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Technical Thematic Report No. 9. - Trends in permafrost conditions and ecology in northern Canada

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Trends in permafrost conditions and ecology in northern Canada

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S. SmithFootnote[1]

Canadian Biodiversity: Ecosystem Status and Trends 2010
Technical Thematic Report No. 9
Published by the Canadian Councils of Resource Ministers

Library and Archives Canada Cataloguing in Publication

Trends in permafrost conditions and ecology in northern Canada.

Issued also in French under title:
Tendances relatives aux conditions du pergélisol et à l’écologie dans le nord du Canada.
Electronic monograph in PDF format.
ISBN 978-1-100-19094-5
Cat. no.: En14-43/9-2011E-PDF

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This report should be cited as:

Smith, S. 2011. Trends in permafrost conditions and ecology in northern Canada. Canadian Biodiversity: Ecosystem Status and Trends 2010, Technical Thematic Report No. 9. Canadian Councils of Resource Ministers. Ottawa, ON. iii + 22 p.

© Her Majesty the Queen in Right of Canada, 2011
Aussi disponible en français

Footnotes

Footnote 1

Geological Survey of Canada, Natural Resources Canada

Return to footnote 1

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Preface

The Canadian Councils of Resource Ministers developed a Biodiversity Outcomes FrameworkFootnote1 in 2006 to focus conservation and restoration actions under the Canadian Biodiversity Strategy.Footnote2 Canadian Biodiversity: Ecosystem Status and Trends 2010Footnote3 was a first report under this framework. It assesses progress towards the framework’s goal of “Healthy and Diverse Ecosystems” and the two desired conservation outcomes: i) productive, resilient, diverse ecosystems with the capacity to recover and adapt; and ii) damaged ecosystems restored.

The 22 recurring key findings that are presented in Canadian Biodiversity: Ecosystem Status and Trends 2010 emerged from synthesis and analysis of technical reports prepared as part of this project. Over 500 experts participated in the writing and review of these foundation documents. This report, Canadian climate trends, 1950-2007, is one of several reports prepared on the status and trends of national cross-cutting themes. It has been prepared and reviewed by experts in the field of study and reflects the views of its authors.

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Acknowledgements

Support has been provided by Natural Resources Canada and the Federal Government’s International Polar Year Program. I also thank the reviewer of this report.

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Ecological Classification System – Ecozones+

A slightly modified version of the Terrestrial Ecozones of Canada, described in the National Ecological Framework for CanadaFootnote4, provided the ecosystem-based units for all reports related to this project. Modifications from the original framework include: adjustments to terrestrial boundaries to reflect improvements from ground-truthing exercises; the combination of three Arctic ecozones into one; the use of two ecoprovinces – Western Interior Basin and Newfoundland Boreal; the addition of nine marine ecosystem-based units; and, the addition of the Great Lakes as a unit. This modified classification system is referred to as “ecozones+” throughout these reports to avoid confusion with the more familiar “ecozones” of the original framework.Footnote5

Ecological classification framework for the Ecosystem Status and Trends Report for Canada.

map

Long Description for Ecozones+ map of Canada

This map of Canada shows the ecological classification framework for the Ecosystem Status and Trends Report, named “ecozones+”. This map shows the distribution of 15 terrestrial ecozones+, two large lake ecozones+, and nine marine ecozones+.

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Introduction

Permafrost is soil, rock, or sediment that remains at or below a temperature of 0°C for at least two consecutive years. Permafrost has an important influence on the biophysical environment and processes largely because it can contain ice as pore ice, ice lenses, ice wedges, and other massive ice bodies (Mackay, 1972). The permafrost region covers about half the Canadian landmass (Figure 1). In the northern portion of the permafrost region, permafrost is continuous and may be several hundred metres thick and have temperatures colder than −5°C (Heginbottom et al., 1995; Smith et al., 2001a). Further south, permafrost becomes discontinuous and patchy, is only a few metres thick and persists at temperatures approaching 0°C (for example Smith et al., 2008).

Figure 1. Permafrost map for Canada.

map

Long Description for Figure 1

This map shows the permafrost region for Canada, displayed as four permafrost zones. The continuous permafrost zone includes the Arctic, most of the Taiga Cordillera, and the northern portions of the Taiga Plains, Taiga Shield, and Hudson Plains ecozones+. The extensive discontinuous permafrost zone includes the northern portion of the Boreal Cordillera, the Great Bear and Great Slave lake regions, runs south of the Hudson Bay and along the north border of east Taiga Shield. The sporadic permafrost zone includes the southern portions of the Boreal Cordillera, Taiga Plains, Hudson Plains, and Taiga Shield ecozones+, and extends as far south as the northern portions of the Pacific Maritime, Montane Cordillera, Boreal Plains, and Boreal Shield ecozones+. The mountain permafrost zone includes the southern portion of the Montane Cordillera Ecozone+ and parts of the Pacific Maritime, Atlantic Maritime, and Newfoundland Boreal ecozones+.

Source: adapted from Heginbottom et al. (1995)

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The active layer is the upper part of the ground that thaws each summer and refreezes in the winter. The active layer overlies permafrost and its thickness is influenced by a number of factors, including climate and local factors such as snow cover, vegetation, presence of an organic layer, soil moisture conditions, and surficial materials (Smith et al., 2001a). Active layer thickness can vary from less than 0.5 metres in vegetated organic terrain to several metres in areas of exposed bedrock (Smith et al., 2001a). Moisture and gas fluxes are generally confined to the seasonally-thawed active layer. Permafrost and the characteristics of the active layer therefore can influence both physical and chemical processes. These processes interact and, along with climate, they shape the landscape, vegetative communities, and ecosystems from the boreal forests to the tundra (for example Mackay, 1995; Walker et al., 2004; Kokelj and Burn, 2005; Lewkowicz and Harris, 2005; Kokelj et al., 2007a).

Changes in both the areal extent and thickness of permafrost have occurred in the past in response to changes in climate occurring at scales of decades to centuries to millennia. Permafrost increases in areal extent and thickens under a cooling climate, while a warming climate results in thickening of the active layer and thinning or even disappearance of permafrost. Changes in permafrost conditions over the past several thousand years are discussed by Smith and Burgess (2004) and Smith et al. (2001a). Under warmer conditions during the mid-Holocene, 6,000 to 9,000 years ago, the southern limit of permafrost was north of its present position and active layers were generally thicker where permafrost was present (for example Burn et al., 1986; Zoltai, 1995). Following the mid-Holocene Warm Period, cooler conditions about 3,700 to 5,000 years ago resulted in an increase in permafrost extent (for example Zoltai, 1993; Vardy et al., 1998).

During the Little Ice Age between 1550 AD and 1850 AD, air temperatures were about 1°C colder and permafrost occurred farther south than at present (for example Vitt et al., 1994). At the southern fringes of the discontinuous permafrost zone, some of this permafrost persists in organic terrain, in particular Sphagnum-dominated peatlands (Halsey et al., 1995). Permafrost has been preserved under warmer present day climate conditions by a thick layer of insulating peat. More recently over the past two to three decades, warming of permafrost has been observed across the permafrost regions. Further discussion of more recent changes in permafrost conditions is found below.

Changes in permafrost conditions are expected over the next century in response to climate warming. Warmer and thinner permafrost in the southern portion of the discontinuous permafrost zone may ultimately disappear under anticipated climate warming, while in areas of thicker and colder permafrost, warming will likely result in thickening of the active layer and a decrease in permafrost thickness (Smith and Burgess, 2004). Simulations at a circumpolar scale project increases in active layer thickness of 20 to 60% over the next century (ACIA, 2005). However, models at these scales often use generalized representations for vegetation conditions and characteristics of earth materials which are important influences on the thermal response of permafrost. Results of modeling studies in the boreal and tundra environments of the Mackenzie Valley region, an area where recent increases in air temperature have been the greatest, indicate that thaw depths will increase 15 to 40% over the next century in response to climate warming, with smaller increases occurring where a thick organic layer is present (Woo et al., 2007).

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Footnotes

Footnote 1

Environment Canada. 2006. Biodiversity outcomes framework for Canada. Canadian Councils of Resource Ministers. Ottawa, ON.p. Environnement Canada. 2006.

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Footnote 2

Federal-Provincial-Territorial Biodiversity Working Group. 1995. Canadian biodiversity strategy: Canada's response to the Convention on Biological Diversity. Environment Canada, Biodiversity Convention Office. Ottawa, ON. 80 p.

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Footnote 3

Federal, Provincial and Territorial Governments of Canada. 2010. Canadian Biodiversity: Ecosystem Status and Trends 2010. Canadian Councils of Resource Ministers. Ottawa, ON. vi + 142 p.

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Footnote 4

Ecological Stratification Working Group. 1995. A national ecological framework for Canada. Agriculture and Agri-Food Canada, Research Branch, Centre for Land and Biological Resources Research and Environment Canada, State of the Environment Directorate, Ecozone Analysis Branch. Ottawa/Hull, ON. 125 p. Report and national map at 1:7 500 000 scale.

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Footnote 5

Rankin, R., Austin, M. and Rice, J. 2011. Ecological classification system for the ecosystem status and trends report. Canadian Biodiversity: Ecosystem Status and Trends 2010, Technical Thematic Report No. 1. Canadian Councils of Resource Ministers. Ottawa, ON.

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Introduction