|Abstract or Summary
- Anthropogenic land use alterations such as livestock grazing and fire
suppression have greatly altered sagebrush grasslands of the Great Basin,
facilitating invasion of exotic annuals, increases in woody species, and losses of
native species. Much of the current research surrounding wildland and prescribed
fire in sagebrush dominated ecosystems has focused on a persistent belief that fire
in sagebrush systems results in a loss of native flora and a trend toward dominance
by exotic annuals. Fire was historically the dominant disturbance throughout the
sagebrush steppe and the plant species that comprised these communities possess a
variety of adaptations facilitating survival to the fire regime. In order to restore
ecosystems, land managers will need to reintroduce natural ecosystem processes,
including natural disturbance processes.
To describe the response of these plant communities to fire, I examined the
plant community response, seedbank response, and reproductive and density
responses of three native bunchgrasses (Pseudoroegneria spicata, Achnatherum
therberianum, and Elymus elymoides) as well as one native forb (Calochortus
macrocarpus) following spring and fall prescribed fires at Lava Beds National
Monument. Fires were applied to three Artemisia tridentata ssp. vaseyana
(Mountain Big Sagebrush) plant communities with different land use and fire
histories. These communities were different in composition ranging from a
dominance of exotic annuals to dominance by native grasses, shrubs, and trees.
Little is known about how prescribed fire affects the soil seed bank in
sagebrush-dominated ecosystems. To address this, we quantified the emergence of
Bromus tectorum (cheatgrass) seedlings as well as emergence of seedlings of
functional groups (native forbs, bunchgrasses, and shrubs) in a seedbank
germination study. At the invasive dominated site (Gillems Camp), we found 91%
fewer B. tectorum seedlings germinated in spring burned sites than in controls
immediately following spring prescribed burns. However, soils collected one-year
following fire had 40% more B. tectorum germinants (8017 germinants/m [superscript 2]) than
unburned controls (5132 germinants/m [superscript 2]). Following fall burns at this site there
was a similar response, with a 56% immediate reduction in B. tectorum (as
compared to unburned control) and a 59% increase in B. tectorum and 58%
increase in exotic forb germinants one year following fires.
There was an increase in native forb germination following spring burns
(94%) and fall burns (45%) at a site dominated by native plants (Fleener
Chimneys). Native bunchgrass seed germination declined following spring fire in
sites dominated by sagebrush and native understory vegetation (79%), and in sites
where Juniperus occidentalis (western juniper) and other woody species
dominated (Merrill Caves) (71%).
In invasive-dominated sites (Gillems Camp), there was a decrease in B.
tectorum cover following both spring (81% decrease) and fall fires (82%
decrease), and little native vegetation composition change. Shrub cover, made up
predominantly of Chrysothamnus nauseosus, decreased following spring (95%
decrease) and fall (93% decrease) fires. At the sagebrush, native understory site
(Fleener Chimneys), there was a reduction in native bunchgrass cover (64%
decrease), and an increase in native forbs (168% increase) following spring burns,
with no changes following fall fires. At the juniper- woody dominated site (Merrill
Caves), fire treatments resulted in a decrease in woody plant cover, with no
immediate postfire differences seen in the herbaceous plant community.
Density of bunchgrass species (Pseudoroegneria spicata, Achnatherum
therberianum, Elymus elymoides) did not change following either spring or fall
prescribed fire treatments. Fire enhanced flowering was not seen in C.
macrocarpus following spring or fall burns at the native or juniper dominated
sites. There was increased reproductive effort in native bunchgrass species
following fires in all communities studied. Following spring fires at invasive
dominated sites, there was a 245% increase in reproductive culms of P. spicata.
Following fall fires in native dominated sites, we saw a 974% increase in
reproductive culms of P. spicata and a 184% increase in reproductive culms of A.
therberianum. Following fall fires at juniper-dominated sites, we saw in an
increase in reproductive culms of P. spicata (678% increase), A. thurberianum
(356% increase), and Elymus elymoides (209% increase). These results suggest
that implementing prescribed fire in order to restore the natural disturbance regime
in these fire-adapted ecosystems is beneficial to restoration and preservation of the