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Alternative Title

Using response curves to inform carbon models

Publication Date


First Advisor

Danielle D. Ignace

Document Type

Honors Project

Degree Name

Bachelor of Arts


Biological Sciences


Plant, Ecology, Photosynthesis, Capacity, Tree, Carbon cycling, LI-COR


Forests store ~ 45% of terrestrial carbon and as human carbon emissions continue to increase the concentration of CO2

in our atmosphere which is known to cause large ramifications on every ecosystem. Global models used to predict climate change are not yet complete. Forest ecosystems have been considered the least understood ecosystem. Tree seedlings are discounted in carbon models because of their high mortality rate and low biomass relative to long-lived trees. However, seedlings contribute a significant portion of ecosystem carbon flux estimates due to their known high metabolic rates and huge abundance in forest systems. I asked: (1) How do dominant seedling species differ in their photosynthetic capacity? and (2) How do seedlings differ compared to older trees? I measured the photosynthetic capacity of seedlings by collecting CO2 and light response curves. These measurements were taken at Harvard Forest (Petersham, MA) with four species: red maple (Acer rubrum), red oak (Quercus rubra), white pine (Pinus strobus), and eastern hemlock (Tsuga canadensis). To find photosynthetic parameters Sharkey and Ye Excel models were run on the response curve data. Leaf tissue samples were harvested from all individuals for analysis of carbon and nitrogen content, and stables isotopes of carbon. The results showed significant differences in the photosynthetic capacities of seedlings and mature trees, with white pine species having the highest photosynthetic capacity and eastern hemlock having the lowest. These results highlight the need to include seedlings in forest carbon models, as they can shockingly have a larger photosynthetic capacity than some adult species of trees. In order to correctly inform global carbon models and improve their accuracy we must consider all organisms large and small.


2020 Alonwyn L. Clauser. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.




53 pages : color graphs. Includes bibliographical references (pages 44-52)