Growth-mortality attributes and species composition determine carbon sequestration and dynamics of old stand types in the Acadian Forest of New Brunswick, Canada

Abstract

Key message: We used 20 years of plot data to analyze the influence of tree growth-mortality balance and species mix on the potential of old stands to sequester carbon from the atmosphere and store carbon. The study indicated that carbon in hardwood-dominated stands increased with age, without any sign of decline in carbon sequestration. In contrast, balsam fir (Abies balsamea(L.) Mill.) dominated softwood stands showed a negative C change with a decline at 80 years of age. Context: Variation in species stand development, carbon (C) storage, and sequestration is fundamental to ascertain the role of old forests as sources and sinks in global C. Aims: To analyze the effect of the balance between growth and mortality of species and hardwood-softwood mix on the C source and sink budget of old forest types in New Brunswick, Canada. Methods: A set of 602 plots, representing 12 stand types, were grouped into softwood (SW), mixedwood (MW), and hardwood (HW) categories. Net C change per year, including growth, recruitment of trees, and mortality, was calculated, and plots were categorized into three classes, of carbon sinks, sources, or neutral. Results: Over the period from 1987 to 2007, 68% of plots were C sinks, 25% were sources, and 7% were neutral. Balsam fir-spruce (Picea sp.) was the only stand type with negative mean C change at − 0.2 t C ha−1 yr−1. Long-term C projection using OSM (open stand model) determined that shade-tolerant hardwood and mixed stand types showed increases of 26–30% of total C over a 100-year simulation, whereas other stand types ranged between 7 and 21% increases. Conclusion: Balsam fir-dominated stands incur high mortality rates due to shorter longevity (stand decline) and high susceptibility to insect and wind disturbances, and therefore, HW and non-balsam fir-dominated MW should have priority in management for longer rotations to maximize C onsite.