Collaborative Research: Continent-wide forest recruitment change: the interactions between climate, habitat, and consumers

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The sustainability of North American forests depends on seed production by trees as well as seedlings that must establish for the next generation of trees. For most of North America, neither the amounts of seed that are produced, nor how much of that seed survives to become adult trees is known. Population spread beyond current frontiers will be governed by seed production of trees (fecundity), germination, and seedling survival—the capacity of trees to produce seed and disperse it to the habitats where populations can survive in the future. Planning for environmental change impacts requires this knowledge to anticipate tree species migrations and its impacts on the birds and mammals that depend on forests for habitat and food. Understanding these forest recruitment responses requires a methodological shift from the current method of monitoring of seeds, seedlings, and consumers on small plots to extensive sampling methods that can be implemented at biogeographic scales. This study combines continental scale tree fecundity estimates with a new generation of monitoring and synthesis methods for integrating tree fecundity, seedling success, and its impacts on animal consumers. This research will quantify current trends across the continent, the changes in forests that are happening now, and the habitat changes that are causing them. Development of a biogeographic network of tree fecundity and recruitment will provide the monitoring platform needed for science and management of future forests. Broader impacts will focus on stakeholder integration, including conservation and management planning, information transfer to stakeholders in federal and state agencies, and citizen science outreach. Products of the study will have immediate application to forest regeneration practices in the coming decades. Agency and NGO stakeholders will advise and disseminate products of the study. New analytical tools will identify where tree recruitment is limited in North America, its rate of change, and what’s causing it. The project focuses on three recruitment stages, seed supply (seed mass per tree abundance), seedling establishment (seedlings per seed mass), and recruitment rate (advanced regeneration per seedling). Each recruitment stage will be linked to climate and habitat variables and to the vertebrate consumers of seeds, fruits, and nuts. Extensive gradient sampling (EGS) is a new approach to estimate the key demographic rates that are relevant at the scale of habitats or plant communities, while combining it with traditional data already available from the meter-scale intensive monitoring sampling (IMS). The project will include data collection based on this new approach, (EGS) of fecundity, tree recruitment, and vertebrates distributed across climate and habitats. Predictive vertebrate modeling (PVM) of activity based on camera traps (snapshot USA, NEON, and this study), live trapping (NEON sites) and bird point counts (BBS, NEON, and eBird) across North America will be conducted by the research team. By understanding tree recruitment and the vertebrates that depend on them, this study will i) identify the species that are limited by recruitment, including the habitats and stages where limitation occurs, ii) quantify the relationship with vertebrate activity, and iii) evaluate predictive distributions of change that account for climate-vertebrate interactions fitted to data. Quantifying tree fecundity and animal-consumer relationships at biogeographic scales will provide a foundation for the next generation of efforts to understand food web implications of environmental change.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.