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The effect of litter quality and climate on the rate of decomposition of plant tissues was examined by the measurement of mass remaining after 3 years’ exposure of 11 litter types placed at 18 forest sites across Canada. Amongst sites, mass remaining was strongly related to mean annual temperature and precipitation and amongst litter types the ratio of Klason lignin to nitrogen in the initial tissue was the most important litter quality variable. When combined into a multiple regression, mean annual temperature, mean annual precipitation and Klason lignin:nitrogen ratio explained 73% of the variance in mass remaining for all sites and tissues. Using three doubled CO2 GCM climate change scenarios for four Canadian regions, these relationships were used to predict increases in decomposition rate of 4–7% of contemporary rates (based on mass remaining after 3 years), because of increased temperature and precipitation. This increase may be partially offset by evidence that plants growing under elevated atmospheric CO2 concentrations produce litter with high lignin:nitrogen ratios which slows the rate of decomposition, but this change will be small compared to the increased rate of decomposition derived from climatic changes.

Perennially frozen peatlands were divided into five morphological types: peat plateaus, polygonal peat plateaus, palsas, fen ridges and lowland polygons. One hundred and eight different peatlands were cored, measured and sampled. The internal structure of all but the lowland polygons suggests that the peat was deposited in wet fens unaffected by permafrost, and that permafrost developed only after a thin layer of Sphagnum covered them. The lowland polygons evolved in a permafrost environment. The study area was divided into four regions oh the basis of predominance of different peatlands forms.

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A phytogeoclimatic study of the high subarctic region of Canada between Hudson Bay and the Cordillera at the northern Yukon-Mackenzie border was undertaken to provide a verifiable and quantitative synthesis of forest-tundra vegetation ecology. Three field seasons of vegetation and terrain studies provided ground truth for a grid of 1314 black-and-white air photos that cover Ca. 24% of the forest-tundra and adjacent low Subarctic and low Arctic. Air photos were analyzed for percentage cover of nine vegetation-terrain types, bedrock and parent materials, landforms, and elevations. The forest-tundra, as bounded by the 1 O : l and 1:lOOO tree:upland tundra cover isolines, spans an average 145 f 72 km (median 131 km) and increases in width from northwest to southeast. The transition from 101 to 1:lO treexpland tundra cover occupies one-fourth to one-half the area of the forest-tundra. Regional slope of the land probably accounts for much of the variation in width of the forest-tundra. Southern outliers of forest-tundra in the northwest are found mainly in areas of high elevation. Across much of the northwest, steep vegetation gradients occur near the northern limit of trees. North of Great Slave Lake, steep vegetation gradients shift from the northern to the southern half of the forest-tundra and maintain this position eastward to Hudson Bay. The forest-tundra of the northwest receives roughly three-fourths the mean annual net radiation available to the southeast and central districts.

This paper examines the impact that climatic change over the last millennium has had on aggradation and degradation of permafrost peatlands and the associated change in organic matter accumulation. Permafrost reached its southernmost Holocene extent in boreal continental western Canada during the Little Ice Age with 28 800 km2 of permafrost peatland present within a sensitive zone demarcated by permafrost degradation. Subsequent degradation of permafrost has occurred in response to warming, with forested bogs changing to nonforested poor fens, associated with rising water levels. In conjunction with this ecosystem change, long-term net organic matter accumulation increases. As permafrost is in disequilibrium with climate, much of the permafrost that remains is in a relict state. Mapping of past and present permafrost distribution from peatland landforms indicates only 9% has degraded since the Little Ice Age, resulting in a 5% increase in long-term net organic matter accumulation. Of the permafrost that remains, 22% is in disequilibrium, located largely in the northern part of the sensitive zone. Additional loss of forested lands will occur in the future in boreal continental western Canada under present-day climatic conditions as permafrost approaches equilibrium, with a further 11% increase in long-term net organic matter accumulation predicted.

Boreal peatlands occupy about 1.14 x 106 km2 in North America. Fires can spread into peatlands, burning the biomass, and if moisture conditions permit, burning into the surface peat. Charred layers in peat sections reveal that historically bogs in the subhumid continental regions and permafrost peatlands of the subarctic regions have been the most susceptible to fires. Fire return periods were estimated from the numbers and ages of the charred peat layers. Based on average moisture conditions of the surface, about 0.5% of the peatlands (6420 km2) can be expected to burn annually, but the surface peat layer is expected to burn only in a small portion of this area (1160 km2). Carbon losses from aboveground combustion, in the form of CO2, CO, CH4, and nonmethane hydrocarbons, are the highest in forested swamps at 2.03 Tg C ·year-1. Carbon losses due to combustion of surface peat is the highest in the driest peatlands (e.g., raised bogs underlain by permafrost) at 5.82 Tg C ·year-1. The total estimated carbon release due to aboveground combustion is 2.92 Tg C ·year-1 and due to belowground peat combustion is 6.72 Tg C ·year-1. These estimates of direct carbon emissions to the atmosphere due to wildfires suggest a globally significant, but relatively small source in contrast with emissions from wildfires in uplands. The effects of a possible climate change are expected to be most prominent in the continental and northern parts of North America. A lower water table would result in increased CO2 but decreased CH4 emissions from the peatlands. A drier climate may mean increased fire frequency and intensity, resulting in more fires in peatlands and an increased probability of the fires consuming part of the peat.Key words: fire, peatlands, carbon, boreal, permafrost, gas flux.