to eliminate VRE by disinfection of compartments in broiler houses as a proof of concept.Findings
VRE could not be detected in environmental samples from the disinfected test compartments in the broiler houses but was detected in environmental samples from the control compartments. The proportion of broilers colonized with VRE decreased in both the test and the control compartments.Conclusions
The results are promising and show that the occurrence of VRE in broiler houses can be reduced by adequate cleaning and disinfection with a combination of steam and formaldehyde. 相似文献9.
Zheng J Yang B Ruusunen V Laaksonen O Tahvonen R Hellsten J Kallio H 《Journal of agricultural and food chemistry》2012,60(26):6581-6593
Phenolic compounds in black currants of three Finnish cultivars and their response to growth latitude and weather conditions were analyzed over a six-year period. 'Melalahti' had lower contents of total phenolic compounds (31.4% and 29.2% lower than 'Mortti' and 'Ola', respectively), total anthocyanins (32.6% and 30.5%), and total hydroxycinnamic acid derivatives (23.1% and 23.8%) (p < 0.05) and was less affected by growth latitude and weather conditions than 'Mortti' and 'Ola'. However, all the cultivars grown at higher latitude (66°34' N) had lower contents of total flavonols, total anthocyanins, and total phenolic compounds than those grown at lower latitude (60°23' N) (p < 0.05). The content of total hydroxycinnamic acid conjugates did not vary in 'Melalahti' (p > 0.05) but increased as the latitude increased in 'Mortti' and 'Ola' (p < 0.05). Temperature and radiation were the major weather variables influencing the composition of phenolic compounds. Delphinidin-3-O-glucoside, delphinidin-3-O-rutinoside, and myricetin-3-O-glucoside content showed positive correlations with temperature and radiation in all three cultivars. The study gives important guidelines for the selection of raw materials and growth sites as well as for the berry cultivation for commercial exploitation of black currant berries. 相似文献
10.