Fire-controlled variations in abundance of white pine and red pine in Quebec’s northern temperate forest during the Holocene: Implications for fire management

In North American temperate forests, white pine ( Pinus strobus L.) and red pine ( Pinus resinosa Ait.) establish on sites cleared by infrequent high-severity crown fires and persist in the long-term when low-severity surface fires clear the understory and expose mineral seedbeds, facilitating regeneration. Considerable reduction of white pine and red pine abundance over the last two centuries due to overharvesting and fire suppression prompted experiments with prescribed burning. In La Mauricie National Park (LMNP; southern Québec, Canada) all natural fires have been actively suppressed since the 1970s, and only prescribed (surface) burns occurred since the 1990s. Taking advantage of this unique setting, we quantified charcoal particles in the sediments of three lakes within LMNP to identify a tentative charcoal accumulation threshold differentiating surface fires from crown fires. We then compared the signal left by the current regime of surface fires with the fire regimes of other periods of the Holocene. Based on the threshold, we showed that a mixed regime of frequent low-severity surface fires and infrequent high-severity crown fires was associated to high abundance of white pine and red pine during the Holocene Thermal Maximum (ca. 8400–4500 cal. yr BP). Regimes of only surface fires during the early neoglacial period (ca. 4500–1500 cal. yr BP) or only crown fires during the early Holocene (before 8400 cal. yr BP) were less conducive to the establishment and persistence of white pine and red pine. Instead of systematically suppressing crown fires, they should be allowed to burn while protecting infrastructures.