Scale-dependent effects of alternative forest management on structural connectivity in Sweden

Maintaining forest connectivity is vital for supporting the movement of forest-dwelling species and for sustaining the multiple ecosystem services and benefits forests provide to humanity. Forest Area Density (FAD) is the required metric for monitoring forest connectivity under the European Union Nature Restoration Regulation (EU NRR). FAD is a scale-dependent structural index, meaning that assessments of connectivity can change depending on the spatial scale of observation. Promoting biodiversity conservation under the EU NRR may involve a reduction in clear-cutting (CC) and the adoption of alternative, uneven-aged management strategies. Here, we simulate clear-cutting, and three alternative management strategies (AM1-AM3) in two contrasting Swedish regions. The simulations are designed to reflect the aggregated nature of harvesting blocks in CC management, and the more dispersed nature of harvesting blocks in alternative strategies. We calculate FAD relative to baseline (ΔFAD) at 11 observation scales (10–1,000 ha) and model the effects of management strategy, observation scale, and region. We show that, at fine observation scales, dispersed harvesting strategies consistently produce more negative ΔFAD than aggregated clearcuts. This reverses at observation scales of approximately 570-620 ha, as dispersed strategies result in gradually less negative ΔFAD. This is a mathematical property of the FAD metric itself, independent of the region. Our findings reveal an important tension between FAD as a structural connectivity metric and the ecological expectations of uneven-aged forestry.