Since European American settlement of the Intermountain Region,
dramatic changes in vegetation composition and structure have occurred in the
sagebrush steppe ecosystem. Western juniper (Juniperus occidentalis spp.
occidentalis Vasek), although indigenous to the Intermountain Region, has
increased since the late 1800s. Considerable work has been done documenting
juniper woodland expansion in the Intermountain West, however, little is known
about the environmental variables that influence rates of tree establishment and
structural attributes of woodlands across landscapes. Most studies of western
juniper have addressed site-specific questions at limited spatial scales.
Consequently, there is a lack of research on broader scale patterns of woodland
development occurring across heterogeneous landscapes. In addition, changes in
the amount, composition, and structure of fuels during the transition from open
sagebrush steppe communities to closed juniper woodlands have profound
influences on the size, intensity, frequency, and behavior of fire. However, limited
data exist quantifying changes in fuels during this transition, thus, consequences to
fire behavior have been difficult to predict. The major impetus for the study was
to determine the influence of environmental variables on rates and structural
attributes of woodland development and associated changes in fuel loading
characteristics during the transition from sagebrush steppe communities to closed
juniper woodlands in the High Desert and Humboldt ecological provinces. The
proportion of trees greater than 150 years old relative to trees less than 150 years
suggest western juniper has greatly expanded in the Owyhee Mountains and on
Steens Mountain since settlement of the areas. Ninety-five percent of the trees
established after the 1850s. As evidenced by the presence of western juniper in
96% of plots sampled in this study, juniper is able to encroach upon a variety of
plant alliances and under a broad range of environmental conditions over diverse
landscapes. Although it appears the occurrence of western juniper within the
woodland belt is not spatially limited by environmental or vegetative conditions,
stand structural and fuel loading characteristics do vary considerably across
heterogeneous landscapes. Total juniper density, density of dominant trees
comprising the primary canopy, and certain live and dead fuels biomass very
substantially with site potential. Spatial variation in stand structure and fuels may
have significant implications to management of juniper at the landscape scale. / Graduation date: 2005
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29440 |
| Date | 22 February 2005 |
| Creators | Johnson, Dustin D. |
| Contributors | Miller, Richard F. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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