Response of natural tree regeneration to climate adaptation treatments in Pinus resinosa-dominated forests

Uncertainty and emerging threats associated with climate change necessitate the development of new approaches for managing forest ecosystems. To address this need the Adaptive Silviculture for Climate Change (ASCC) Network was established to examine the efficacy of three climate adaptation strategies in important forest types across North America: 1) resistance to change by increasing overstory tree health through reduced inter-tree competition, 2) resilience by creating conditions that allow change within the natural range of variability while encouraging greater abundance of native species considered suitable for projected future climate, and 3) transition which involves actively facilitating systems to have a more adaptive response. The present study focused on the influence of Adaptive Silviculture for Climate Change treatments on natural regeneration in a Pinus resinosa Ait. (red pine)-dominated forest in northern Minnesota, USA. We aimed to answer the following research questions: 1) How do different climate adaptation strategies (resistance, resilience, and transition) influence natural regeneration relative to passive management? 2) Do impacts on the understory woody community, including trees and shrubs, differ among treatments in terms of abundance, composition, and diversity? Naturally regenerated trees and shrubs were sampled during the 5th growing season following Adaptive Silviculture for Climate Change treatment implementation (May-August 2019). The species composition of naturally regenerated trees differed among treatments as did adaptability, quantified as a composite index that integrated disturbance response and life history traits. The transition treatment resulted in greater capacity for adaptation to future conditions in the newly regenerated cohort. All treatments increased tree species diversity and richness relative to passive management, but the greatest woody species diversity occurred in the resilience treatment. This suggests a trade-off between maximizing woody species diversity (greatest in the resilience treatment) and adaptability (greatest in transition treatment). Overall, these results affirm the potential for using silviculture to increase tree diversity and adaptability through natural regeneration in anticipation of threats posed by changing climate in a major forest type, with results serving as a model for expectations in similar ecosystems.