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Long-term Fire Effects on Plant Succession and Exotic Weeds in Protected Area Sagebrush Steppe, John Day Fossil Beds National Monument, Oregon

ScholarsArchive at Oregon State University

Field Value
Title Long-term Fire Effects on Plant Succession and Exotic Weeds in Protected Area Sagebrush Steppe, John Day Fossil Beds National Monument, Oregon
Names Reed-Dustin, Claire Marie (creator)
Mata-Gonzalez, Ricardo (advisor)
Date Issued 2015-04-28 (iso8601)
Note Graduation date: 2015
Abstract The historical function of fire in sagebrush steppe has been altered by 19th century
overgrazing, active fire suppression, annual grass invasion and encroachment of woody
species. The significance of fire to these systems is known, but research on long-term fire
effects are limited. The Sheep Rock management unit of the John Day Fossil Beds
National Monument, Oregon offers an opportunity to study long-term (15 year) responses
of Artemisia tridentata ssp. wyomingensis (Wyoming big sagebrush) communities to fire.
Using generalized linear mixed models, this study examined responses of A. tridentata
ssp. wyomingensis, Bromus tectorum (cheatgrass), Gutierrezia sarothrae (broom
snakeweed), Poa secunda (Sandberg bluegrass), Pseudoroegneria spicata (bluebunch
wheatgrass) and Taeniatherum caput-medusae (medusahead), along gradients of
community type and topography through time post-fire. Community types were
differentiated between A. tridentata ssp. wyomingensis dominant plots (brush plots) and
Juniperus occidentalis (western juniper) dominant plots (forest plots). Cover of B.
tectorum was greatest in brush plots. Bromus tectorum cover increased dramatically 2
years post-burn. At 5 years post-burn cover of B. tectorum was 135% of pre-burn cover
in brush plots and 301% of pre-burn cover in forest plots. Analysis determined abundance
of T. caput-medusae was not enough pre-burn to analyze fire effects. Examination of
mean T. caput-medusae cover, in plots through time, suggests it is expanding within the
Sheep Rock management unit. Pseudoroegneria spicata is more abundant in forest plots
than in brush plots. In forest plots, P. spicata cover decreased by 49% 1 year post-burn,
but recovered by 5 years post-burn. In brush plots, cover of P. spicata declined, but not
significantly through time post-fire. On northern exposures recovery of P. spicata cover
occurred between 1 and 2 years post-burn, whereas on southern exposures recovery
occurred between 2 and 5 years post-burn. The cover of P. secunda did not show a
dramatic response to fire through time post-burn. Fire reduced A. tridentata ssp.
wyomingensis cover in brush plots by 99% and 100% on northern and southern
exposures, respectively. In forest plots, fire reduced A. tridentata ssp. wyomingensis
cover by 86% and 47% on northern and southern exposures, respectively. Similarly, A.
tridentata ssp. wyomingensis density in brush plots declined by 96% on both northern and
southern exposures 1 year post-fire. In forest plots fire reduced A. tridentata ssp.
wyomingensis density by 71% on northern exposures and 0% on southern exposures. The
cover and density of A. tridentata ssp. wyomingensis did not change significantly through
time after an initial decrease 1 year post-burn, except for density in forest plots, which
didn’t show significant change through time. Artemisia tridentata is a long-lived species
and therefore continuation of this study is required to gain a fuller perspective on its long
term response to fire. Cover of G. sarothrae declined by 92% in brush plots and by 73%
in forest plots. Gutierrezia sarothrae cover returned to pre-burn cover by 5 years post
burn in brush plots, but did not recover in forest plots. Topography was not identified as a
significant parameter for G. sarothrae cover in response to fire. Similarly to G. sarothrae
cover, G. sarothrae density decreased 1 year post-burn and recovered by 5 years post
burn in brush plots, but it did not recover in forest plots. In contrast to G. sarothrae
cover, topography was identified as a significant parameter for the response of G.
sarothrae density. We hypothesize south slopes favor G. sarothrae establishment, while
north slopes favor increased G. sarothrae size, which explains topographic significance
for density, but not for cover. Results of this study can be used by land managers to
consider species specific responses to fire in both the short and long-term. This
information is useful when developing plans for reintroducing fire into A. tridentata ssp.
wyomingensis systems or when developing post-wildfire management strategies.
Genre Thesis/Dissertation
Access Condition http://creativecommons.org/licenses/by-nc-nd/3.0/us/
Topic Fire Ecology
Identifier http://hdl.handle.net/1957/56016

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