EAGER: Quantifying the relative importance of reproduction in forest dynamics under historical and future climate change

Environmental change will alter forest dynamics and species composition. Tree reproduction and recruitment are critical processes for tree populations and ultimately, determine the future species composition of forests. Even though tree reproduction is sensitive to climate, the relative importance of this process for forest dynamics is unclear, especially compared to anticipated climate-change effects on tree growth and mortality.

Seed production and seedling survival are also determined by individual and stand level properties. For example, seedling survival is affected by light availability. Increasing mortality due to climate change will alter the amount of light hitting the forest floor, and affect seedling survival.

Seed production is also affected by size (i.e., larger individuals tend to produce more seed). If tree growth responds positively to climate change, this could indirectly cause an increase in seed production. Thus, to capture all these direct and indirect effects, the project will update a dynamic vegetation model (DVM) to explicitly simulate reproduction as a function of weather and stand structure.

Including tree regeneration dynamics in process-based vegetation models is a major research gap and a critical step for accurately projecting forest responses to climate change. The project broader impacts include (1) training for students in computer programming, database management, data analysis, and communicating science, and (2) outreach activities to broaden participation of women in computer science.

Using forests located in the Pacific Northwest (PNW) as a case study, the project will quantify the relationships for seed production (as a function of weather and size) and seedling survival (as a function of weather and stand structure), for common tree species in the PNW. These relationships will be incorporated into a forest model, that already includes species-specific simulations of growth, competition and mortality as a function of the environment.

The updated model will be used to simulate forest stands located in the PNW under historical climate and various climate change scenarios. By comparing model versions, the research will be able to quantify the relative role of reproduction on forest dynamics and species turnover and identify species vulnerable to climate 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.