Out of the frying pan: Invasion of exotic perennial grasses in coastal prairies · 2017-12-14 ·...
Transcript of Out of the frying pan: Invasion of exotic perennial grasses in coastal prairies · 2017-12-14 ·...
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%