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Greenough Julee A. Apps Michael J. Kurz Werner A. 《Mitigation and Adaptation Strategies for Global Change》1997,2(2-3):267-283
The Intergovernmental Panel on Climate Change (IPCC) has developed guidelines to standardize the international reporting of greenhouse gas emissions and removals by signatory nations of the UN Framework Convention on Climate Change. With regard to forest sector carbon fluxes, the IPCC guidelines require only that those fluxes directly associated with human activities (i.e., harvesting and land-use change) be reported. In Canada, the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS2) has been used to assess carbon fluxes from the entire forest sector. This model accounts for carbon fluxes associated with both anthropogenic and natural disturbances, such as wild fires and insects. We combined model results for the period 1985 to 1989 with additional data to compile seven different national carbon flux inventories for the forest sector. These inventories incorporate different system components under a variety of seemingly plausible assumptions, some of which are encouraged refinements to the default flux inventory described in the IPCC guidelines. The resulting estimated net carbon fluxes varied from a net removal of 185,000 kt carbon per year of the inventory period to a netemission of 89,000 kt carbon per year. Following the default procedures in the IPCC guidelines, while using the best available national data, produced an inventory with a net removal of atmospheric carbon. Adding the effect of natural disturbances to that inventory reversed the sign of the net flux resulting in a substantial emission. Including the carbon fluxes associated with root biomass in the first inventory increased the magnitude of the estimated net removal. The variability of these results emphasizes the need for a systems approach in constructing a flux inventory. We argue that the choice of which fluxes to include in the inventory should be based on the importance of these fluxes to the overall carbon budget and not on the perceived ease with which flux estimates can be obtained. The results of this analysis also illustrate two specific points. Even those Canadian forests which are most free from direct human interactions—forests in which no commercial harvesting occurs—are not in equilibrium, and their contribution to national carbon fluxes should be included in the reported flux inventory. Moreover, those forest areas that are subject to direct management are still substantially impacted by natural disturbances. The critical effect of inventory methodology and assumptions on inventory results has important ramifications for efforts to “monitor” and “verify” programs aimed at mitigating global carbon emissions. 相似文献
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Kurz Werner A. Beukema Sarah J. Apps Michael J. 《Mitigation and Adaptation Strategies for Global Change》1997,2(4):405-421
Land-use change from an unmanaged to a managed forested landscape in northern forests is associated with a reduction of the
area annually affected by natural disturbances (wildfires and forest insects) and the introduction of harvesting as a new
disturbance. This study examined the impacts of changes in the disturbance regime-the frequency and type of disturbance-on
landscape-level carbon (C) content and fluxes. The Carbon Budget Model of the Canadian Forest Sector was used to assess these
impacts in six representative landscapes (100,000 ha each) with a range of disturbance regimes that are characteristic of
conditions in coastal British Columbia, the interior of British Columbia, and the eastern boreal forest in Canada. The model
was used to simulate ecosystem C fluxes during a period of natural disturbances, a 50-year transition period during which
harvesting replaced natural disturbances, followed by 150 years of harvesting. The initial landscape-level biomass C content
under natural disturbance regimes in the six example landscapes was 22 to 75% of their potential maximum content which is
often used as the reference or baseline case. After 200 years of forest management, the C stored in the landscape plus the
C retained in forest products manufactured from harvested biomass was between 58 and 101% of the landscape C content prior
to the onset of harvesting. Landscape-level ecosystem C content was found to be affected by changes in the disturbance frequency,
the age-dependence of the disturbance probabilities, and the disturbance-specific impacts on ecosystem C content. The results
indicate that using the potential maximum C content of a landscape as the baseline always overestimates the actual C release
due to land use change. A more meaningful procedure would be to assess the actual differences in landscape-level C content
between the natural and the managed disturbance regime. 相似文献
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Werner E. G. Müller 《Die Naturwissenschaften》1998,85(1):11-25
Geodia cydonium , which code for proteins. The analyses of their deduced amino acid sequences allowed a molecular biological approach to solve
the problem of monophyly of Metazoa. Molecules of the extracellular matrix/basal lamina, with the integrin receptor, fibronectin,
and galectin as prominent examples, cell-surface receptors (tyrosine kinase receptor), elements of sensory systems (crystallin,
metabotropic glutamate receptor), and homologs/modules of an immune system (immunoglobulin like molecules, scavenger receptor
cysteine-rich, and short consensus repeats, rhesus system) classify the Porifera as true Metazoa. As living fossils, provided
with simple, primordial molecules allowing cell-cell and cell-matrix adhesion as well as processes of signal transduction
as known in a more complex manner from higher Metazoa, they also show peculiarities not known in other metazoan phyla. Tissues
of sponges are rich in telomerase activity, suggesting a high plasticity in the determination of cell lineages. It is concluded
that molecular biological studies with sponges as model will not only help to understand the evolution of Protoctista to Metazoa
but also the complex, hierarchial regulatory network of cells in higher Metazoa. 相似文献
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Sperm competition is thought to be an important selective pressure shaping sperm form and function. However, few studies have
moved beyond gross examinations of sperm morphology. Sperm length is subject to sexual selection via sperm competition in
the scarab beetle Onthophagus taurus. Here, the structure and ultrastructure of spermatozoa in this species were investigated using light and electron microscopy.
Spermatozoa were found to be filiform, measuring about 1,200 mm in length. The sperm head consists of a three-layered acrosome
and a nuclear region bearing the anterior extension of the centriole adjunct. Acrosome and nuclear regions are bilaterally
symmetric, with their axes of symmetry being orthogonal to each other. Head and flagellar structures are connected by a well-developed
centriole adjunct. The sperm heads are asymmetrically surrounded by accessory material and embedded into the cytoplasm of
the spermatocyst cell. The accessory material is produced inside the spermatids and then transferred to the outside due to
a new membrane formed around the sperm’s organelles. The old spermatid membrane separates the accessory material from the
cyst cell. The flagellum contains a 9+9+2 axoneme, two accessory bodies, and two mitochondrial derivatives of unequal size.
The major mitochondrial derivative is significantly larger than the minor one. The axoneme is arranged in a sinusoidal manner
parallel along the major mitochondrial derivative. The spermatozoa show no progressive motility when released in buffer solution
which is likely to be the result of the flagellar arrangement and the structure of the major mitochondrial derivative. The
cross-sectional area of the minor and the major mitochondrial derivatives show different patterns of genetic variation. The
data provide the first estimates of genetic variation in sperm ultrastructure for any species, and give evidence for the persistence
of genetic variation in ultrastructure required for the rapid and divergent evolution that characterizes spermatozoa generally. 相似文献