Author (Your Name)

Rachel G. Daly, Colby College

Date of Award


Document Type

Honors Thesis (Open Access)


Colby College. Geology Dept.


Robert A. Gastaldo

Second Advisor

Bruce Rueger

Third Advisor

David Firmage


Stomatal frequencies of fossil-plant species are used to estimate past pCO2 levels based on the physiological functions of living taxa. Numerous studies have shown that there is an inverse relationship between pCO2 and stomatal frequency parameters. As levels of pCO2 increase, the Stomatal Density (SD) and Stomatal Index (SI) decrease. However, pCO2 is not the only factor affecting SD and SI values, which are a product of leaf growth and expansion. Stomatal characteristics differ between genera, and studies also have shown that SD and light intensity have a positive correlation. The present study hypothesizes that SD and SI are not influenced by a leaf's physical orientation relative to the sun during the growing season. Leaves of Northern Red Oak, Quercus rubra, were collected from trees on lake margins around six lakes in the Belgrade Lakes Region, central Maine, USA. Lakes oriented in NE/SW, NW/SE, and E/W directions allowed for sampling of trees exposed to varying light intensities throughout the growing-season day. The SD and SI of each tree were calculated and comparisons made between populations exposed to predominant morning or afternoon light intensities, and between populations on lakes of differing orientations. No comparisons show a statistically significant difference between populations under different orientations to growing-season sunlight. The data suggest that exposure to various sunlight regimes on opposite sides of lakes does not play a role in the stomatal response as reflected in SD and SI of plants during a growing season.


Red oak, Effect of light, Maine, Belgrade Lakes Region, Stomata