Undergraduate Honors Theses

Thesis Defended

Fall 2017

Document Type


Type of Thesis

Departmental Honors


Ecology and Evolutionary Biology

First Advisor

Holly Barnard

Second Advisor

Barbara Demmig-Adams

Third Advisor

Thomas Veblen


In recent decades, a great deal of research has sought to define growing season and water source for ponderosa pine forests around the United States using stable carbon isotopic composition. These studies have focused primarily on developing models from multi-year datasets or environmental transects. We used stable carbon isotopic composition (∂13C) found in annual growth ring cellulose to examine seasonal precipitation’s importance to growth, and better understand how an individual extreme precipitation event might be utilized for growth in ponderosa pine trees in Colorado’s Front Range foothills. Spring precipitation, winter relative humidity, and summer relative humidity were all significantly correlated to ∂13C in latewood cellulose. Earlywood cellulose ∂13C was most correlated to combined winter and spring precipitation, and spring and summer relative humidity. The thousand year rain event that occurred in the study area in September 2013 did not manifest in isotopic values from 2013 growth rings, but the 2014 growth rings showed evidence of greater than expected water availability based on precipitation data. We suspect that water from the storm was stored at depth, and drawn upon by ponderosa pines through the 2014 growing season.