Searching for Sustainable National Forest Harvest levels through Interactive Multiobjective Optimization

In Finland, linear optimization has been used to search for sustainable national harvest levels for over 30 years-commonly maximizing net present value from forests county by county, while ensuring sustainablility of wood production by requiring nondecreasing harvest levels over time. However, this approach does not help policymakers understand how the selected harvest level is reached and what affects the result. Moreover, optimizing per county may lead to an inefficient solution, as the counties serve as constraints. National-level interactive planning is a better approach, but such interactive optimization is compute-intensive. We present an interactive multiobjective optimization approach applying the NAUTILUS Navigator method. It is based on pre-calculated optimal solutions and gradual improvements from the nadir (the worst solution). We apply the approach in a novel way: starting with a sparse representation of optimal solutions and generating a denser representation in the area of interest, saving computational resources. The problem formulation is also improved during the solution process. Moreover, the interactive approach advises decision makers on the consequences of the selected solution better than a few pre-selected scenarios. The decision maker can direct the solution process and find preferred solutions. The results also show improvement in solutions when the county-level constraints are removed.