Belowground perspectives in southern

California grassland restoration

Sara Jo M. Dickens

Department of Environmental Science, Policy and

Management, University of California, Berkeley

Edith B. Allen

Department of Botany and Plant Sciences, Center for

Conservation Biology, University of California, Riverside

Modified from Wolfe and Klironomos 2005 Bioscience

Native Exotic

Type conversion Increased fire frequency

The impact an exotic plant has on an ecosystem depends on how different it is from the

dominant native plant species. (Ehrenfeld 2003; Wardle et al 2004)

Loss of habitat and diversity

Altered nutrient pools and cycling Altered soil microbial community

Altered litter quality and quantity

Altered water infiltration

Objectives

• Determine changes in soil ecology (mycorrhizae, nutrients, soil seedbank) caused by invasive species, and ability to restore soil biological and chemical characteristics

• Restore grasslands and forblands historically grazed and farmed, currently with high exotic grass cover

• Test various techniques: mulch, herbicide, grazing, dethatching, mowing, solarization, fire

Microbial

community composition was

altered by invasion.

PC1

-4 -2 0 2 4 6 8 10 12P

C2

-3

-2

-1

0

1

2

3Restored

Invaded

PC1

-8 -6 -4 -2 0 2 4 6 8

PC

2

-3

-2

-1

0

1

2

3

4

PC1: P= 0.001

PC2: P= 0.041

Inla

nd

Gra

ssla

nd

Co

asta

l G

rassla

nd

F:B ratio was altered

by invasion , but the direction depended

on season.

Mycorrhizal inoculation

experiment

Avena roots have dominant

Glomus geosporum spores,

Stipa roots have equal

abundance of three species.

Five months after inoculation,

both grass species recovered

their mycorrhizal species

composition, showing rapid

response by the fungi. (Nelson & Allen 1993)

Glomus deserticola

AVENA GRASSLANDSTIPA INOC AVENA INOC UNINOC

0

10

20

30G. GEOSPORUM

G. ALBIDUM

G. DESERTICOLA

SP

OR

ES

/ 5

g S

OIL

A. AVENA PLANTS

STIPA GRASSLANDSTIPA INOC AVENA INOC UNINOC

0

10

20

30

G. GEOSPORUM

G. ALBIDUM

G. DESERTICOLA

SP

OR

ES

/ 5

g S

OIL

B. STIPA PLANTS

Establishing Stipa requires control of Avena,

even with mycorrhizal inoculum

Stipa monoculture

Avena dominates

in mixture, Stipa dies

Invasion Alters Nitrogen Availability

• Invaded soils had reduced extractable nitrogen.

• Nitrogen cycling rates were increased by invasion.

B

ug

N/g

so

il

0

10

20

30

40

50

60

NH4

NO3

A

IN REB IN REB IN REB

C

D

F

E

BA

F

E

D

C

B A

ug

N/g

so

il

0

10

20

30

40

50

60

IN IN INREW REW REW

Germination Peak Senescence

B AC

D

AB

IN = Invaded REB = Restored by burn REW = Restored by weeding

Riverside-Perris Plain

Anthropogenic nitrogen deposition elevates soil mineral N, causing

increased biomass of exotic grasses relative to native species

Vegetation response following the 1993 fire at Lake Skinner plus N fertilization and control (no

fertilization). p is repeated measures probability, * is p = 0.05 by year.

EXOTIC GRASSES

0

20

40

60

80

100

120

140

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2008 2009 2010

% c

over

plus N

control

*

* *

* **

*

P = 0.001

NATIVE FORBS

0

20

40

60

80

100

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2008 2009 2010

% c

over

plus N

control

**

*

*

*

*

P = 0.025 (minus 1994)

Plus N

Control

Nitrogen fertilization increased exotic grass cover and

reduced native cover

Mulch can be used to:

•immobilize excess N

•decrease exotic grass cover

•increase establishment of native

plants

•bark was more effective than

straw

Seedbank of exotic grassland, native CSS with grass understory,

and adjacent burned and unburned sites after the

October 2003 fire, Shipley Reserve.

Average Seedlings per m2

Species Grassland Shrubland Unburned Burned

Exotic Grasses 7261 3932 7339 147

Exotic Forbs 4714 1126 1440 969

Native Forbs 407 800 211 121

Native shrubs 14 0.5 6.3 0

Exotic seeds overwhelm native seedbank. Fire reduces exotic

grass seedbank, providing a window of opportunity for restoration (Cox and Allen 2008).

• Fire and weeding increased native richness and cover, but not substantially.

• Seedbank germination experiments show limited native species richness, indicating the need for seeding.

2006 2007 2008 2009

Non-n

ative r

ichness p

er

0.5

m2

0

2

4

6

8

Unburned

Burned

Burned + Weed

Native r

ichness p

er

0.5

m2

0

2

4

6

8

10

A

B

B

AB

A

B

A

A

B

B

A

A A

B

A

B

A

A

B B

B

Limited Soil Seedbanks

Controlling the Exotic Grass Seedbank

Methods • Grazing

• Grass-specific herbicide

• Mowing

• Dethatching

• Solarization

Prescribed Fire

(Hervey 1949; Gillespie & Allen 2004; Moyes et al. 2005; White et al. 2006 )

Properly timed prescribed burns can removal 90% of exotic seed input and reduce thatch.

Grass-specific herbicide

(Fusilade)

Dethatching treatment to

remove standing litter

Sheep grazing to

control exotic

grass

200 sheep per hectare

for 2 days in Mar/Apr

Exotic grass and exotic forb cover after two years of Fusilade application (‘99, ‘00) and 3 years of sheep grazing (‘99, ‘00, ‘01).

1. Grazing was not effective until the third year because of drought 2. Native forbs were consumed by sheep, but recovered from seedbank 3. Thatch removal had no positive effect. 4. Grasses began to recover from grazing and herbicide after 2 years 5. Native forb response to herbicide still positive after 4 years

QuickTime™ and aGraphics decompressorare needed to see this picture.

1999 2000 2001 2002 2003 2004

0

10

20

30

40

50

60

Control

Fusilade

Thatched Fusilade

Grazing

Exotic Grass %Cover

a

ab

a

a

aa

a

a

b

b

bb

bc

caa

a

a

a

aa

b

QuickTime™ and aGraphics decompressorare needed to see this picture.

1999 2000 2001 2002 2003 20040

5

10

15

20

25

30

35

40Control

Fusilade

Thatched Fusilade

Grazing

Native Forbs %Cover

a

aa

aaaa

a

b

b

b

b

ba

aaa a

a

cc

bb

a

Solarization in Abandoned Agricultural Land

• 6 x 6 m sheets applied Nov. 2004

• Removed Jan. 2005 and native forb seed mix applied (tidy tips dominate)

Apr. 2005 Feb. 2005 Nov. 2004

Herbicide

Mowed Control

0

20

40

60

80

100

120

140

Unplowed Plowed Control Manual Herbicide Solarize

Treatment

% C

over

Nonnative spp.

Native spp.

a

d

cd

bc

b

Bcd

C

AB

A

AB

B

Solarized

Solarization was the

most effective method

for exotic seedbank

control

Conclusions

• Mycorrhizal fungi spore species composition recovered

within 5 months of revegetation with Stipa pulchra, however,

inoculation with mycorrhizal fungi did not overcome negative

completive effects of exotic annual grasses on Stipa growth.

• Extractable nitrogen, nitrogen cycling rates and microbial

community composition also recovered within a growing

season following exotic grass removal.

• Nitrogen deposition and elevated soil N from past fertilization

increases productivity of exotic annual grasses, with

concomitant reduction in native forb productivity.

• Mulches to immobilize soil N and control of exotic grasses

are effective, but the best large scale solution is to control N

deposition.

Conclusions (continued)

• Seed bank control of exotic grass is the most urgent need.

Solarization is the most effective method, but works only in

tilled, level land and moist soil (abandoned agriculture in

winter-spring months)

• Grazing is only effective in years with sufficient grass

productivity. Grazed native forbs recover from the seedbank

and exotic grasses recover from grazing after 2 years.

• Fusilade is an effective treatment for control of Bromus, Avena

and Schismus but not Vulpia. It also controls Erodium spp.

Conclusions (continued)

• Early season mowing and disking can be used to control

exotic grasses.

• Spring fire is most effective to control the seed bank, but

fall fire is also effective especially if combined with

seeding.

• Any of these exotic grass control methods will require

reapplication at intervals of 2-5 years depending on

effectiveness of the initial treatment.

Citations Allen, E. B., S. A. Eliason, V. J. Marquez, G. P. Schultz, N. K. Storms, C. D. Stylinski, T. A. Zink, and M. F. Allen. 2000. What

are the limits to restoration of coastal sage scrub in Southern California. Pages 253-262 in J. E. Keeley, M. Baer-

Keeley, and C. J. Fotheringham, editors. 2nd Interface between ecology and land development in California. US

Geological Survey.

Allen, E.B., R. D. Cox, T. Tennant, S. N. Kee and D. H. Deutschman. 2005. Landscape restoration in southern California

forblands: Response of abandoned farmland to invasive annual grass control. Israel Journal of Plant Sciences 53:237-

245.

Cione, N. K., P. E. Padgett, and E. B. Allen. 2002. Restoration of a native shrubland impacted by exotic grasses, frequent

fire, and nitrogen deposition in southern California. Restoration Ecology 10:376-384.

Cox, R.D. and E.B. Allen. 2008. Composition of soil seed banks in southern California coastal sage scrub and adjacent

exotic grassland. Plant Ecology 198: 37-46.

Cox, R.D. and E.B. Allen. 2008. Stability of exotic annual grasses following restoration efforts in southern California coastal

sage scrub. Journal of Applied Ecology 45: 495-504.

Cox, R.D. and E.B. Allen. 2011. The roles of exotic grasses and forbs when restoring native species to highly invaded

southern California annual grassland. Plant Ecology 212:1699-1707.

Dickens, S.J.M. 2010. Invasive plant-soil feedbacks and ecosystem resistance and resilience: A comparison of three

vegetation types in California. PhD dissertation, University of California Riverside.

Gillespie I.G., and E.B. Allen. 2004. Fire and competition in a southern California grassland: impacts on the rare forb

Erodium macrophyllum. Journal of Applied Ecology. 41: 643-652.

Gillespie, I.G. and E.B. Allen. 2006. Effects of soil type and mycorrhizae from native and invaded vegetation on a rare

California forb. Applied Soil Ecology 32:6-12.

Gillespie, I.G. and E.B. Allen. 2008. Restoring the rare forb Erodium macrophyllum to exotic grassland in southern

California. Endangered Species Research 5: 65-72.

Marushia, R.G. and E.B. Allen. 2011. Control of exotic annuals to restore native forbs in abandoned agricultural lands.

Restoration Ecology 19:45-54.

Nelson, L. L., and E. B. Allen. 1993. Restoration of Stipa pulchra grasslands: effects of mycorrhizae and competition from

Avena barbata. Restoration Ecology 1:40-50.