摘要:

Boreal forest fire regime, which encompasses fire intensity, frequency, seasonality, size, type (crown versus surface), and severity (depth of burn), is an organizing factor of boreal forest landscapes and highly dependant on climate. This review combines what is known about boreal forest dynamics from paleological studies, with the information derived from state-of-the-art climate and vegetation modeling, to present possible scenarios of the impact of anticipated climate change on boreal forest ecosystem structure and function, particularly in relation to fire regimes. Anticipated climatic/atmospheric impact on plant physiological, communal, ecosystem, and finally landscape-level interactions with fire are reviewed. All indications from the modeling sector point towards unprecedented increased regional or seasonal temperatures, with projected changes most pronounced at high latitudes and there greatest in winter. Anticipated climate change scenarios are expected to alter dramatically the boreal forest ecosystems and fire regimes with which they are currently in equilibrium. Changed fire regimes could be represented by increased annual area burned because of an extended fire season, increased fire frequency, and severity. Simulation studies show the potential for greatly reduced boreal forest area and increased fragmentation due to climate change. Fire regime as an ecosystem process is highly sensitive to climate change because fire behaviour responds immediately to fuel moisture, which is affected by precipitation, relative humidity, air temperature, and wind speed. This interaction between climate change and fire regime has the potential to overshadow the importance of the direct effects of global warming on species distribution, migration, substitution, and extinction. Such a scenario suggests that rate and magnitude of fire-regime-induced changes to the boreal forest landscape could greatly exceed anything expected due to atmospheric warming alone. Socioeconomic implications of altered fire regimes in a changing climate are discussed in terms of adaptive fire management strategies, age class distribution, and such global stewardship issues as biodiversity, carbon cycling, and sequestration.

ISSN:1208-6053    

DOI:10.1139/a97-008

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

We conducted a systematic review of English-language analytical epidemiological studies assessing whether contaminants from hazardous waste sites cause adverse human health effects. From 900 candidate studies identified from computerized searches, bibliographic reviews, reference lists, and personal contacts, 43 potentially eligible studies were chosen. These were independently screened by two reviewers and 14 studies were selected for the final review. Each study was assessed independently by three reviewers. The methodology and main results were summarized. Studies were rated for different aspects of internal validity and criteria for causation. Inter-rater reliability was evaluated and differences were resolved by consensus. Most (11 of 14) studies selected for the final review were case-control studies. Hazardous exposures ranged from a single chemical in groundwater to multiple compounds in contaminated landfill sites. Health outcomes assessed included various cancers, various reproductive outcomes, and a variety of nonspecific health conditions and symptoms. Reported statistically significant relative risks (RRs) or odds ratios (ORs) were generally modest. Overall, for these 14 studies exposure measures were poorly rated; outcome measures were well rated and measurement bias, selection bias, and confounding biases were intermediately rated. Adherence to criteria for temporal association and biological plausibility was better than for other criteria of causality. The studies reviewed did not provide convincing evidence of causal relationships between hazardous waste site exposure and adverse human health effects, in particular because of poor exposure measurement. This does not mean that such causal relationships do not exist. Substantially better exposure assessment methodology is needed to establish the harmful effects caused by hazardous waste exposures.

ISSN:1208-6053    

DOI:10.1139/a97-009

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Dendrochemical techniques have been used to monitor historical changes in soil and atmospheric chemistry since the early 1970s. The development of dendrochemistry in environmental monitoring was prompted by early studies which reported that changes in Pb deposition along roadsides and in industrial areas were reflected by changes in the Pb content of tree rings. Early studies were inconclusive; some authors have stated that tree-ring chemistry is not a useful indicator of pollution episodes and that some tree species are clearly better spatial indicators of pollution than historical monitors. This is due to a number of complicating factors, including potential radial translocation of elements, radial tendencies in element concentration from pith to bark, and physiological differences between heartwood and sapwood. A more detailed understanding of element cycling in trees is needed, as at present, the application of dendrochemistry to historical environmental monitoring is strongly dependent on the choice of tree species and the elements to be studied. There is no general consensus as to which tree species are best suited for dendrochemical studies. There are many reports in which the analyses of tree-ring chemistry have been successfully used to reconstruct trace-metal deposition from a variety of sources, including automobiles, metal refineries, and coal burning. Changes in tree-ring chemistry in recent decades have coincided with hypothesized changes in soil chemistry believed to be a result of acidic deposition onto poorly buffered soils. Indications of changes in groundwater quality, volcanic eruptions, and even climate change have been reported to be preserved in the chemical composition of tree rings. An improvement in analytical techniques has allowed multielement analysis on whole wood samples, with very low detection limits and extremely high spatial resolution, enabling intra-annual changes in element composition of tree rings to be determined. The application of dendrochemistry in environmental monitoring is promising, and with a more detailed understanding of nutrient and metal cycling in trees, dendrochemical studies will continue to provide useful information on historical pollution loadings and changes in soil and atmospheric chemistry that is unobtainable from any other source.

ISSN:1208-6053    

DOI:10.1139/a97-010

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The human health consequences of the Chernobyl accident in 1986 have been the subject of a great many studies. Many of the findings and opinions were brought together at a major international conference held in Minsk in 1996. The overall findings from this workshop are discussed with particular focus on thyroid cancers and exposures to iodine-131.

ISSN:1208-6053    

DOI:10.1139/a97-011

出版商:NRC Research Press    

年代:1997

数据来源: NRC

ISSN:1208-6053    

DOI:10.1139/a97-012

出版商:NRC Research Press    

年代:1997

数据来源: NRC