Post-Glacial Climate-Fire Interactions Control Tree Composition of Mesic Temperate Forests in Eastern North America

Stand-scale gap-phase dynamics is generally viewed as the main driver of development in mesic deciduous forests of the temperate biome. Soil charcoal of temperate forests in eastern North America are unnoticed in most surveys, thus explaining why fire is undervalued as a driver of forest succession. The extent to which gap-phase, fire, or other processes are responsible for the regeneration and maintenance of mesic deciduous forests is unknown because paleoecological evidence is lacking. We tested the fire-driven succession hypothesis on the development of this major forest type. Based on charcoal C-14 dates of two sites, 44 and 55 fires occurred since early Holocene, with a mean interval of 170 to 215 years. The vegetation of both sites followed comparable post-glacial trajectories consisting of three distinct periods. Conifers dominated the two first periods during 5200-6000 years and were replaced by hardwoods-conifers over the last 3500 years. The first period was represented by boreal conifers, whereas the second period, dominated by white pine (Pinus strobus) forests, persisted during 3000-4300 years. The third period marked the development of hardwood (sugar maple, Acer saccharum) forests. Fires occurred continuously on the sites since early Holocene likely under dry conditions during the conifer periods and cooler and moister conditions during the hardwood-conifer period. Recurrent fires appear with climate as key drivers of the long-term dynamics of several temperate forests in eastern North America. Similar studies on other temperate forests should be pursued to test the hypothesis of climate-fire interactions influencing tree composition change.