Miscellaneous

Time since fire map, age-class distribution and forest dynamics in the Lake Abitibi Model Forest.

By Sylvie Gauthier, Patrick Lefort, Yves Bergeron and Pierre Drapeau

The report is one in a series of publications produced by the Laurentian Forestry Centre, and is generating considerable interest, and many requests for copies. It focuses on mapping fire history in the Lake Abitibi Model Forest, and the role that fire has played in the forest’s current structure. It also presents some sustainable forest management considerations based on this fire disturbance history.

The report presents details and results of a study on the fire history and forest dynamics within the Lake Abitibi Model Forest. Using aerial photographs, archival documents, and field sampling, the study team created a ‘time since fire map’ for the entire landbase. The production of the map allowed the calculation of age class distribution, the size distribution of stands, the forest composition in each age class, and the fire cycle for different time periods (e.g. the time needed to burn an area equal in size to the study area). Results indicate that large parts of the Lake Abitibi Model Forest have not burned for long periods of time. This suggests that fires have generally been large and that time between fires is long. During the past 300 years, the forest fire cycle length has significantly increased from less than 100 years before the year 1850, to more

than 400 years after the year 1920. It was also found that forest stands that have not burned for more than 100 years represent 78% of the studied area, with some portions not having burned for 200 or even 250 years. Jack pine, poplar and white birch species occupy larger areas in sites that have burned within the last 100 years than in the older sites, while black spruce and balsam fir species are more common in sites older than 100 years. The mean time since fire for forest stands is 172 years, suggesting that the global fire cycle is longer than the normal rotation of the studied area. The differences between a natural age class distribution and an even-aged forest must be considered in management activities. Even-aged management tends to decrease the amount of old forest, one of several landscape types important in maintaining biodiversity. However, the longer rotations that would be prevalent with a natural age class distribution (uneven-aged management) could lead to a decrease in allowable cut. By using different treatments and practices that conserve certain structural characteristics of older stands, a reconciliation of these two issues may be possible. Newer practices such as HARP that are currently being used in the Lake Abitibi Model Forest may contribute positively to this approach.

Available from the Lake Abitibi Model Forest Office.