Out of the frying pan: Invasion of exotic perennial grasses in coastal prairies

Jeffrey D. Corbin1, Meredith Thomsen1, Janice Alexander 2 and Carla M. D’Antonio3

1UC Berkeley2UC Extension

3UC Santa Barbara

Exotic annuals

Exotic annual grasslands

Exotic perennial grasses:

An even greater threat?

Holcus lanatusVelvet grass

Range maps courtesyof Calflora

Phalaris aquaticaHarding grass

Festuca arundinaceaTall fescue

Dactylis glomerataOrchard grass

Cal-IPC CategoriesList A: “Most aggressive invaders that displace

natives and disrupt natural habitats”

List B: “Invaders that spread less rapidly and cause a lesser degree of habitat disruption”

Current classification• Holcus lanatus – List B• Festuca arundinacea – List B• Phalaris aquatica – List B• Dactylis glomerata – NONE

Impacts of exotic perennial grasses

• Ability to invade coastal ecosystems

• Ability to displace native species

• Challenges for restoration and management

Exotic annual grasslandsInvasion

InvasionCoastal scrub

Invasion

Remnant coastal prairies

Invasion

Percent cover in a native-dominated coastal prairie – Tom’s Point Preserve

Perc

ent c

over

0

5

10

15

20

25

30Holcus Phalaris F. arundinacea Dactylis

Perc

ent c

over

0

5

10

15

20

25

30

1999 2000 2001 2002 2003

Perc

ent c

over

0

5

10

15

20

25

30

1999 2000 2001 2002 2003

Perc

ent c

over

0

5

10

15

20

25

30

1 2

3 4

D’Antonio, unpub.

Invasion

Bromuscarinatus

Calamagrostisnutkaensis

Festucarubra

Holcus establishment in coastal prairies:Does species composition matter?

(also created bare plots)

Invasion

• Allowed plants to establish for two years, then invaded with Holcus seeds

Invasion

cover

bare BC CN FR

Tota

l Hol

cus

seed

lings

sam

pled

0

2

4

6

8

10

12

14

16

18

bare BC CN FR

2002 2003a

a

b

b

2002: F 3,63=16.1495; p<.00012003: F 3,63= 13.0992; p<.0001

M. Thomsen, unpub.

Ability to invade coastal ecosystems

• Exotic perennials able to invade a variety of coastal ecosystems

• Ability to invade varies with community composition

• Disturbed habitats particularly vulnerable

Impacts of exotic perennial grasses

• Ability to invade coastal ecosystems

• Ability to displace native species

• Challenges for restoration and management

Competition ExperimentDisplacing natives

Nativesonly

Exoticsonly

Natives+

Exotics

• Marin County, CA

• 1.5 m x 1.5 m plots

• Established in 1998

• Monitored for 4 years

Natives vs. exotic perennialsDisplacing natives

Natives onlyNatives + Exotic perennials

1999 1999-2000 2000-2001 2001-20020

5

10

15

20

1999 1999-2000 2000-2001 2001-2002

Abo

vegr

ound

pro

duct

ivity

per

pla

nt (g

)

0

5

10

15

20 A. oregonensis F. rubra

1999 1999-2000 2000-2001 2001-20020

1

2

3

4 N. pulchra

* *

**

* * *

Corbin and D’Antonio, unpub.

Exotic perennials vs. nativesDisplacing natives

1999 1999-2000 2000-2001

Abo

vegr

ound

pro

duct

ivity

per p

lant

(g)

-5

0

5

10

15

1999 1999-2000 2000-20010

10

20

30

40

1999 1999-2000 2000-20010

2

4

6

8

10

12

14

16Holcus lanatus Phalaris aquatica Festuca arundinacea

*

*

p < 0.10

Exotic perennials onlyExotic perennials + Natives

Ability to displace nativesDisplacing natives

• Asymmetric competitive interactions favor exotic perennials

• Observations that invaded habitats can be virtually monocultures

Impacts of exotic perennial grasses

• Ability to invade coastal ecosystems

• Ability to displace native species

• Challenges for restoration and management

Out of the frying pan…

…and into the fire?

Land-use changes associated with rapid invasions

• Removal of grazingSea RanchPt. ReyesBodega Marine Reserve

Land-use changes associated with rapid invasions

• Removal of grazingSea RanchPt. ReyesBodega Marine Reserve

• Addition of grazing may not favor native perennial grasses

Land-use changes associated with rapid invasions

• Removal of grazingSea RanchPt. ReyesBodega Marine Reserve

• Addition of grazing may not favor native perennial grasses

• Burning

Fires favor exotic perennials –especially Holcus

Broom control technique

Cov

er

Alexander andD’Antonio 2002

Recommendations for List A• Rapid invaders – Widely observed

• Displace natives – YES

• Disrupt natural habitats – YESExotic annual grasslandsCoastal scrubNative-dominated prairie

Thanks to:Audubon Canyon RanchBodega Marine Reserve

Funding:National Science FoundationMarin Community Foundation

Invasion

Holcus lanatus abundanceSea Ranch – Foin & Hektner 1986

Ungrazed Grazed

1974 6-11%

1976 15%

1978 21-23% 0%