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

Transcription

1 Out of the frying pan: Invasion of exotic perennial grasses in coastal prairies Jeffrey D. Corbin 1, Meredith Thomsen 1, Janice Alexander 2 and Carla M. D Antonio 3 1 UC Berkeley 2 UC Extension 3 UC Santa Barbara

2 Exotic annuals Exotic annual grasslands

3 Exotic perennial grasses: An even greater threat?

4 Holcus lanatus Velvet grass Range maps courtesy of Calflora

5 Phalaris aquatica Harding grass

6 Festuca arundinacea Tall fescue

7 Dactylis glomerata Orchard grass

8 Cal-IPC Categories List 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

9 Impacts of exotic perennial grasses Ability to invade coastal ecosystems Ability to displace native species Challenges for restoration and management

10 Invasion Exotic annual grasslands

11 Invasion Coastal scrub

12 Invasion Remnant coastal prairies

13 Invasion Percent cover in a native-dominated coastal prairie Tom s Point Preserve Percent cover Holcus Phalaris F. arundinacea Dactylis Percent cover Percent cover Percent cover D Antonio, unpub.

14 Invasion Holcus establishment in coastal prairies: Does species composition matter? Bromus carinatus Festuca rubra (also created bare plots) Calamagrostis nutkaensis

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

16 Invasion M. Thomsen, unpub. Total Holcus seedlings sampled a a b b 0 bare BC CN FR 2002: F 3,63= ; p< : F 3,63= ; p<.0001 cover bare BC CN FR

17 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

18 Impacts of exotic perennial grasses Ability to invade coastal ecosystems Ability to displace native species Challenges for restoration and management

19 Displacing natives Competition Experiment Natives only Natives + Exotics Exotics only Marin County, CA 1.5 m x 1.5 m plots Established in 1998 Monitored for 4 years

20 Displacing natives Natives vs. exotic perennials Aboveground productivity per plant (g) A. oregonensis 20 F. rubra * * * * N. pulchra * * * Natives only Natives + Exotic perennials Corbin and D Antonio, unpub.

21 Displacing natives Exotic perennials vs. natives Aboveground productivity per plant (g) Holcus lanatus 16 Phalaris aquatica Festuca arundinacea * p < * Exotic perennials only Exotic perennials + Natives

22 Displacing natives Ability to displace natives Asymmetric competitive interactions favor exotic perennials Observations that invaded habitats can be virtually monocultures

23 Impacts of exotic perennial grasses Ability to invade coastal ecosystems Ability to displace native species Challenges for restoration and management

24 Out of the frying pan

25 and into the fire?

26 Land-use changes associated with rapid invasions Removal of grazing Sea Ranch Pt. Reyes Bodega Marine Reserve

27 Land-use changes associated with rapid invasions Removal of grazing Sea Ranch Pt. Reyes Bodega Marine Reserve Addition of grazing may not favor native perennial grasses

28 Land-use changes associated with rapid invasions Removal of grazing Sea Ranch Pt. Reyes Bodega Marine Reserve Addition of grazing may not favor native perennial grasses Burning

29 Cover Fires favor exotic perennials especially Holcus Broom control technique Alexander and D Antonio 2002

30 Recommendations for List A Rapid invaders Widely observed Displace natives YES Disrupt natural habitats YES Exotic annual grasslands Coastal scrub Native-dominated prairie

31 Thanks to: Audubon Canyon Ranch Bodega Marine Reserve Funding: National Science Foundation Marin Community Foundation

32 Invasion Holcus lanatus abundance Sea Ranch Foin & Hektner 1986 Ungrazed Grazed % % % 0%