Multi‐millennial fire frequency and tree abundance differ between xeric and mesic boreal forests in centralCanada

Abstract

SummaryMacroscopic sedimentary charcoal and plant macroremains from two lakes, 50 km apart, in north‐westernOntario,Canada, were analysed to investigate fire frequency and tree abundance in the central boreal forest. These records were used to examine the controls over the long‐term fire regime, and vegetative dynamics associated with fire return intervals (FRIs).There were 52 fire events atLakeBen (surrounded by a xeric landscape) between 10 174 calibrated years before present (cal. yearbp) and the present with an averageFRIof 186 years with values oscillating between 40 and 820 years. Forty‐three fire events were recorded atLakeSmall (surrounded by a mesic landscape) between 9972 cal. yearbpand the present with an averageFRIof 229 years and a range of 60–660 years.FRIs atLakeSmall decreased significantly afterc. 4500 cal. yearbp, whereas atLakeBenFRIs remained similar throughout theHolocene. DifferentFRIdistributions and independence in the occurrence of fire events were detected between 10 000 and 4500 cal. yearbpfor the two sites. Between 4500 cal. yearbpand the present, similarFRIs were observed, but fires continued to occur independently.LongerFRIs resulted in declining abundance ofLarix laricinain both landscapes. LongerFRIs resulted in a decline in the abundance ofPicea marianain the xeric landscape, but a marginal increase in the mesic landscape. Abundances ofPinus banksiana,Pinus strobusandBetula papyriferawere unrelated toFRI, underlying that these species maintain their local abundance irrespective of fire frequency.Synthesis. Our results show contrasting fire regime dynamics between a xeric and mesic landscape in central boreal forests,Canada. These results highlight the influence of local factors as important drivers of fire frequency at centennial to millennial scales. Local site factors, especially soil moisture, need to be incorporated into predictive models of vegetation response to climate change.