Award Date

5-1-2012

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Committee Member

Scott R. Abella

Second Committee Member

Krystyna Stave

Third Committee Member

Michael Dwyer

Fourth Committee Member

Stanley Smith

Number of Pages

54

Abstract

This research explores several untested aspects of the seed bank characteristics of red brome (Bromus rubens), an invasive annual grass in southwestern United States arid lands. Red brome is a formidable competitor to native plant species, both annual and perennial alike, and produces many seeds that germinate easily. The stalks of red brome contribute continuous-cover fuel loads that facilitate wildfires destructive to mature native Mojave Desert plant communities. This makes it a priority species for land managers, particularly when dealing with recovery after fire.

This project addressed questions related to the longevity of red brome seeds in soil seed banks and the dynamics of seed densities after wildfires. After being experimentally buried, proportions of viable seeds in the soil were substantially reduced over time. Only six percent of seeds remained viable after one year of burial and 2.6 percent of seeds remained viable after two years of burial. Greater proportions of seeds lost their viability at greater burial depths. Soil seed bank density patterns of red brome were spatially variable across a 31-year time-since-fire chronosequence, and generally were not related to time-since-fire. However, some fires showed significant differences between microsites in burned and unburned areas. While fire disturbances did not necessarily promote greater seed densities of red brome over time in all burned areas, the youngest fire sites sampled in this study (six years after burning) exhibited little difference between burned and unburned areas. This study confirmed that, when red brome is a major component of above-ground vegetation, the species dominates the desert soil seed bank. Future research should consider longevity of seeds beyond two years, as well as comparing above-ground growth of red brome with seed densities observed in the greenhouse emergence study.

Keywords

Bromus rubens – Effect of fires on; Chronosequence; Desert wildfire; Invasive plants; Invasive species; Red brome; Seed banks; Seed longevity; Seeds – Dormancy; Soil seed banks; Southwest, New; United States – Mojave Desert; Wildfires

Disciplines

Desert Ecology | Environmental Health and Protection | Environmental Sciences | Plant Sciences | Weed Science

Language

English


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