The effects of forest management on carbon storage in uneven-aged forests and wood products

Background/Question/Methods

Forests play an important role in the global carbon cycle and hence the mitigation of climate changes.  Harvesting reduces carbon storage in forests, but also increases the amount of carbon stored in wood products and landfills. Harvesting may also increase forest productivity, thereby accelerating the accumulation of carbon in wood products and further offsetting any reduction in forest carbon storage.  Thus, the net effect of harvesting depends not only on the change in forest carbon pools, but also on the rate throughput. Here we develop a model to simulate carbon dynamics in uneven-aged hardwood forests of central Ontario, including the growth and mortality of trees, the decay of dead organic matter pools in soils, the fate of wood products, and decay of wood matters in landfill. Selection silviculture was simulated using the BDq method, including residual basal area after each harvest (B), maximum diameter at breast height (D), the ratio of the stem densities between neighboring DBH bins (q), and harvest interval.

Results/Conclusions

The total carbon storage in forests and wood products would increase to some extent with the increment of harvest. There existed a turning point (yearly mean harvest at about 2.6 tonne ha^-1), however, after which the total carbon decreased with the intensified harvest. Moreover, forest structures (represented by BDq scenarios) also affect the carbon stock and timber production. Both the timber production and total carbon stock increase along with decrease of maximum DBH and harvest interval. The age structure in the uneven-aged forest (represented by q-ratio) has more complicated effects on harvest and total carbon stock. With the DBH bin size defined as 2 cm, the total carbon stock in forests and wood products reach the peak when q-ratio was 1.12; whereas the largest timber production could be reached when q-ratio ≥ 1.25. Residual basal area after harvest had conflict effect to timber production and carbon storage. Lower residual basal area would increase the harvested volume but decrease total carbon stock. Thus, the optimal management regime, regarding the carbon stock and timber production, would be to decrease the portion of old trees (reduce maximum DBH), shorten harvest interval, and maintain the age structure at a certain level (i.e. q-ratio between 1.12-1.25).