Graduate Program

Biological Sciences

Degree Name

Master of Science (MS)

Semester of Degree Completion

Spring 2019

Thesis Director

Scott J. Meiners

Thesis Committee Member

X X

Thesis Committee Member

X X

Abstract

Mountains represent complex environment gradients which strongly affect local temperature regimes and rainfall. These changes in climate conditions drive a diversity of plant responses. As alpine environments are expected to change dramatically in response to climate change, understanding plant responses to environmental variation is critical in these environments. Although they are a critical component of alpine communities, the environmental responses of shrubs have been much less examined than trees, representing an important knowledge gap. Leaves, as the primary photosynthetic organs on plants, would be expected to respond strongly to local climate conditions. In this study, I documented how the leaf traits such as stomatal density (SD), stomatal length (SL), leaf area (LA) and length to width ratio (LWR) of the shrub community were associated with temperature (altitude) and precipitation. To do this, leaves were collected across 19 sites within the Sierra Nevada mountains among 12 shrub species including both deciduous and evergreen shrubs.

As expected, temperature decreased with increasing altitude, and there was a strong precipitation gradient, decreasing from west to east. I found strong variation across species in all four leaf traits, with shrubs species significantly associated with temperature. I expected plants of north temperate origin (deciduous) and southern origin (evergreen) to respond differently to environmental gradients. However, there were no systematic differences between evergreen and deciduous groups. Shrub species richness was negatively associated with temperature, reducing richness with elevation. Trait variation across the entire shrub community also responded to precipitation; traits SD and LWR showed decreasing variation with increasing levels of environmental stress.

Within species, LA was associated with temperature (altitude) and showed a decrease with elevation for 10 out of 12 shrub species. I found a general pattern of SD increasing with precipitation, except in a few species did not respond. Overall, the LA of deciduous shrubs increased with precipitation, while the evergreen species largely decreased with the altitude. There was no overall variation between evergreen and deciduous species, as was expected. This suggests that changes associated with climate change will not disproportionately fall on one functional group of shrubs. However, their environmental responsiveness suggests that these communities will be impacted by climate change over the long term.

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