Understanding the Role of Resource Limitation
in Restoration of Sagebrush Ecosystems
Invaded by Cheagrass (Bromus tectorum L.)
Jeanne Chambers, Rachel Jones, Dave Board, Dale
Johnson, and Bob Blank
WHY LIMIT RESOURCES?
 Common disturbances - removal of native
species and fire - increase resources
 Cheatgrass is highly responsive to N
availability
o Early germination, higher growth and
reproductive rates than natives
 Native perennial species are more
tolerant of resource limiting conditions
 N reduction may decrease competitive
from invaders & benefits natives

Seeds of natives & conditions for
establishment required
EFFECTS OF FIRE ON NITROGEN
Surface inorganic - N
20
a
Kg ha
-1
ab
15
abc
10
cde
5
de
cd
bc
de
0
2001
2002
de
e
2003
2004
2005
Available N increased from ~
17 lbs/ac to 80-100 lbs/ac for 3 years
(Rau et al. 2007, also Stubbs & Pyke 2005)
EFFECTS OF PERENNIAL GRASSES & FORBS
R2 = 0.15***
R2=0.49****
R2=0.39****
Perennial Native Herbaceous
Cover in Year 0 (%)
(Chambers et al. 2014)
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2003
Undershrub
Interspace
Increase in biomass
and seeds ~
 Removal – 2 to 3 fold
 Burning – 2 to 6 fold
 Removal + Burning
–10 to 30 fold
Burn Control Burn Control Burn Control
6400'
7180'
7800'
(Chambers et al. 2007)
5 0%
10
0%%
50 0%
10
0%%
50 0%
10
0%%
50 0%
10
0%%
50 0%
10
180
160
140
120
100
80
60
40
20
0
2002
0%%
50 0%
10
0%%
50 0%
10
0%%
50 0%
10
0%%
50 0%
10
0%%
50 0%
10
0%%
50 0%
10
No. Seeds/Plant Biomass/plant (g)
CUMULATIVE EFFECTS OF
FIRE & REMOVAL
Burn Control Burn Control B
6400'
7180'
APPROACHES FOR LIMITING RESOURCES
 Direct manipulation of soil resources
o Carbon amendments
 Encourage population growth of soil
microbes to tie up soil N
o Repeated burning
 Immediate N pulse due to SOM denaturation,
uptake by plants, volatilizing N in soils
& biomass causing progressive N deficiency
 Litter removal
o Modulate soil temperature and moisture increasing SOM
decomposition and its removal decreases soil N availability
o Decrease seed bank & provide less favorable environment
for establishment
 Seeding competitors with similar phenology
o Decrease resource availability (water, N, light)
EXPERIMENT #1 – RESOURCE AND
PROPAGULE AVAILABILITY
How do resource availability (inorganic N) and
propagule availability influence establishment of
cheatgrass and native perennial species?
 Wyoming big sagebrush/Sandbergs bluegrass dominated
by cheatgrass, 4600 ft elevation, 9-11 in precipitation
 Carbon addition - 150 g C m2 sucrose or none
 Different seeding densities
o B. tectorum (0, 150, 300, 600, and 1,200 viable seeds m2)
o Native species (0, 150, 300, and 600 viable seeds m2)
Shrub - Artemisia tridentata ssp. wyomingensis
Forbs - Achillea lanulosa, Sphaeralcea grossularifolia
Grasses- Poa secunda, Elymus multisetus, Pseudoroegneria
spicata
 Repeated in two years
EFFECTS OF SUCROSE ADDITION
Short-term effects on
available N

Higher NO3- in winter
months

Repeated applications
necessary for longer
term effects
(Mazzola et al. 2010, also
Pashke et al. 2000,
Blumenthal et al. 2003,
Blank and Young 2009)
EFFECTS OF SUCROSE ADDITION &
CHEATGRASS SEEDING DENSITY
Negative effect of sucrose
on cheagrass density,
biomass & seed production
Positive effect of seeding
density
 Cheat density not
affected by native
seeding rate
(Mazzola et al. 2010)
EFFECTS OF SUCROSE ADDITION &
CHEATGRASS SEEDING DENSITY
 Little to no effect of sucrose
on native density & growth
 Negative effect of
cheatgrass seeding density
EFFECTS OF NATIVE SEEDING DENSITY
Positive effect of native
seeding density on
establishment only in first year


Reaffirms importance of
seedling life stage
Common seeding rates
are 150 to 300 seeds m2 –
2 to 3 times that may be
required
(Mazzola et al. 2010; also
Sheley et al. 2006)
EXPERIMENT #2 –
DIRECT AND INDIRECT RESOURCE
MANIPULATION
How do restoration treatments to reduce resources (repeated
burning, litter manipulation, seeding an annual competitor) affect
soil N availability & cheatgrass success?
 Wyoming big sagebrush/Sandbergs bluegrass dominated by
cheatgrass, 4600 m elevation, 9-11 in precipitation

 Litter intact and litter removed experiments
 Repeated burning and seeding treatments nested within litter





Not burned and not seeded (N)
Burned and not seeded (B)
Burned and seeded with cheatgrass (C)
Burned and seeded with wheat (W)
Burning repeated over 4 years at 2 sites
EFFECTS ON AVAILABLE SOIL N
 Available N did not decrease over
time - soil temperatures were too
cool to volatilize soil OM
 Available N was lower on unburned
than burned plots regardless of
treatment
EFFECTS ON LITTER
Litter biomass (g m-2)
1200
1000
Litter removed plots
Litter intact plots
1200
Litter intact, unburned
Litter intact, burned only
Litter intact, burned and seeded with cheatgrass
cheatgras
Litter intact, burned and seeded with wheat
1000
800
800
a
600
a
b
b
b
400
200
a
b
b
b
0
2008
2009
2010
600
Litter intact, unburned
Litter removed, unburned
Litter removed, burned only
Litter removed, burned and seeded with cheatgrass
cheatgrass
Litter removed, burned and seeded with wheat
a
a
a
400
a
ab
b
b
2011
b
b
b
2012
 Burning caused 30 to 50%
litter loss each year
(Jones et al. 2014, in press)
200
0
b
b
b
b
b
b
b
b
2009
2010
a
b
bc
bc
c
2011
b
c
c
c
2012
EFFECTS ON CHEATGRASS BIOMASS
 Cheat biomass, & seed production tracked N
availability over time
 Litter removal decreased biomass & density
 Plots burned and seeded with wheat had
consistently lower biomass, density, seeds
PUTTING IT ALL TOGETHER
PUTTING IT ALL TOGETHER
PUTTING IT ALL TOGETHER
PUTTING IT ALL TOGETHER
IMPORTANCE FOR RESTORATION
Integrated restoration approaches to limit resources & decrease
cheatgrass establishment may be more effective than
manipulating soil N directly
 Carbon amendments reduce N and limit cheatgrass while
allowing native establishment but have short term effects
 Repeated burning does not decrease available soil N due to
cool burn temperatures and does not directly affect cheatgrass
 Litter removal decreases cheatgrass density, biomass and
seed production
 Seeding a competitor with similar growth characteristics is
highly effective in reducing cheatgrass success
 Higher seeding rates or more effective planting methods of
natives may be required
 Weather determines outcomes & multiple interventions may be
needed
The preceding presentation was delivered at the
2015 National Native Seed Conference
Santa Fe, New Mexico April 13-16, 2015
This and additional presentations available at
http://nativeseed.info