Influence of growth-mortality balance and hardwood-softwood mix on stand and carbon dynamics of old stand types in New Brunswick

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University of New Brunswick
The influence of the balance between growth and mortality and hardwood-softwood mix on stand and carbon dynamics were studied in 602 old (mean age 84-108 years) permanent sample plots in New Brunswick, Canada. Plots represented 12 stand types, grouped into softwood (SW), mixedwood (MW), and hardwood (HW) categories. Tree mortality was variable and had the dominant influence on stand and carbon dynamics in each stand type, whereas increment of surviving trees and ingrowth were relatively constant among stand types. HW and other (non-fir-spruce (Abies-Picea)) SW stand types were stable, less vulnerable to spruce budworm (Choristoneura fumiferana (Clem.)) and windthrow than balsam fir (Abies balsamea (L.) Mill.) dominated stands, and thus well-suited for protection to develop into old growth forests and achieve long-term sequestration of on-site carbon. Results showed that the presence of balsam fir and spruce species was more important than broad stand type in determining stand dynamics, and indicated the carbon sequestration potential of older stands of different stand types. Stands dominated by balsam fir had the largest decline in volume with cumulative mortality of 118-134 m[superscript 3]ha[superscript -1] over 20 years due to short longevity and vulnerability to insect disturbance. Balsam fir–spruce was the only stand type with negative mean C change at -0.2 t C ha[superscript -1]yr[superscript -1] resulting in C release.