Payette, S., Filion, L. and Delwaide, A. 2008. Spatially explicit fire-climate history of the boreal forest-tundra (Eastern Canada) over the last 2000 years. Philosophical Transactions of the Royal Society B 363: 2301-2316.
What was done
Based on several years of field investigations designed to exhaustively map and accurately date the occurrences of all fires per each 100-year interval over the last 2000 years of a 40-km2 area of northern boreal forest-tundra within the Riviere Boniface watershed in northeastern Canada (57°45'N, 76°W), the authors developed a long-term, spatially-explicit fire history of the northernmost boreal forest in that region.
What was learned
Payette et al. report there was a "70% reduction of forest cover since 1800 yr BP and nearly complete cessation of forest regeneration since 900 yr BP," such that "the northern part of the forest tundra in Eastern Canada has been heavily deforested over the last millennium," while further noting that "the climate at the tree line was drier and warmer before 900 cal. yr BP."
What it means
The chief direct cause of the post-900 yr BP deforestation, in the words of the three Canadian researchers, was "climate deterioration coinciding with the phasing-out of the Medieval Warmth and incidence of the Little Ice Age." In addition, they say that since "the latitudinal position of successful post-fire regeneration of lichen-spruce woodlands is situated approximately 1.5° south of the Boniface area, as a rule of thumb it is probable that a drop of at least 1°C in mean annual temperature occurred after 900 cal. yr BP." As a result they state that "recovery of the boreal forest after a long period of deforestation will require sustained warming," which they add has only been occurring "since the mid-1990s in Eastern subarctic Canada." Hence, it would appear that this particular part of North America has not yet experienced a sustained warming of magnitude great enough to return it to Medieval Warm Period conditions.