Evaluating Measure Selection and Timing for Carbon Sequestration, Stock Resilience, and Cross-Sector Trade-offs in Forested Regions: Insights from the KNOWING Project

Climate change requires transformative adaptation and mitigation measures across all sectors of society, to ensure the ambitions established under the Paris Agreement. However, the implementation of measures can also have wider-reaching trade-offs in other sectors or for competing objectives. These unintended effects require methods that can capture both the direct and ripple effects of interventions, in terms of co-benefits and trade-offs.

South-Westphalia is a majority forested (spruce-dominated) sub-region of North Rhine-Westphalia in western Germany, where societal actors are pursuing solutions to meet the climate mitigation goals linked to the Paris Agreement while ensuring those solutions would be compatible with future climate. Given its typicality compared to many European forests, successes in South-Westphalia could apply to other similar regions across Europe.

The research objective is to explore how different options for measure selection and timing in forested regions perform regarding carbon sequestration and future climate resilience while comparing their trade-offs for competing objectives in other sectors. This is accomplished using CLUMondo (a land system model) and a carbon model to simulate the impact of changes in forest composition and management strategies on surrounding land-uses and carbon sequestration. The land-use map outputs of these management scenarios are then evaluated per timestep for their changes in carbon stock, total sequestration compared to t₀, and sequestration increment. Furthermore, the effects on competing land-uses such as timbre from logging or yield from agriculture are evaluated to contextualise the effectiveness of measures/scenarios. The scenarios to be tested include a reference scenario (BAU), and alternative scenarios: afforestation with climate-adapted species; climate-adapted mixed forests; permanent forestry; and wind turbines. For each scenario, the speed and timing of measure implementation are tested for gradual, fast and instant implementation. The alternative scenarios aimed to reach carbon neutrality between the yearly emission from the local population (1.4 million people) of 2.95 Mt C (German emission per capita statistics multiplied by population) and the carbon sequestration increment per time-step by 2050.

Among the scenarios tested, afforestation with climate-adapted species showed good potential for sequestration, with a range of 2.06-2.7 Mt C sequestered per timestep in 2050 (depending on the speed of implementation), representing 69-92% of yearly emissions from South-Westphalia (3-4 times the reference scenario at 22%). However, the land-consuming nature of afforestation had large trade-offs for agricultural yields with a 77%  and 34% reduction in cropland and pasture areas respectively. Therefore, afforestation in smaller amounts would ideally be better combined with other less land-consuming measures such as wind turbines to meet carbon sequestration goals at a lesser trade-off cost. The size of the impact from the pace of measure implementation on the final results in 2050 highlights the importance of prompt policy-making to mitigate and adapt to climate change.