Award Date

5-1-2021

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Life Sciences

First Committee Member

Matthew Petrie

Second Committee Member

Dale Devitt

Third Committee Member

Scott Abella

Fourth Committee Member

Bethany Coulthard

Number of Pages

98

Abstract

Trees in semiarid forests and woodlands of the western United States need soil moisture to transpire and function. Juvenile trees are especially vulnerable during periods of low soil moisture as their rooting zones are smaller and shallower than those of adult trees. This thesis focuses on two soil moisture-driven aspects of semiarid forests that may be modified by climate change: seasonal soil moisture patterns and juvenile tree survival.

In chapter 1, I investigated the influence of precipitation on soil moisture across seasons, elevations, soil layers, and periods of low and high precipitation. I developed time-varying definitions of winter (snow accumulation), spring (moisture recharge), and summer (moisture deficit) that could be applied broadly to sites across the southwestern United States. Higher elevation sites (> 2800 m) displayed similar patterns of greater winter precipitation, longer springs, and shorter summers compared to lower elevation sites (< 2500 m). Across season influence of soil moisture (e.g. an earlier season’s similarity to subsequent seasons) was high when the first season experienced above- or below-average precipitation and the next season experienced average precipitation, highlighting an important connection through time initiated by wet or dry conditions. Soil moisture in the summer season of moisture deficit relied entirely on precipitation events for recharge.

In chapter 2, I investigated the effect of a single season of moisture deficit on ponderosa pine juvenile survival and functioning. Juvenile ponderosa pine experimentally treated with small rainfall events for a moderate dry period of 45 days experienced widespread loss of function and mortality regardless of microclimate and total rainfall. A single season of moisture deficit has the potential to severely limit regeneration success in semiarid forests.

My research identifies broad similarities in precipitation-soil moisture relationships across the southwestern United States, the extent to which average moisture conditions are a barrier to semiarid forest regeneration, and how these relationships between precipitation, soil moisture, and juvenile tree survival may be altered in a changing climate. Overall, my thesis highlights the climate change-influenced conditions that may negatively impact semiarid forest persistence in the future.

Keywords

Climate; Juvenile tree; Precipitation; Soil moisture

Disciplines

Environmental Sciences | Terrestrial and Aquatic Ecology

File Format

pdf

File Size

2500 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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