Restoring native forests from Pinus radiata plantations: natural regeneration of native tree species in response to different harvesting treatments in central Chile

The natural forests of south-central Chile are known as world biodiversity hotspot. Due to increasing societal demands and certification commitments, a vast extension of these forests that was replaced by commercial exotic tree plantations is now to be restored. Given the magnitude of the area involved, large-scale approaches based on natural regeneration require consideration. However, experimental evidence for this approach to restoration is lacking in different regions. We conducted a large-scale replicated experiment to evaluate the response of natural regeneration of native tree species to different harvesting treatments (clearcut, strip-cutting, and unharvested control) in 20-year-old Pinus radiata plantations. For 2 years, we monitored variations in (1) regeneration basal area (dRBA), (2) maximum sapling height (dMH), (3) frequency of free-growing regeneration (dFGR), and (4) diversity of regenerating tree species. The harvesting treatment had significant effects on dRBA, dMH, and dFGR. The clearcuts showed the highest values of dRBA and dFGR of native species, but also, the highest dRBA of P. radiata regeneration. The strip-cuttings showed the highest dMH of native species and the highest values of richness, Shannon, and Simpson diversity. Our results suggest that both clearcuts and strip-cuttings facilitate natural regeneration. Although clearcuts may allow higher rates of natural regeneration establishment than strip-cuttings, they require periodic control of P. radiata regeneration to prevent suppression of established native regeneration. Strip-cuttings may require fewer management interventions and allow for higher initial species diversity, although with a potentially longer establishment period and higher risk of damage from residual P. radiata trees experiencing wind throw.