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Cheatgrass Die-Offs: A Unique Restoration Opportunity in Northern Nevada


Abstract and Figures

• The phenomenon of cheatgrass die-off is a common and naturally occurring stand failure that can eliminate the presence of this annual grass for a year or more, affecting tens to hundreds of thousands of acres in some years. • We designed a study to determine if the temporary lack of cheatgrass caused by die-offs is a restoration opportunity. We seeded native perennial species at three die-offs in the Winnemucca, Nevada, area. • Native grass establishment in die-offs was almost three times higher in the first season at all sites, relative to adjacent areas without die-off. Establishment was five times higher in the die-off at two sites in the second season, and plants produced dramatically more culms in the die-off at the third site in the third season. • Increasing seed rates led to more seedlings establishing in both die-offs and controls, with the strongest effect in the second season. • We suggest that landowners and managers consider targeting die-offs as efficient locations to focus native restoration efforts and that restoration practitioners should consider increasing seeding rates to maximize success.
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Cheatgrass Die-Offs:
A Unique Restoration Opportunity in
Northern Nevada
By Owen W. Baughman, Robert Burton, Mark Williams, Peter J. Weisberg,
Thomas E. Dilts, and Elizabeth A. Leger
On the Ground
The phenomenon of cheatgrass die-off is a common
and naturally occurring stand failure that can
eliminate the presence of this annual grass for a
year or more, affecting tens of thousands of
hectares in some years.
We designed a study to determine if the temporary
lack of cheatgrass caused by die-offs is a restoration
opportunity. We seeded native perennial species at
three die-offs in the Winnemucca, Nevada, area.
Native grass establishment in die-offs was almost
three times higher in the first season at all sites,
relative to adjacent areas without die-off. Establishment
was five times higher in the die-off at two sites in the
second season, and plants produced dramatically more
culms in the die-off at the third site in the third season.
Increasing seed rates led to more seedlings establishing
in both die-offs and controls, with the strongest effect in
the second season.
We suggest that landowners and managers consider
targeting die-offs as efficient locations to focus native
restoration efforts and that restoration practitioners should
consider increasing seeding rates to maximize success.
Keywords: Great Basin, revegetation,
Bromus tectorum, cheatgrass, die-off, restoration.
Rangelands xx(x):1—9
doi 10.1016/j.rala.2017.09.001
©2017 The Society for Range Management.
Cheatgrass (Bromus tectorum) is one of North Americas
most ecologically significant invasive species, growing in
impressively dense near-monocultures across many
parts of the West. Because it is highly competitive, it
is a severe barrier to the survival of seedlings of perennial plants,
especially in sagebrush steppe communities.
Cheatgrass die-off,
or stand replacement failure, is a naturally occurring phenomenon in
which a seemingly healthy stand of cheatgrass fails to replace itself.
Die-offs result in the complete elimination of cheatgrass at a site for
oneormoregrowingseasons(Fig. 1). The cause of this
phenomenon is under investigation
and likely involves one or
more pathogens reaching epidemic levels under certain conditions.
Only actively growing seeds are affected, so dormant cheatgrass
seeds remain in the soil during and after the die-off, often resulting
in a return to cheatgrass dominance within a year or two.
Because these die-offs occur in remote areas, it can be
difficult to understand how common they are. However, their
distinct color and patterns make them perfect for detection
with aerial or satellite imagery. In a recent remote sensing
study focused on a highly invaded region of north-central
Nevada centered on Winnemucca, we found that over
100,000 hectares of die-off have occurred over the last 31
years (Fig. 2).
Throughout the 1.7 million hectare study
area, some years produced no die-off, around one-third of
years produced 4,800 ha or more, and three years each
produced over 40,000 ha of die-off. This study also found
that certain areas (totaling around 15,000 ha) are hotspots
that have experienced die-off four to nine times during the
31-year period. Cheatgrass die-off has also been observed in
other arid shrublands in the west, including Washington,
Utah, Idaho, and Oregon (O. Baughman, personal observa-
tion), and areas of unexpectedly low productivity of
cheatgrass that could be die-offs have been remotely sensed
throughout much of the northern Great Basin.
die-offs can cause problems for land users because these areas
may experience increased soil erosion, invasions of other weed
species, and a sudden loss of spring forage. However, die-offs
may also represent excellent opportunities for establishing
seedlings of perennial plants, which is what we investigate here.
Can Die-offs Increase Restoration Success in
Areas Where There Are Few Options?
Compared with other forms of temporary cheatgrass control,
such as herbicide or targeted grazing, the die-off phenomenon is
not costly or labor intensive, but it still provides conditions that
may help native plants grow. For example, soil moisture,
plant-available nitrogen, and other essential nutrients are higher
2017 1
in recent die-off soils than soils of nearby areas that did not
experience die-off.
We conducted a precision seeding study
to test how die-offs affected perennial grass seeds at a die-off in
Pershing County, Nevada, in 2012.
We planted Sandberg
bluegrass (Poa secunda) and bottlebrush squirreltail (Elymus
elymoides) into a recent die-off as well as an adjacent intact
cheatgrass stand (control). The die-off supported more
bluegrass and squirreltail through 2 years of monitoring, and
seedlings in the die-off had significantly greater growth and
vigor late in the growing season than those in the control. These
findings were promising, especially considering the competitive
pressure exerted on these native seedlings by cheatgrass, which
was common and returning to dominance during the study.
These promising results suggested that cheatgrass die-offs
can increase restoration success in highly invaded areas, but
our seeding was limited to only one site and two native species
and used a nontypical method of hand-seeding. Therefore,
researchers at the University of Nevada, Reno and managers at
the Bureau of Land Management initiated this follow-up
study to determine if similar results would be found across
multiple die-off sites, seeding a greater diversity of native
species and using typical drill-seeding methods. Additionally,
we were interested in whether simply increasing the seeding
rate could improve native establishment. The questions of our
study were as follows:
1. Do recent cheatgrass die-offs support higher establishment of
native grass, forb, and shrub seeds after mechanical seeding?
2. Do higher seed rates result in higher establishment of
native grass, forb, and shrub seeds, in or out of cheatgrass
Sites, Seeding, and Monitoring
Three sites that contained an area of complete stand failure
(die-off) as well as an immediately adjacent stand of cheatgrass
(control) were selected for seeding (Fig. 1). Buena Vista and
Paradise were formerly dominated by Wyoming sagebrush
(Artemisia tridentata ssp. wyomingensis), while Four Corners was
likely dominated by a mix of Wyoming sagebrush and salt desert
scrub species. At the time of seeding, all sites had been dominated
by cheatgrass for over a decade, with a mix of other exotic and
native species existing at much lower levels. Die-off and control
Figure 1. Many cheatgrass die-offs are so devoid of vegetation that they can be seen from far away, as well as in satellite imagery. Photos are satellite
(top images) and ground-level views (bottom images) of the three sites used in this experiment. Satellite images show the die-off boundary
(dashed outline) and experimental fields in the die-off (light boxes) and control (dark boxes), all of which were fenced soon after seeding. In the ground-level
views, the characteristic gray litter of a recent die-off in the foreground contrasts with the light yellow of dried cheatgrass in the background. Note that the
date (lower left of each panel) and scale (upper right of each satellite panel) vary.
fields were less than 400 m from one another and were each
enclosed with barbed wire fences constructed after seeding.
An approximately 0.2 ha area within each die-off and
control area at each site was designated as the study field, and
Figure 2. In this region of Northern Nevada, over 100,000 hectares of cheatgrass-infested rangelands have experienced cheatgrass die-off over the past
31 years. This map summarizes the number of times areas have experienced the die-off phenomenon over that time, with warmer colors indicating
hot-spots of die-off activity, where the phenomenon is most frequent. The locations for the three sites used in this study are also shown.
Table 1. Seeded species, source information, and seed rates in both PLS/ft
and lbsPLS/ac for the single rate*
Species Germplasm origin Production
Single rate
Single rate
Fourwing saltbrush Humboldt County, Nevada Wild 2.9 2.0
Spiny hopsage Humboldt County, Nevada Wild 4.2 0.9
Bottlebrush squirreltail Klamath, Klamath
County, Oregon
6.9 2.2
Sandberg bluegrass Hanford, Benton
County, Washington
13.9 0.5
Yarrow Umatilla County, Oregon Lincoln
County, Washington
4.5 0.1
Royal penstemon Douglas County, Nevada Wild 2.5 0.2
Desert globemallow Utah Fresno, California 9.4 0.7
Total 44.3 6.5
*The double rate treatment consisted of the single rate applied twice.
Pure live seed (PLS) is % purity multiplied by % germination of the seed lot.
Multiply PLS/ft
by 10.76 for seed rate per square meter, and multiply lbsPLS/ac by 1.12 for kgPLS/ha.
2017 3
three treatment areas were established in each field: unseeded,
single seed rate, and double seed rate.
Six perennial native species of grasses, forbs, and shrubs
were selected for the seed mix used in the experiment due to
their commercial availability and likely suitability to one or
more of the sites (Table 1): scarlet globemallow (Sphaeralcea
ambigua),royalpenstemon(Penstemon speciosus), yarrow
(Achillea millefolium), Sandberg bluegrass (P. secunda), bottle-
brush squirreltail (E. elymoides), spiny hopsage (Grayia
spinosa), and four-wing saltbrush (Atriplex canescens). We
selected collections or cultivars that originated from sites that
were as similar as possible to the planting sites to maximize the
benefit from any locally adapted traits.
All sites were seeded the third week of November 2014
using a minimum-till Truax Flex II 86 drill mounted on a
tractor. The unseeded treatment was left completely undis-
turbed to represent site conditions that would occur with no
management intervention. The single rate treatment received
a total of approximately 44 pure live seeds per square foot
) applied with one seeder application, and the double
rate treatment received approximately 89 PLS/ft
applied in
two applications of 44 PLS/ft
each (Table 1). At the time of
planting in November 2014, cheatgrass seedlings were just
beginning to green up in all sites except the die-off field at
Four Corners.
All fields were monitored through two growing seasons, at 5
months (April 2015) and 16 months (March 2016) after seeding.
We sampled 20 randomly placed 1 m
quadrats in each treatment
to record densities for seeded and resident grasses, forbs, and
shrubs, as well as cheatgrass and other weeds. In June 2017, the
Four Corners site was monitored for the number of flowering
culms, following up on patterns observed in 2016. On a field-by
field basis, the sampled area was scaled down to a smaller area
(e.g., 10 cm × 10 cm for annual weeds) to reduce counting
fatigue if counts were likely to exceed several hundred.
Additionally, 25 randomly selected cheatgrass plants in each
field were measured in the first season for leaf number and
maximum leaf height.
A fully factorial analysis of variance model was used to
analyze the results separately for each sampling period, with
site (Buena Vista, Four Corners, Paradise), die-off condition
(control, die-off), and seeding treatment (unseeded,
single-rate, double-rate) as main effects.
Significance was
assessed at the P= 0.05 level.
Our Findings: Seeding Was More Successful
in Die-offs
Estimated precipitation for the three sites was 97% to
101%, 116% to 126%, and 144% to 158% of the 30-year
Figure 3. These images from the Four Corners site in April 2015 (top images) and March 2016 (bottom images) show reduced cheatgrass in the areas
that experienced die-off (left images) compared to unaffected controls (right images). In the first season, large and vigorous seeded native grass seedlings
could be seen in the die-off drill rows, while smaller seedlings were hidden in dense cheatgrass seedlings in the control. By the second year, these
differences were even more dramatic as seeded grasses began to fill the drill rows in the die-off and grow together. While the control still supported
seedlings, they were of a much smaller stature and grew amid much higher cheatgrass density.
average for each growing season, respectively.
We found
absolutely no seeded shrubs and an insignificantly small
number of seeded forbs surviving in our treatments, which
supports the notion that these kinds of species are particularly
challenging to establish, especially in highly invaded
However, our perennial grass species, Sandberg
bluegrass and bottlebrush squirreltail, did establish in
significant numbers, ranging from 3 to 48 seedlings/m
the first growing season to 0 to 20 seedlings/m
in the second
growing season (Figs. 3 and 4). In the second growing season,
the Four Corners site supported the highest establishment,
averaging 10 to 20 seedlings/m
, with the other two sites
showing similar densities of 0 to 11 seedlings/m
. Due to the
lack of forb and shrub establishment, the rest of this text is
focused only on the response of the seeded native grasses,
although we recommend future work be conducted to
understand the poor response of these species.
Our results strongly confirm what our previous case study
suggested, which is that die-offs significantly improve our
ability to establish native grasses from seed. We observed an
average of 280% more establishment of seeded native grasses in
the first season in die-off areas relative to controls, and this pattern
was consistent across all sites and seed rates (Fig. 4). In the second
growing season, this difference increased to over 500% more
seedlings in die-offs at two of the three sites, while the third site,
Four Corners, did not show such a pattern. The Four Corners site
visually supported the trend for improved success in die-offs
(Fig. 3), and the likely explanation for the lack of a difference in
density is that large seeded grasses in the die-off had grown
together and were difficult to differentiate from one another,
leading to an underestimation of seeded grass density in the die-off.
In the third growing season, counts of flowering culms of seeded
grasses at Four Corners were over 100-fold higher in the die-off
than in the control (Fig. 4), confirming greater success in the
die-off, despite the lack of difference in density in the second year.
Another important finding is that the patterns of native
grass establishment described were observed despite generally
intense competition with cheatgrass and/or other weeds in
die-off fields in both seasons (Fig. 3,Appendix A).
Additionally, our results were observed in exclosures that
prevented livestock from accessing seedings over the study
period. Although this rest from grazing is standard practice for
post-fire seedings, it remains to be seen if exclosures affect
seeding in die-off areas. Because fences are expensive and time
consuming to construct, we suggest that future research
determine how this practice affects restoration success in
die-off areas.
Our Findings: Increasing Seed Rates
Can Pay Off
Our results strongly suggest that increasing seeding
rates directly increased establishment. In the first growing
season, doubling the seed rate significantly increased the
number of seeded grasses in die-off as well as control
fields at the Buena Vista and Paradise sites by 145% to
437% (average 235%), with no effect at Four Corners (Fig. 4).
In the second growing season, the double-rate treatment
supported 133% to 425% (average 175%) more seedlings than
the single-rate treatment across all sites and fields, with the
exception of the control field at Buena Vista, where there was no
The double-rate treatment in our experiment was achieved
by applying the single rate twice. This is important to consider
because the extra cutting and packing of the soil or disturbance
to the thatch layer caused by an additional pass of the tractor
and seeder likely affected the seedbed conditions. These
effects may have been positive and may explain some or all of
the benefits of increased seeding rate, as well as why the Buena
Vista site supported three to four times more grasses due to a
Figure 4. Means and standard errors for number of live seedlings (left and middle) and number of flowering culms (right) of both squirreltail and Sandberg
bluegrass per square meter for each seed rate treatment (single, double) in areas that did not recently die off (control), as well as recent die-offs across
three study sites (Four Corners, Buena Vista, Paradise). Third-year data were only taken at the Four Corners site to clarify patterns observed in the second
year. Asterisks indicate significant (Pb0.05) differences between control and die-off fields (asterisks among the bars) and between single and double seed
rate treatments (asterisks below the bars) in analysis of variance models.
2017 5
mere doubling of the seed rate. Ideally, the double rate
treatment would have been applied in a single pass rather
than a double pass, but this was not feasible at the time
of seeding.
The two seed rates used in our experiment, 21 and 42 PLS/
for grasses, are both higher than the recommended rate for
a mixed stand involving these two species (~ 14 PLS/ft
Our findings suggest that the single rate was likely too low to
expect maximum success at our semi-arid, 203 to 254mm (8
to 10-in) annual precipitation sites, even in areas with reduced
cheatgrass competition. This is contrary to a more exhaustive
synthesis of restoration in this region, which found no benefit
to increasing similar seed rates for grasses.
However, James
and Svejcar
identified a need to research better seeding
technologies by demonstrating that the low success of drill
seeding methods may be because they do not place enough
seed at the best depth or into ideal seedbed conditions.
Although we support the need for improved seeding
technologies, our results suggest that in the meantime,
increasing seeding rates of traditional drill seeding may be
an easy way to increase success by exposing more seeds to
appropriate conditions.
Moving Forward with Die-off Restoration
Previous work has shown that die-offs are common,
although localized and unpredictable, and can affect tens of
thousands of hectares in some years.
These die-offs are
short-lived, with over 80% returning to cheatgrass dominance
in the next year. Die-offs also experience increases in the
densities of other annual forb weeds. However, despite this
seemingly hostile situation for native species, our research has
repeatedly shown that seeding of native perennial grasses in
the fall after a die-off results in greater success. Considering
that die-offs occur in highly invaded, low-diversity,
low-productivity ecosystems (commonly characterized as
hopeless candidates for restoration), the prospect of any
dependable method for increasing the success of native species
at these sites is welcome news. We propose that cheatgrass
die-off represents a large and underutilized opportunity to
improve establishment of native seedlings.
Cheatgrass die-offs can be thought of as one of several tools
in the revegetation toolbox and present a great opportunity to
focus restoration efforts. Because they are visible in freely
available satellite imagery as early as April/May, managers
could have 4 to 5 months to plan and prepare for seeding in
years with extensive die-offs, a considerable improvement on
post-fire seeding timelines. Prioritizing restoration in hot-
spotsof frequent die-off may further improve restoration
success, and optimizing seed mixes to suit these arid sites
might result in even greater establishment. For example, our
work clearly suggests that we need to do more to understand
barriers to shrub and forb restoration, as we had no success
with these seeds. Though more costly than seedings, die-offs
may be an area where transplanting forb and shrub seedlings
could establish islands within die-off hot-spots,
which could
increase natural recruitment when climatic conditions are
good for these species. Finally, post-seeding management may
further benefit these seedings. Pre-emergent herbicide or
targeted grazing may be useful for reducing annual weed
densities in the years following seeding, and these factors
could be tested in future experiments.
We suggest that landowners or managers experiencing
cheatgrass die-offs consider experimenting with seeding these
areas as a means of reintroducing native perennial species to
highly invaded, low-diversity lands, and we would be
interested in hearing reports of any successes or failures with
die-off seeding. Ongoing and future research should lead to
improved understanding of what causes die-offs and can
hopefully lead to useful predictions of when and where die-off
will occur, or even the ability to create new die-offs. In the
meantime, naturally occurring cheatgrass die-offs provide a
rare opportunity for active restoration in some of our most
degraded lands where, until recently, the potential for
improving rangeland resources and values has been considered
a lost cause.
The authors thank Jason Sprott for exceptional field
assistance, Rebecca Fritz for aiding in fence construction,
Dashiell Hibbard and Karin Kettenring for help monitoring
seeding success, Susan Meyer for stimulating conversation
and collaboration regarding our cheatgrass die-off work, and
one anonymous reviewer for helpful comments.
Appendix A.Weed Recovery after Die-off
Because the die-off phenomenon does not affect
dormant cheatgrass seeds, many sites return to cheatgrass
dominance in the next growing season. Additionally,
many forb weeds are excellent seed dispersers and appear
to do well in areas recovering from cheatgrass die-off.
Here, we report results of cheatgrass and other weeds in
our treatment plots.
In the first season, all sites supported significantly
greater densities of cheatgrass in the control than the
die-off fields (Fig. A1). In the second year, Four Corners
still strongly showed this trend, Paradise weakly showed
this trend in only two treatments, and Buena Vista had
uniform cheatgrass density across die-off and control
fields. The lower-density cheatgrass in the die-off in the
first season had significantly more culms per plant and was
significantly taller than in the control at all sites (Fig. A2).
These findings show that the cheatgrass present in
die-offs the year after the event is at a lower density but
has higher individual vigor than in adjacent areas that did
not die off and that these differences persist or fade away
by the second year, depending upon the site, all of which
corroborates previous findings.
Because of this quick
recovery, the window for restoration benefits after die-off
may be short.
Other weedy species responded to the die-off as well
(Table A1). All three sites had significantly higher densities of
other weed species in the die-off fields in the first year,
Appendix Figure A1. Means and standard errors for cheatgrass (top two panels) and weed (bottom two panels) density per square meter across seeding
treatments (unseeded, singlerate, double-rate) in areas that have not died-off (control, white bars) as well as recent die-offs (die-off, dark bars) across sites
(Four Corners, Buena Vista, Paradise) for both the first (left two panels) and second season (right panels). Values from the die-off field at the Buena Vista
site were exceptionally high and are noted above the bars. Note the difference in scale between the first and second year weed panels. Significant
differences between control and die-off fields in ANOVA models are indicated with asterisks (*P b0.05) and hashes (
Appendix Figure A2. Longest leaf (left) and number of culms per plant (right) for cheatgrass for the first season in areas that have not died-off (control,
white bars) as well as recent die-offs (die-off, dark bars) across sites (Four Corners, Buena Vista, Paradise). Significant differences between control and
die-off fields in ANOVA models are indicated with asterisks (*P b0.05).
2017 7
ranging from 37 to 296 plants/m
in the die-offs and from 1
to 50 plants/m
in the controls (Fig. A2). The density of other
weed species was generally higher when cheatgrass densities
were lower, suggesting that die-off events release other weed
species from the competitive dominance that cheatgrass
otherwise maintains. While the effect of the die-off on
cheatgrass densities began to fade at some sites in the second
growing season, this effect of die-offs on other weed densities
was stronger and consistent for both years at all sites.
The use of an undisturbed area for the unseeded treatment
prevented us from separating the physical effects of tractor and
seeder-related soil disturbance on weed densities from the
ecological effects (competition, facilitation, etc.) of the grass
seedlings on the dynamics of cheatgrass and other weeds; this
could be included in future experimental designs.
In summary, despite a complex interplay of cheatgrass and
weeds, the bottom line is that recent die-offs supported
dramatically increased establishment of seeded native grasses,
even though they were still infested with weeds and were
quickly returning to cheatgrass dominance.
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Appendix Table A1. List of exotic invasive (weeds), resident native, and introduced exotic species found to be
actively growing in samples at the three sites at the time of seeding (S) and in the first (1) and second (2) year
of monitoring.
Exotic invasive (weeds) Four Corners Buena Vista Paradise
Cheatgrass (Bromus tectorum) S, 1, 2 S, 1, 2 S, 1, 2
Field chickweed (Cerastium arvense) -22
Crossflower (Chorispora tenella) --1
Herb sophia (Descurainia sophia) 221
Redstem filaree (Erodium cicutarium) --2
Clasping pepperweed (Lepidium perfoliatum) 11,2-
Burr buttercup (Ranunculus testiculata) 1, 2 1, 2 2
Russian thistle (Salsola tragus) S, 1, 2 1 -
Tall tumblemustard (Sisymbrium altissimum) 1, 2 S, 1, 2 S, 2
Resident native
Bottlebrush squirreltail (Elymus elymoides) --S
Slender phlox (Microsteris gracilis) 11-
Sandberg bluegrass (Poa secunda) S, 1, 2 S S, 1, 2
Gooseberryleaf globemallow (Sphaeralcea grossulariifolia) S, 1, 2 - -
Small fescue (Vulpia microstachys) -1,2-
Introduced exotic
Crested wheatgrass (Agropyron cristatum) - S, 1 S, 1, 2
B. GEARY. 2014. Does Fusarium-caused seed mortality contrib-
ute to Bromus tectorum stand failure in the Great Basin? Weed
Research 54:511-519.
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dead zones in northern Nevada. Proceedings of the Society for
Range Management 64:94.
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-117.681459°E; 40.663527°N, -117.919296°E; 41.342562°N,
-117.601218°E. Available at:
18 November 2016.
Long-term effects of seeding after wildfire on vegetation in Great
Basin shrubland ecosystems. Journal of Applied Ecology
14. USDA NRCS (2016). Plant guide: Bottlebrush squirreltail
(Elymus elymoides) and Sandberg bluegrass (Poa secunda).
Available at: Accessed 17
October 2016.
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ecological sites: Regression analyses of seeded nonnative and
native species densities. Journal of Environmental Management
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seedling establishment: The role of seeding technology, water
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Authors are Research Faculty, University of Nevada, Reno,
Department of Natural Resources and Environmental Science. Reno
NV 89557 (Baughman,; Monitoring
Specialist, Bureau of Land Management, Winnemucca District
Office, Winnemucca, NV 89445 (Burton); Monitoring Specialist,
Bureau of Land Management, Salt Lake Field Office, West Valley
City, UT 84119 (Williams); Professor, University of Nevada, Reno,
Department of Natural Resources and Environmental Science, Reno
NV 89557 (Weisberg); Spatial Analyst/Research Scientist, University
of Nevada, Reno, Department of Natural Resources and Environ-
mental Science, Reno NV 89557 (Dilts); and Associate Professor,
University of Nevada, Reno, Department of Natural Resources and
Environmental Science, Reno NV 89557 (Leger). This work was
supported by the Great Basin Landscape Conservation Cooperative,
which had no active role in study design, data collection and analysis,
interpretation, or decisions to submit for publication.
2017 9
... Although people disagree about what causes the die-offs, most recognize these events may be opportunities for opportunities for reseeding rangelands invaded by cheatgrass with desirable species. 2 Cheatgrass die-offs are areas where cheatgrass is usually present but is absent for one or more growing seasons. Winter annual mustards (Brassicaceae) are also absent in die-off areas, and gray litter is usually present. ...
... 16,17 Over 80% of cheatgrass die-offs in northern Nevada from 1985 to 2015 were bare for only one year. 2 This suggests that die-offs are caused by a mobile or short-lived agent, rather than a sedentary or persistent one. ...
... Cheatgrass die-offs in northern Nevada from 1985 to 2015 also developed during dry winters and were more likely following 2, or even 3, years of below average precipitation. 2 These data suggest that similar conditions precede both cheatgrass die-offs and army cutworm outbreaks. ...
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On the Ground •Army cutworms consumed cheatgrass to produce cheatgrass die-offs at low elevations in southwest Idaho in 2014. The larvae also consumed foliage and bark of native shrubs. •Army cutworm outbreaks seem to occur after many adult moths lay eggs in areas experiencing drought, which received late summer rain to germinate winter annuals, but little subsequent precipitation through the following winter. •Army cutworms hide in plain sight by feeding at night in winter and hiding in soil or under objects during the day. •A network of observers in the Intermountain West could help rangeland managers identify die-offs for reseeding with desirable species.
The Enemy Release Hypothesis proposes that invasion by exotic plant species is driven by their release from natural enemies (i.e. herbivores and pathogens) in their introduced ranges. However, in many cases, natural enemies, which may be introduced or managed to regulate invasive species, may fail to impact target host populations. Landscape heterogeneity, which can affect both the population dynamics of the pathogen and the susceptibility and the density of hosts, may contribute to why pathogens fail to control hosts, despite established negative disease impacts. We explored patterns of post‐fire infection of the fungal head‐smut pathogen (Ustilago bullata) on the invasive annual cheatgrass (Bromus tectorum), which has caused the notorious grass‐fire cycle and ecosystem degradation across Western North America. We asked whether infection level was a driver of host density or vice‐versa, how weather affected infection, and how spatial patterns of infection varied with time since fire, using a combination of structural equation modeling (SEM), proportional odds modeling, and entropy‐based local indicator of spatial association (ELSA) on data from >700 plots spanning >100,000 ha remeasured annually for 4 years. Observed infection levels increased with greater prior‐year cheatgrass cover, and disease severity did not suppress cheatgrass populations. Warm, humid fall/winters and proximity to fire refugia (unburned patches) were associated with more infections. Infection clustering was most evident 2‐3 years following fire with warm‐wet fall‐winter conditions and decreased after two drier, colder winters. Synthesis: Disease severity in an invasive host did not result in a measurable reduction in its populations, which suggests that natural enemies may not strongly regulate this invasive species in its introduced range. Landscape heterogeneity associated with disturbance and weather limited population‐level infection of hosts by the fungal pathogen. Disturbance (specifically wildfire) and variable weather are key components of this and similar invasion systems, and likely need to be considered when evaluating disease dynamics and potential for natural enemies to influence invasion potential.
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Dryland ecosystems represent a significant portion of global land area, support billions of people, and suffer high rates of land degradation. Successfully restoring native vegetation to degraded drylands is a global priority and major challenge – highlighting the need for more efficient and successful restoration strategies. We introduce the concept of “precision restoration”, which targets critical biotic and abiotic barriers to restoration success and applies specific tools or methods based on barrier distribution in space and time. With an example from the sagebrush steppe biome, a North American cold desert, we present a framework for precision restoration in drylands that involves: 1) identifying site‐specific critical barriers to restoration success, 2) understanding the spatial and temporal variability of each barrier, and 3) applying the best available restoration strategies given the specific barrier and its variability, described in the first two steps. This framework aims to enhance restoration success by focusing restoration practices on ameliorating the influential barriers when and where they occur and away from applying singular landscape‐wide approaches. This article is protected by copyright. All rights reserved.
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Downy brome (cheatgrass) is a highly successful, exotic, winter annual invader in semi-arid western North America, forming near-monocultures across many landscapes. A frequent but poorly understood phenomenon in these heavily invaded areas is periodic 'die-off' or complete stand failure. The fungal pathogen Pyrenophora semeniperda is abundant in cheatgrass seed banks and causes high mortality. To determine whether this pathogen could be responsible for stand failure, we quantified late spring seed banks in die-off areas and adjacent cheatgrass stands at nine sites. Seed bank analysis showed that this pathogen was not a die-off causal agent at those sites. We determined that seed bank sampling and litter data could be used to estimate time since die-off. Seed bank patterns in our recent die-offs indicated that the die-off causal agent does not significantly impact seeds in the persistent seed bank.
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Bromus tectorum (cheatgrass) has widely invaded the Great Basin, U.S.A. The sporadic natural phenomenon of complete stand failure (‘die-off’) of this invader may present opportunities to restore native plants. A recent die-off in Nevada was precision-planted with seeds of the native grasses Poa secunda (Sandberg bluegrass) and Elymus elymoides (bottlebrush squirreltail), of both local and nonlocal origin, to ask: 1) Can native species be restored in recent B. tectorum die-offs? And 2) Do local and nonlocal seeds differ in performance? Additionally, we asked how litter removal and water addition affected responses. Although emergence and growth of native seeds was lower in die-off than control plots early in year one, in year two, seedlings in die-offs had increased vigor and growth, at equal or higher densities, than control plots. Local seeds consistently outperformed nonlocal seeds for P. secunda, whereas for E. elymoides, nonlocal showed an advantage in the first season, but in the second season, there were more local seeds present under die-off and unraked conditions. Seedbed treatments affected performance, but did not notably improve establishment or modify other results. Our results warrant further investigation into die-off restoration as well as recognition of the importance of seed source selection in restoration.
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Bromus tectorum (cheatgrass, downy brome) is an important invader in western North America, dominating millions of hectares of former semi-arid shrubland. Stand failure or ‘die-off’ is relatively common in monocultures of this annual grass. The study reported here investigated whether soil-borne pathogens could be causal agents in die-offs. Soils from two die-off areas and adjacent B. tectorum stands were used in a glasshouse experiment with sterilised and non-sterilised treatments. Soil sterilisation did not increase emergence, which averaged 80% in both die-off and non-die-off soils. Seedling biomass was higher in die-off soils, probably due to increased nitrogen availability. Fusarium was isolated from 80% of killed seeds in non-sterilised soil treatments. In pathogenicity tests with 16 Fusarium isolates, host seeds incubated under water stress (−1.5MPa for 1 week prior to transfer to free water) suffered over twice the mortality of seeds incubated directly in free water (25–83% with water stress vs. 5–43% without water stress). These results suggest that soil-borne Fusarium could play a role in B. tectorum stand failure in the field, but that low water stress conditions in the glasshouse experiment were not conducive to high levels of disease. Pathogenic Fusarium isolates were obtained from seeds planted in both die-off and non-die-off soils, suggesting that microenvironmental factors that affect levels of water stress might be as important as relative abundance of soil-borne pathogens in mediating spatial patterns of disease incidence in the field.
The exotic annual grass Bromus tectorum (cheatgrass) dominates vast acreages of rangeland in the western USA, leading to increased fire frequency and ecosystem degradation that is often irreversible. Episodic regeneration failure (“die-off”) has been observed in cheatgrass monocultures and can have negative ecosystem consequences, but can also provide an opportunity for restoration of native species and ecological function within the imperiled sagebrush steppe ecosystem. Proximate causes of cheatgrass die-off are uncertain, although several taxa of fungal soil pathogens have been implicated. Die-off occurrence is stochastic and can occur in remote areas. Thus, developing remote sensing indicators that are repeatable over long time periods, across extensive regions, and at relatively fine spatial resolution would be beneficial for accurately pinpointing events.
Within the sagebrush steppe ecosystem, sagebrush plants influence a number of ecosystem properties, including nutrient distribution, plant species diversity, soil moisture, and temperature, and provide habitat for a wide variety of wildlife species. Recent increases in frequency and size of wildfires and associated annual grass expansion within the Wyoming big sagebrush alliance have increased the need for effective sagebrush restoration tools and protocols. Our objectives were to quantify the success of Wyoming big sagebrush transplants relative to transplant stock (nursery seedlings vs. wildlings) across different ecological sites and vegetation types and to test the hypothesis that reduction of herbaceous vegetation would increase survival of transplanted sagebrush. We used a randomized block (reps=5) design at each of three sites-1) cheatgrass dominated, 2) native plant dominated, and 3) crested wheatgrass dominated-near Elko, Nevada. Treatments included plant stock (nursery stock or locally harvested wildlings) and herbicide (glyphosate) to reduce competition from herbaceous vegetation. Transplants were planted in the spring of 2009 and 2010 and monitored for survival. Data were analyzed for site and treatment effects using mixed-model ANOVA. Surviving plant density at and 2 yr postplanting was generally highest (up to 3-fold) on the native site (P < 0.05). Density of surviving transplants was almost 3-fold higher for nursery stock on most sites for the 2009 planting, but differences in survival by planting stock were minimal for the 2010 planting. Glyphosate application increased surviving plant density up to 300% (depending on site) for both years of planting. High labor and plant material investments (relative to traditional drilling or broadcasting) may limit the size of projects for which sagebrush transplants are practical, but these costs may be partially offset by high success relative to traditional methods. Our data indicate that sagebrush transplants can be effective for establishing sagebrush on depleted sites.
Understanding cheatgrass (Bromus tectorum) dynamics in the Northern Great Basin rangelands is necessary to effectively manage the region’s lands. This study’s goal was to map and monitor cheatgrass performance to identify where and when cheatgrass dieoff occurred in the Northern Great Basin and to discover how this phenomenon was affected by climatic, topographic, and edaphic variables. We also examined how fire affected cheatgrass performance. Land managers and scientists are concerned by cheatgrass dieoff because it can increase land degradation, and its causes and effects are not fully known. To better understand the scope of cheatgrass dieoff, we developed multiple ecological models that integrated remote sensing data with geophysical and biophysical data. The models’ R2ranged from 0.71 to 0.88, and their root mean squared errors ranged from 3.07 to 6.95. Validation of dieoff data showed that 41% of pixels within independently developed dieoff polygons were accurately classified as dieoff, whereas 2% of pixels outside of dieoff polygons were classified as dieoff. Site potential, a long-term spatial average of cheatgrass cover, dominated the development of the cheatgrass performance model. Fire negatively affected cheatgrass performance one year postfire, but by the second year postfire performance exceeded prefire levels. The landscape scale monitoring study presented in this paper helps increase knowledge about recent rangeland dynamics, including where cheatgrass dieoffs occurred and how cheatgrass responded to fire. This knowledge can help direct further investigation and/or guide land management activities that can capitalize on, or mitigate the effects of, cheatgrass dieoff.
Invasive annual grasses alter fire regimes in shrubland ecosystems of the western USA, threatening ecosystem function and fragmenting habitats necessary for shrub-obligate species such as greater sage-grouse. Post-fire stabilization and rehabilitation treatments have been administered to stabilize soils, reduce invasive species spread and restore or establish sustainable ecosystems in which native species are well represented. Long-term effectiveness of these treatments has rarely been evaluated.We studied vegetation at 88 sites where aerial or drill seeding was implemented following fires between 1990 and 2003 in Great Basin (USA) shrublands. We examined sites on loamy soils that burned only once since 1970 to eliminate confounding effects of recurrent fire and to assess soils most conducive to establishment of seeded species. We evaluated whether seeding provided greater cover of perennial seeded species than burned–unseeded and unburned–unseeded sites, while also accounting for environmental variation.Post-fire seeding of native perennial grasses generally did not increase cover relative to burned–unseeded areas. Native perennial grass cover did, however, increase after drill seeding when competitive non-natives were not included in mixes. Seeding non-native perennial grasses and the shrub Bassia prostrata resulted in more vegetative cover in aerial and drill seeding, with non-native perennial grass cover increasing with annual precipitation. Seeding native shrubs, particularly Artemisia tridentata, did not increase shrub cover or density in burned areas. Cover of undesirable, non-native annual grasses was lower in drill seeded relative to unseeded areas, but only at higher elevations.Synthesis and applications. Management objectives are more likely to be met in high-elevation or precipitation locations where establishment of perennial grasses occurred. On lower and drier sites, management objectives are unlikely to be met with seeding alone. Intensive restoration methods such as invasive plant control and/or repeated sowings after establishment failures due to weather may be required in subsequent years. Managers might consider using native-only seed mixtures when establishment of native perennial grasses is the goal. Post-fire rehabilitation provides a land treatment example where long-term monitoring can inform adaptive management decisions to meet future objectives, particularly in arid landscapes where recovery is slow.
Since the mid-1980s, sagebrush rangelands in the Great Basin of the United States have experienced more frequent and larger wildfires. These fires affect livestock forage, the sagebrush/grasses/forbs mosaic that is important for many wildlife species (e.g., the greater sage grouse (Centrocercus urophasianus)), post-fire flammability and fire frequency. When a sagebrush, especially a Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis (Beetle & A. Young)), dominated area largely devoid of herbaceous perennials burns, it often transitions to an annual dominated and highly flammable plant community that thereafter excludes sagebrush and native perennials. Considerable effort is devoted to revegetating rangeland following fire, but to date there has been very little analysis of the factors that lead to the success of this revegetation. This paper utilizes a revegetation monitoring dataset to examine the densities of three key types of vegetation, specifically nonnative seeded grasses, nonnative seeded forbs, and native Wyoming big sagebrush, at several points in time following seeding. We find that unlike forbs, increasing the seeding rates for grasses does not appear to increase their density (at least for the sites and seeding rates we examined). Also, seeding Wyoming big sagebrush increases its density with time since fire. Seeding of grasses and forbs is less successful at locations that were dominated primarily by annual grasses (cheatgrass (Bromus tectorum L.)), and devoid of shrubs, prior to wildfire. This supports the hypothesis of a “closing window of opportunity” for seeding at locations that burned sagebrush for the first time in recent history.