Reconstructing the recent dynamics of mires using a multitechnique approach

Abstract

1. The recent vegetation dynamics of 16 ombrotrophic mires in southern Québec (Canada) was studied through palaeoecological (dendrochronology, plant macrofossil and pollen analyses) and historical (aerial photograph analyses) techniques. 2. Plant macrofossil analyses show that prior to European colonization (c. 1800), mires were predominately open environments dominated by Sphagnum mosses. Many sites subsequently became forested with little or no Sphagnum. 3. Aerial photograph analyses indicate that widespread forest expansion occurred in all mires between 1948 and 1995. The percentage of the total mire area occupied by forest increased from 22.5 to 56.5%, an overall gain of 137 ha of forest habitat. 4. A dry climatic period during the first part of the 20th century, drainage resulting from human activities, and fire events, seem to be the main causal factors of vegetation changes. 5. Forest expansion is expected to cause profound changes in bog ecosystems, such as altering hydrological conditions and organic accumulation processes, and to be detrimental to regional biodiversity and the carbon balance. 6. Overall, this study highlights the need to incorporate multiple approaches in reconstructing the vegetation dynamics of an ecosystem, and in determining causal factors of vegetation change.