Modeling of forest harvest scheduling and terrestrial carbon sequestration.

摘要

It has generally been agreed that forests sequester atmospheric carbon and thus contribute to mitigating anthropogenic emissions in a cost effective manner compared to other available carbon sequestration techniques. With increasing concerns on global greenhouse gases and emerging carbon markets, additional carbon sequestered as a result of sustainable forest management activities can be of significant benefits for forest landowners. Harvesting, an important forest management activity, plays a crucial role in determining the forest's ability in sequestrating carbon. Harvesting modifies the forest carbon sequestration potential depending on time of harvest, age of stands, species composition, and types of harvest. The allocation of forest harvest units (tracts over time and space) come under the broader domain of tactical forest harvest scheduling. A need to analyze the role of different harvesting strategies was found essential, as such analysis will help design harvest schedules for a given forest aimed at enhancing carbon sequestration.In order to study the forest harvest strategies, a computer-based forest planning system was developed for generating and visualizing a spatio-temporal forest harvesting plan for different management objectives. The system adapted a two staged block generation approach using maximal feasible cliques to formulate spatial, temporal and related restrictions. The linear programming based solver was employed to provide the solution to the spatial problem which resides at the backend along with a relational database which stores different forest, operation and management related data. The system runs with minimal information required from the user, such as management objective selected, time frame of the planning horizon and periods, and other management restrictions as binary inputs. All the modeling processes and complexities were automated in the system using tested algorithms which are often the major challenges in planning processes. This integrated system simplifies the planning processes and ensures that the generated spatial plan meets the long term objectives of management. The developed system was used to optimize different harvest schedules. The generated schedules had different objective functions ranging from maximization of timber production maximization of timber production and stand carbon stock to maximization of only carbon stock under clearcut and selection cut methods applicable for both long and short rotations.Altogether, 19 different harvest schedules were developed to evaluate forest carbon sequestration. Higher carbon sequestration rates can be achieved by maximizing current harvested volume and future carbon stock when stands recover from the disturbance effects of harvesting in both selection cut and clearcut methods without undermining the potential benefits from harvested timber. The recovery period option explored is a new approach in generating harvest schedules for enhanced carbon sequestration combined with achievable timber benefits. The optimized harvest scheduling was then implemented for the entire state for possible carbon enhancement options. Carbon sequestration in the four terrestrial ecosystem components including forests, agricultural lands, abandoned mine lands and harvested wood products were modeled using a system modeling approach. This model tracks carbon stock and flow in different components over time. The carbon stored in harvested forest product pools were estimated using existing, as well as potential, growth-to-removal ratios followed by decay functions applicable for different forest product types.Several potential enhancement options in the terrestrial carbon sequestration were obtained by generating management scenarios including afforestation activities in marginal agricultural lands and abandoned mine lands. The research found that current terrestrial ecosystem components in West Virginia sequester atmospheric carbon at the rate of 4.99 million tons of carbon per year with a possibility of achieving an enhanced sequestration of 7.62 million tons of carbon per year when all the available options are implemented. The study also concluded that sustainable terrestrial ecosystem management can provide higher carbon sequestration rates at a lower cost than available alternative options. It also provides a path to utilize this green energy to substitute for fossil fuels to meet the long-term objectives of emission control in the state.