Persistence potential of Great Basin high-elevation conifers under novel climates and disturbance regimes

Abstract

Forest persistence under global change will depend upon the capacity of species to persist in situ by tolerating water and temperature stress, rapidly adjust to novel conditions or migrate to track ecological niches. Contemporary climate change outpaces the adaptive capacity of long-lived, geographically isolated tree species, therefore differential regeneration success and proactive management will shape the future composition and distribution of forests. Focusing on the high-elevation pines of the Great Basin, I evaluate seedling success across a range of establishment conditions to assess the potential for ongoing natural regeneration and future reforestation interventions. Using observational and experimental approaches, I 1) characterized the natural regeneration niche for each species, 2) identified advantageous seedling traits and assessed evidence for local adaptation and plasticity while testing the utility of direct seeding, and 3) evaluated the ecophysiological limitations to seedling survival. My research shows species-specific differences in the regeneration niche and in seedling strategies for success that may lead to differential survival under novel conditions. I highlight the critical role that snowpack-driven soil moisture plays in natural regeneration, seedling emergence and function, and early seedling survival for all species. Climatic and edaphic specialization may limit regeneration success compared to more generalist strategies, however, plasticity may provide one mechanism for persistence in specialists. Drought-adapted traits varying by seed origin may be valuable for climate-informed reforestation, however, thresholds for mortality to extreme water and temperature stress were the same among species and populations. Our studies highlight the importance of natural regeneration for persistence, however, expected increases in water stress will reduce establishment opportunities and leave regenerating seedlings more vulnerable to drought-driven mortality.