Date of Award


Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Applied Ecology (MS)

Administrative Home Department

College of Forest Resources and Environmental Science

Advisor 1

Molly Cavaleri

Committee Member 1

Robert Froese

Committee Member 2

Noel Urban


Rising mean annual temperatures due to climate change have intensified the need to understand the effects of warming on plant physiological processes. Forest photosynthesis is the most important pathways of terrestrial carbon sequestration, yet continued warming could reduce this important carbon sink. Photosynthesis is highly sensitive to temperature and begins to decline after an optimum temperature (Topt) is reached, leading to reduced carbon uptake. To date, logistical difficulties have limited our ability to test photosynthetic responses to sustained warming in mature forest canopies. In order to understand how elevated temperatures will affect forest ecosystems, we need to be able to test acclimation responses in-situ. The two primary aims of this thesis were: (1) to test and describe a leaf-level warming device that can be implemented within a forest canopy, and (2) to investigate the responses of two northern hardwood species to experimental canopy warming. We successfully developed a leaf-level warming device that warmed leaves 3.02 ± 1.86 °C above control leaves within mature forest tree crowns. To examine photosynthetic acclimation response, we heated understory and canopy leaves of Acer saccharum and Tilia americana for one week at < 2 meters, 6.25 m, and 12.5 m heights. We measured the photosynthetic, stomatal conductance, and leaf trait response to temperature, as well as how responses differed throughout a vertical canopy gradient. We found no evidence of thermal acclimation in plant gas exchange or leaf traits for either species at any height. However, we did find evidence of slight photosynthetic decline, indicating possible damage to photosynthetic apparatus. Topt was consistently higher than daily maximum temperatures for T. americana leaves, while Topt was at or below daily maximum temperatures for A. saccharum. This suggests that T. americana is less likely to experience photosynthetic decline under climate warming than A. saccharum. Future studies should investigate the effects of longer-term warming on northern hardwood canopies.