C concentration observed in aspen and birch, not jack pine, which
had the highest mean volatile C concentration of all species at
7.5 ± 0.2% (S.E.) (Table 2). In addition, interactions between shade
tolerance and tree size, and between species and tree size, had significant
effects on volatile C concentration (Table 3). For shadeintolerant
trembling aspen and white birch, volatile C concentration
in bark showed a marginal (P = 0.092 and 0.062, respectively)
positive trend with tree size (Fig. 1). Volatile C of bark marginally
decreased with DBH for shade-tolerant white spruce, and significantly
decreased with DBH for balsam fir (Fig. 2).