Fig. 3.

The effect of mean temperature on mean fire size during early-season burning in P. mariana–feathermoss forests of eastern boreal North America. Fire data were those of the Ministère des Ressources Naturelles et de la Faune du Québec. The period of analysis is from 1973 to 2009. Mean fire size was computed for 18 early seasons (April to June), using a minimum threshold of n = 10 fires y⁻¹; those seasons in which the number of fires was below this threshold were excluded from analysis. Ignition of 95% of the sampled fires took place after May 27th (n = 740 fires in total; Lower, sample distributions; correlation between n and mean fire size is Spearman’s r = 0.232, P = 0.347). Error bars represent 90% confidence intervals for the means obtained by bootstrap resampling of the fire samples. The dashed line represents the exponential regression of mean fire size on mean temperature. Temperature data (land only) were those of Climate Research Unit TS 3.1 (32), averaged over the domain encompassing 79.5°W–70.0°W and 48.5°N–52.5°N.