Potential and Economic Efficiency of Carbon Sequestration in Forest Biomass Through Silvicultural Management

Abstract This paper has two main objectives: First, to discuss in principle some vital methodological issues which have to be considered when analyzing how preferable measures in forestry are to decrease the atmospheric concentration of greenhouse gases (GHGs). Economic evaluation of the flow of carbon in and out of the atmosphere is discussed, related particularly to two important problems: (1) the determination of the utility of reducing the quantity of CO2 in the atmosphere at a given point in time; and (2) the intertemporal evaluation of a flow of atmospheric CO2 reductions. The marginal cost, measured as the change in net present value, is proposed as a proper measure for ranking of alternative projects. Secondly, a case study is reported. The case study is based on forest-level optimization with a model estimating carbon flows related to forest biomass growth and decay, linked to a long-range forest management planning (LFMP) model. Alternative stand treatment schedules are simulated, and the forest management problem is solved by linear programming in a model I type LFMP model for the county of Buskerud, with a forest area of 574,000 ha. The potential for increasing the net carbon sequestration related to timber production by changes in the forest management over a time period of 30 yr is studied. A total of 253 stand treatment schedules was calculated for the 40 stand types, allowing for the following stand treatment options, (1) continued growth, (2) release thinnings of young growth, (3) thinning, (4) fertilization, (5) dear felling, (6) clear felling with retention of seed trees, and (7) planting or natural regeneration depending on the felling regime. The study shows that there is a significant potential for increasing the present value of the flow of net CO2 fixations (NPVCO2) by changing the forest management on the productive forest area of Buskerud. Compared with the NPVCO2 obtained when the net present value of the timber cash flow (NPVNOK) for the area is maximized (BASE problem), an increase between 8.4%-17.9% in NPVCO2 can be obtained. The potential for increasing the NPVCO2 depends on the real rate of discount. The corresponding decrease in the NPVNOK lies between 8.1% and 14.9%. The results further indicate that a large proportion of the increase in NPVCO2 can be obtained by changes in forest management at a moderate marginal cost. If we assume that 80% of the maximum potential increase in NPVCO2 is obtained, this gives a yearly increase (30-yr annuity) in net CO2 fixation in the range from 145,000 to 250,000 tons (depending on the real rate of discount and assumptions about fertilization) by changing the management of the 574,000 ha of productive forestland in Buskerud, compared to the current forest management practice (BASE problem). Obtaining 80% of the maximum potential increase in NPVCO2 imposes a decrease in the NPVNOK in the range of 22% to 65% of the total potential difference in NPVNOK between the BASE problem and the NPVCO2 maximizing problem. The annual decrease (30-yr annuity) in NPVNOK corresponding to the 80% of the maximum potential NPVCO2 increase, is ranging between 7.6 and 25 million NOK. The results indicate that at a RRD of 4%, 5%, and 7% p.a., 80% of the increase in NPVCO2 can be reached at a marginal cost (shadow price) below 150 NOK (21/US$) per ton NPVCO2. Measured per ton C, the corresponding marginal cost is 551 NOK (79 US$) per ton C. For RRDs at 3% p.a. and 2% p.a., the marginal costs are significantly higher, but relaxing the NPVCO2 constraint to 60% of the total increase brings the marginal costs down and below half of this level (59 NOK or 8 US$ per ton NPVCO2) for 3% p.a. and to a comparable level (182 NOK or 26 US$ per ton NPVCO2) for 2% p.a. These results are related to changes in the management of the forested area in even-aged stands and do not take into account measures such as afforestation of marginal agricultural land or changes of tree species. Fertilization, avoiding release thinning in young growth, and changes in clear felling priorities were the most cost-efficient changes in stand treatment management in order to increase the net CO2 fixation. For. Sci. 40(3):429-451.