Semester

Spring

Date of Graduation

2020

Document Type

Thesis

Degree Type

MA

College

Eberly College of Arts and Sciences

Department

Geology and Geography

Committee Chair

Brenden E. McNeil

Committee Co-Chair

Nicolas Zegre

Committee Member

Trevor Harris

Abstract

The possibility of increased severity and frequency of drought conditions, as a result of global climate variability, greatly complicates our ability to forecast future forest functions such as productivity and carbon sequestration. Assessing how tree species vary in their response to drought can aid in predicting the impact on forest ecosystems as a whole. Throughfall exclusion (TfE) experiments are potentially useful tools to simulate realistic drought conditions within intact forest ecosystems. We employed a TfE experiment during the 2018 growing season within the WV Land Trust’s Elizabeth’s Woods Nature Preserve, near Morgantown, WV, to assess the leaf angle and leaf stomata responses of Quercus velutina and Acer saccharum trees to changes in water availability. I mounted time-lapse cameras within the forest crown of four experimental plots to track changes in leaf angle throughout the growing season. At the peak of the driest period of the summer, I also collected leaf samples for foliar isotopic concentrations analysis of leaf carbon (δ13C).

We consistently measured more vertical leaf angles within the Q. velutina plots compared to the A. saccharum plots. We found significantly more vertical mean leaf angles in the Q. velutina TfE treatment plot relative to the control plot at the beginning of the growing season, as soil moisture content declined, the vertical angles recorded in the control plot also increased. The δ13C analysis did not show a significant difference between Q. velutina treatment and control, suggesting an absence of stomatal control. A. saccharum had significantly higher values of δ13C in the treatment plot at the peak of the drought experiment, compared to the control and did not appear to adjust their leaf angle to account for the reduced water supply.

The leaf angle and leaf stomatal responses of these species are consistent with responses of other root and stem traits describing the position of each species on a theorized spectrum of hydrisity. In particular, the finding that anisohydric species use a mechanism of increasing leaf angle in response to low water availability has great implications for linking to remote sensing measurements and forecasts of forest functioning under the increasingly variable climatic conditions caused by global change.

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