The post-fire shift of temperate white pine-birch forest to boreal balsam fir forest in eastern Canada: climate-fire implications

Abstract

11Extensive 14C dating and botanical identification of charcoal fragments located in the 12 organic soil surface and buried in the mineral podzolic solum were used to reconstruct the 13 successional pathways of a balsam fir forest site. The studied forest site developed in a 14context of continuous fire disturbance over the last 9000 years with at least 26 fires 15 occurring at a mean interval of 330 years. Tree vegetation of the site followed a four-step 16 trajectory consisting of an early-Holocene spruce forest and a late-Holocene mixedwood 17 balsam fir forest. Boreal-like spruce-birch and temperate-like white pine-birch forests 18dominated the site between 7900-5900 cal. BP and 5600-1275 cal. BP, respectively.19because all forest types developed repeatedly after fire since early deglaciation, changes 20 in forest composition, in particular the shift of white pine forest to balsam fir forest, and 21 concurrent decline of birch (yellow birch and/or paper birch) and pine populations, were 22 most likely related to progressive cooler and wetter conditions from mid- to late23Holocene. Fire disturbance on this part of the southern boreal biome has been a24continuous, positive regenerative process over the Holocene allowing the successional