Forest landscape restoration, such as tree planting, is gaining significant attention, especially in the context of carbon sequestration and biodiversity conservation, within the framework of Nature-based Solutions. Here there is an essential need to recognize that naturally functioning forests provide diverse ecosystem services. To effectively restore natural forests in degraded areas, several restoration approaches have been studied, including tree planting (active restoration), natural regeneration (passive restoration), and human interventions to promote natural regeneration (assisted natural regeneration). There is an increasing body of evidence that suggests the most cost-effective approach to restoring forests at a landscape scale is through accelerating the process of natural regeneration (if restoration time is not a constraint). However, the potential of simple plantations mainly composed of single tree species or alien trees, which are one of the major schemes for reforestation activities worldwide, as a tool for fostering natural regeneration has not been thoroughly explored. As both natural regeneration and tree planting can complement each other, it is crucial to evaluate the role of plantations in assisted natural regeneration.

This presentation focuses on the potential role of monoculture plantations in supporting natural forest restoration. The study was conducted in Shiretoko National Park, Japan, using remote sensing, vegetation inventory, and simulation modeling to assess whether monoculture plantations support or hinder the establishment of naturally regenerating forests in the short and long term. The results indicate that monoculture plantations of larch, though it is an alien species, can have a positive effect on natural forest restoration. Specifically, they can protect native tree species from predominant winds and promote the regeneration of native tree saplings and seedlings, even under high herbivory pressure. This would be because of their rapid growth, cold tolerance, and leaf phenology, which could help foster the regeneration of native tree species. We note, however, the restoration potential of plantations to recover natural forests differed between plantations of light-demanding and short-lived species and those of shade-tolerant and long-lived species. In sum, the study highlights the importance of evaluating the restoration potential of plantations, including planted tree species, planting densities, and species richness, as well as species-specific traits. While the study does not advocate for the proactive establishment of simple plantations, it concludes that managers need to be aware of the context-dependency of plantations of single species or alien species to make restoration more effective, especially in areas where they have already been established.