Honors Theses and Capstones

Date of Award

Spring 2022

Project Type

Senior Honors Thesis

College or School



Natural Resources and the Environment

Program or Major

Environmental Sciences

Degree Name

Bachelor of Science

First Advisor

Heidi Asbjornsen

Second Advisor

Michael Simmons


Global climate change is likely to affect northeastern U.S. forests by increasing the frequency and severity of drought events. Historically, droughts rarely occurred in this region, so native tree species are not well-adapted to extreme moisture stress. In the future, the changing climate will likely cause unprecedented levels of low water availability which may have implications on future forest composition. It is hypothesized that trees can respond to these environmental changes by altering their functional traits, also referred to as phenotypic plasticity; for example, by producing leaves with fewer and smaller stomata.

To determine the capacity to which oak trees adjust their functional leaf traits in response to water stress, stomatal size and density were measured in northern red oak (Quercus rubra), black oak (Q. velutina), and white oak (Q. alba)using leaves collected in 2020 and 2021 from the UNH Thompson Farm DroughtNet experiment. Imprints of the lower surface of each leaf were made with clear nail polish, mounted on slides, and examined under a light microscope. Images taken from these slides were then counted and measured using ImageJ software. Preliminary results show that both stomatal size and density values were lower in 2021 than 2020. No significant differences were found between drought and control treatments. Variation existed between individual trees of the same species and within different leaves of the same tree.