Large-Scale Forest Regeneration Dynamics Over Two Decades in Central Europe: A Representative Analysis

Forests provide essential ecosystem services, from carbon sequestration and biodiversity conservation to soil protection and socio-economic benefits. Understanding forest regeneration patterns is crucial for predicting future forest composition and ensuring the continued provision of these services. While long-term forest monitoring is well-established in Europe and in particular Switzerland through the National Forest Inventories (NFI) comprehensive analyses of regeneration trends across different forest communities remain limited. 

This study analyzes 20 years of regeneration data from the Swiss NFI's presence plots, spanning three inventory periods (NFI3: 2004-2006, NFI4: 2009-2017, NFI5: 2018-ongoing). We examine regeneration patterns across major forest communities, including beech, fir-beech, and fir-spruce forests, focusing on presence data for key tree species in two height categories: 40-130 cm and above 130 cm to 11.9 cm DBH. The presence plot methodology, implemented since NFI3, surveys 200 m² sampling areas, providing standardized data on species occurrence in the regeneration layer. 

Our analysis reveals significant temporal trends in species presence across different forest communities, identifying both increasing and decreasing patterns in regeneration success. Preliminary results for beech and fir-beech communities show distinct regeneration patterns: while most conifer species display stable or slightly increasing trends, we observe a notable expansion in deciduous tree presence, particularly beech and maple species. A concerning pattern emerges for European ash, showing a consistent decline across different forest communities. These findings provide crucial insights into the dynamics of Swiss forest regeneration and potential future forest composition. 

This comprehensive assessment of regeneration trends across Switzerland's diverse forest ecosystems offers valuable information for forest managers and policymakers, supporting evidence-based decisions in forest management and conservation strategies. The results contribute to our understanding of forest ecosystem resilience and adaptation potential in the face of environmental change.