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

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.

Permanent sample plot, Biomass, Species mix, Mortality, Net carbon change, Open stand model

Bashir, A., MacLean, D.A. & Hennigar, C.R. Annals of Forest Science (2019) 76: 35.

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Data availability
The data that support the findings of this study are available from the Department of Energy and Resource Development, New Brunswick, but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available. Data are however available from the authors upon reasonable request and with permission of the Department of Energy and Resource Development, New Brunswick.

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