Diskontieren von Ökosystemleistungen: Effizienzsteigerung ohne Nebenwirkung?

Discounting is standard in economics to consider time preferences of people and account for future market changes. However, so far, discounting has mainly been applied to monetary flows and ignored for many ecosystem services. In multi-objective optimisation, selectively disregarding time preferences for some non-monetary services creates bias. Here, we study how discounting a range of ecosystem service indicators influences a public planner’s optimal land allocation. We used a robust multi-objective optimisation approach to model a mixed forestry-avocado farm portfolio in South Africa. The objectives for optimisation were the provisioning of various ecosystem services and disservices represented by four indicators: net present value, payback period, carbon sequestration, and fertiliser use. To account for time preferences concerning indicator flows, we applied specific discount rates to each ecosystem service indicator, depending on its character (non-monetary or monetary). We demonstrate that discounting reduces the standard deviations of the discounted sum of the indicators which leads to less diversified land use portfo-lios. To account for discount rate uncertainty, we introduced three indicator sets simultaneously, each using a different discount rate which was offsetting the effect of decreasing diversification.