Does climate change affect optimal planning solutions for multi-objective forest management?

摘要

The aim of this study was to: (i) demonstrate the combined use of a process-based growth model, a wood products model and a multi-objective optimization heuristic in the analysis of optimized management plans for a forest management unit (FMU) under changing climatic conditions, and (ii) to analyse the potential benefits of considering climate change in forest management planning. Specific questions addressed were: (a) how different climate scenarios affect optimized management plans, and (b) how management plans optimized for current climate perform under climate change scenarios. When analysing these questions, contrasting priorities for different management objectives within multipurpose forestry were considered. The case study was carried out within a management unit of 1451 hectares made up of a mosaic of Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and silver birch (Betula pendula) dominated stands in central Finland. Based on stand inventory data, the process-based growth model FinnFor was firstly used to simulate stand development over 100 years. Simulations were done utilizing the current climate and two transient climate change scenarios (ECHAM4 and HadCM2), employing six alternative management regimes (five thinning regimes and one unthinned management regime). The simulated timber harvests were inputted into a wood products model which estimated carbon sequestration in the products. Thereafter, a combined random and direct search optimization heuristic was employed to find, for each stand, a stand treatment programme (STP) that optimizes an additive utility function consisting of stand level and unit level components. A total of three management objective scenarios were analysed: timber production, carbon sequestration, and multi-objective management (timber, carbon, biodiversity). As a result, there were significant differences in the share of allocated STPs within the FMU between different management objective scenarios as well as between climate scenarios within each objective scenario. A generally observed pattern was that under climate change, regardless of objective scenarios, the share of some STPs increased compared to the results under current climate. Those STPs allowed a higher stand stocking over the rotation and later thinnings and/or final cutting compared to the currently recommended management. The relative increase in the utility of optimised plans due to climate change differed somewhat between the objective scenarios. For maxTP, the maximum increase was 16.8% (ECHAM4), while for maxCS it was 9.9% (HadCM2) and for MO 11.3% (ECHAM4). Depending on the management objectives and climate scenario, optimization contributed between 30% and 50% of that gain, the rest comes from increased production due to climate change. As a conclusion, the combined use of process models and multi-objective optimization appears a promising approach for multiple-use management planning under conditions of climate change.