Robert Steers & Edith Allen
UCR
The role of resource heterogeneity on native
plant response to invasive plant removal
“Fertile Island Effect”
Increased SOM, Soil Moisture, and Soil Nutrients
Moderated Temps, Decreased PAR
Invasive plant abundance is positively
correlated with resource availability (Davis et
al 2000, Bashkin et al. 2003, Deahler 2003,
Foster and Dickson 2004, Colautti et al. 2006)
Competition intensity is positively correlated
with resource availability (Grime 1979, Belcher
et al. 1995, Aerts 1999)
Species richness is negatively correlated
with resource availability within the range of
resource availability between shrub and
interspace microhabitats (Huston 1979)
Objectives
Determine which microhabitat will have the
greatest:
-invasive species abundance
-competition intensity
-native annual plant richness
-relative increase in native plant richness once
all invasive plants are removed
Bromus madritensis spp. rubens
(Red Brome)
Schismus arabicus & S. barbatus
(Schismus)
Brassica tournefortii
(Sahara Mustard)
Erodium cicutarium
(Filaree)
Grass Site
Brassica Site
2005
Erodium Site
2008 Native Site
2008
2008
8m
METHODS
•Four Sites
•Randomized block design
8m
•12 blocks
•Plots centered on creosote
shrubs
Plots treated once, early
in growing season
Vegetation sampled at
end of growing season
TREATMENTS
1. Control
C
2. Total invasive plant removal: Fusilade II
(grass-specific herbicide) plus invasive forb
removal by hand R
There is evidence that Fusilade II is lethal
to Erodium spp. so we also implemented:
3. Fusilade II alone F
138.1 mm
ar
ch
M
ay
Ap
ril
M
Fe
br
ua
ry
ry
3.8 mm
Ja
nu
a
2008 (Sep. ‘07 - May ‘08)
40
20
0
M
ay
h
M
ay
M
ar
c
M
ay
Fe
br
ua
ry
Ja
nu
ar
y
N
ov
em
be
r
D
ec
em
be
r
O
ct
ob
er
Se
pt
em
be
r
Ap
ri l
0
A
pr
il
20
Ap
ril
40
M
ar
ch
60
M
ar
ch
80
Fe
br
ua
ry
ry
100
Fe
br
ua
ry
ry
N
ov
em
be
r
D
ec
em
be
r
Ja
nu
a
60
Ja
nu
a
80
O
ct
ob
er
N
ov
em
be
r
D
ec
em
be
r
100
O
ct
ob
er
Precip. (mm)
285.2 mm
be
r
O
ct
ob
er
No
ve
m
be
r
De
ce
m
be
r
2007 (Sep. ‘06 - May ‘07)
S
ep
te
m
be
r
79.8 mm
Precip. (mm)
(Sep. ‘05 - May ‘06)
Se
pt
em
be
r
2006
Precip. (mm)
(Sep. ‘04 - May ‘05)
Precip. (mm)
2005
Se
pt
em
PRECIPITATION
Average = 126.2 mm (5 in)
100
80
60
40
Grass Site:
Treatments
Applied 2005
20
0
100
80
60
40
20
0
*
Other Sites:
Treatments
Applied ‘08
***
Invasive plant abundance is greatest in the understory
Competition intensity is greater in the understory, but not always
Native annual plant richness is greater in the interspace
Relative increase in native richness is greatest in the understory
Invasive plant abundance
Competition intensity
Relative increase in native richness
Native annual plant richness
Modified form Kieft et al. 1998
Invasive Plant - Fire Feedback Cycle
1973, 1984, 2004
Fuel Break
1973, 1984
FUSILADE II
Biomass at treatment application time
0% Erodium
Biomass at peak season
Biomass (g) per m²
in flower
50
40
70% Erodium
in flower
*
*
30
20
10
*
0
E. cicutarium
Schismus
spp.
Grass
Site
05
Grass
Site
2005
Grass
Site
2004-05
E. cicutarium
Schismus
spp.
Filaree
Site
08
Erodium
Site
2008
Erodium
Site
2007-08
Native Spp. per 0.5 m²
10
Native Species Richness
9
8
b
7
6
5
ab
b
b
a
4
ab
3
b
b b
b
a
a
a
a
a
2
1
0
Grass '05
Grass '06
Grass'08
Filaree '08
C
Control
F
Fusilade II
R
Total Invasive Removal
Mustard '08
Native '08
70
Native Annual Plant Cover
Native % Cover
60
50
b
40
b
b
b
b
30
20
b
a
b b
10
a
b
a
a a
a
0
Grass '05
Grass '06
Grass'08
Filaree '08
C
Control
F
Fusilade II
R
Total Invasive Removal
Mustard '08
Native '08
Invasive Grass % Cover
70
a
Invasive Grass Cover
60
50
40
30
a
20
b b
10
a
b b
a
b b
b b
0
Grass '05
Grass '06
Grass'08
Filaree '08
C
Control
F
Fusilade II
R
Total Invasive Removal
Mustard '08
Native '08
Fusilade II
Control
Invasive Forb Cover
70
Invasive Forb % Cover
a
a
60
50
a
40
a
30
b b
20
b
10
b b
0
Grass '05
Grass '06
Grass'08
Filaree '08
C
Control
F
Fusilade II
R
Total Invasive Removal
Mustard '08
Native '08
Conclusions
1. Understories:
- are more invaded
- can experience greater competition intensity, but not
always
- are less speciose
- generally exhibit a greater relative increase in native
annual plant richness when invasives are removed
These findings suggests that more productive microhabitats
might gain the most from invasive plant control and
restoration efforts.
Conclusions
2. In sites with low invasive abundance, natives don’t
respond to the invasive plant removal. Although, it is
generally more efficient to control invasives at the
earliest stage of their spread.
3. Fusilade II is lethal to Erodium spp, especially when
applied before inflorescence initiation.
4. Where Erodium spp. and grasses are the most abundant
invasive plants, Fusilade II shows great potential as a
restoration tool.
5. If treatments are applied in a very wet year, treatment
effects can last for at least 4 yrs.
Acknowledgements
Edith Allen and Lab
Jodie Holt and Lab
Richard Minnich
Andy Sanders
Cameron Barrows