PARENT SESSION
Organized Oral Session 32: Forest disturbance regimes in the circumboreal forest zone: Natural variability and implications for forest management and biodiversity conservation
Organizer(s): S Gauthier, T Kuuluvainen, and D Kneeshaw
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 516 C, Level 5, Palais des congrès de Montréal

Natural disturbance dynamics in the boreal plains of central Canada.

Tardif, Jacques¹, ¹ Centre for Forest Interdisciplinary Research (C-FIR), Winnipeg, Manitoba, Canada

ABSTRACT- A growing interest in the development of management practices that are based on understanding natural disturbance is currently observed. Integrating natural disturbance and forestry practices has been proposed as a way to better maintain biodiversity at the landscape level. Little research has been conducted in Central Canada with regards to natural disturbances. Both the fire history and the forest tent caterpillar outbreaks were reconstructed for the Duck Mountain Provincial Forest (DMPF), western Manitoba. The DMPF is unique with respect to i) its isolated nature along the Manitoba escarpment and ii) the existence of a provincial park within its boundaries. Dendrochronological evidences suggest that large, but infrequent fires associated with severe drought period have dominated before European settlement. The imprint of the late 19th century fires (about 80% of the landscape was affected by catastrophic fires occurring from 1885-1895) coupled with European settlement and fire suppression constitute the dominant forces structuring the ecological processes of today. In the DMPF, the mean age of the forests is about 110 years and the current level of diversity may not constitute a benchmark by which we can assess the impact of forest management. The last major fire to burn in the DMPF was in 1961, a year of severe drought also marking the onset of a severe forest tent caterpillar (FTC) outbreak. Tree-ring evidences suggest that major periods of FTC outbreaks occurred from 1939 to 1948, 1961 to 1965 and 1982 to 1985, with an additional large-scale outbreak suspected during the 1870s. Major outbreaks of the 20th century started in the north and spread into the DMPF at different rates. The impacts of repeated FTC outbreaks on forest dynamics and productivity need to be better assessed. In an aging forested landscape, FTC outbreaks may play a role in speeding-up succession toward a larger importance of conifers in the landscape. Our study emphasizes the need to reintroduce larger scale disturbances in the DMPF and questions our ability to cope with potential risk associated with large, infrequent disturbances. While silviculture practices can be adapted to replicate smaller scale disturbances, it may be required to also adapt them to alter the vulnerability to catastrophic fires in a context of sustainable forest management.

Key words: Forest fire, Forest tent caterpillar, Dendrochronology, Forest management