Assessing the influence of deer browsing on forest ecosystem services with new stand-level optimization and agent-based models

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Deer browsing may strongly affect the development of forests with severe environmental consequences. While the existing research has intensely analyzed the bio-chemo-physical impact of deer browsing on the composition and growth of forest stands, a comprehensive assessment of the influence of deer browsing on the provisioning of ecosystem services (ES) is still lacking. Here we propose three interrelated research fields to fill this gap. 1) We suggest innovative stand-level multiple criteria optimization under uncertainty to derive ideal forest stands to be used as benchmarks that will optimally meet stakeholders’ preferences. The proposed innovations for enhancing such models include the treatment of ES occurring in the far future and the assessment of the robustness of ES provisioning. This first research field will consider timber provisioning, carbon sequestration, groundwater recharge, groundwater quality (for the example of nitrogen contamination), economic return and biodiversity as decision criteria (with dead wood as an indicator). 2) Based on the optimally composed benchmark forest stands we suggest simulation experiments to elucidate the impact of deer browsing. We propose implementing the benchmark forests in a forest landscape model and exposing them to deer browsing. For simulating the impact of deer, we will conceptualize an agent-based model. In such a model, young trees and deer are autonomous agents, where a framework for multi-agent research and simulation will support establishing interactions among such agents. Observations of the current project “BioWild” and existing literature will provide information to set up rules for the young trees’ response to browsing and the deer’s response to forest characteristics. 3) Assuming that intense deer browsing will form constraints for the optimal composition and management of a forest stand we suggest deriving shadow prices for the deer’s influence on the trees. These will encapsulate the costs for all ES included in the optimization of our benchmark forests. We expect that this research concept will allow a comprehensive assessment of the environmental impact of heavy deer browsing on trees.