Regional variation in the proportion of red heartwood in sugar maple and yellow birch

Stems of sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britt.) trees often contain a column of discoloured wood known as red heartwood, which reduces lumber value. To quantify the regional-scale variation in red heartwood, 192 trees of each species were sampled in 12 locations across the temperate forest zone of southern Québec, Canada. Large regional variation in the radial proportion of red heartwood (RHP) at breast height (1.3 m) was observed in both species. Statistical modeling showed that such variation was mainly attributable to factors related to tree development. Cambial age had a strong positive effect on RHP in both species, suggesting that the occurrence of red heartwood ultimately might be unavoidable. There was also a positive effect of ring area increment at the limit of the discoloured zone. In the case of sugar maple, there was an added effect of the trend in ring area increments observed in the same zone, with a negative trend being generally indicative of a larger RHP. Further variability in this species was also associated with the annual minimum temperature of the sampling locations. The models developed for each species explained around 60% of the variance in RHP and could be used to improve forest management and wood procurement decisions.