Age structure of red pine (Pinusresinosa Ait.) at its northern limit in Quebec

Abstract

At the northern limit of red pine (Pinusresinosa Ait.) fire may be of critical importance in determining the persistence of red pine and its restriction to islands and shores of lakes. The objectives of the study were to document the distribution pattern of red pine populations of the Lake Duparquet area in northwestern Quebec and to analyze the age structure and fire history of the populations. The combined age structure of 22 red pine populations is balanced and uneven aged, with two periods of increased recruitment from 1805 to 1864 and from 1925 to 1974. The analysis of individual populations indicates that they can be separated into three groups associated with specific site conditions: (i) uneven-aged populations with constant recruitment occurring on xeric sites, (ii) even-aged populations without regeneration occurring on mesic sites, and (iii) uneven-aged populations, showing both a constant recruitment and peak periods of regeneration, occurring on sites with xeric and mesic portions. Although all fires registered, lethal and nonlethal, are generally asynchronous between sites, the fires of 1825 and 1944 seem to have affected large areas of the lake. Two mechanisms for the maintenance of red pine were detected: self-regeneration of populations resistant to fires on xeric sites, and the transitory colonization of mesic sites by populations susceptible to lethal fires and established by seed from distant seed sources. Red pine may be restricted to lake landscapes because of the abundance of sites protected from lethal fires.