Biological mediation of invasive plant impacts in ecosystems

Duane A. PeltzerLandcare Research

Lincoln, New Zealand

1.NZ weeds and ecosystem processes

2.What are weed impacts?

3.Field removal experiments

What is covered in this talk?

NZ Background

• > half of NZ’s flora is naturalised non-native plants; many are weeds

• Weeds are widely thought to reduce biodiversity and alter ecosystem processes

• >340 weed species are currently managed

IMPACT = DISTRIBUTION x ABUNDANCE x

EFFECT

Predicting weed impact

Least well understood, include:• Gene-flow• Biogeochemical changes (C, N, P)• Disturbance regime• Ecosystem engineers• Interaction modification

Weed effects

Understanding what controls the ecosystem-level impacts of exotic species as a basis for management

Invasion Ecology

root feeding fauna

mycorrhiza

pathogens

direct pathway to plants indirect pathway to plants

detritus foodweb

a

c1c2

b1b2

After Cote et al. 2005 ARES

Modest effects

Reversible threshold effects

Non-reversible threshold(different stable states)

Kowhai River, Kaikoura, NZ

Dominant exotic

Buddleja davidiiCoriaria arborea

Dominant native

~97% of total plant biomass

~15 species<0.1% of biomass

~25 species~3% of biomass

Other exotics Other natives

Peltzer et al. 2009 Oikos 118: 1001

+C+B+N +C+B-N +C-B+N -C+B+N -C+B-N -C-B+N

+C-B-N

-C-B-N

Nat

ive

alph

a di

vers

ity (

spec

ies

richn

ess)

0

4

6

2

2002 2003 2004 2005

a b

2002 2003 2004 2005

Year

+C+B+N +C+B-N +C-B+N -C+B+N -C+B-N -C-B+N

+C-B-N

-C-B-N

Nat

ive

alph

a di

vers

ity (

spec

ies

richn

ess)

0

4

6

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2002 2003 2004 2005

a b

2002 2003 2004 2005

Year

Dickie et al. 2010 New Phytologist

Nematode community shifts

Dehlin et al. 2008

Preferred Not selected Avoided

Forsyth et al. 2002, Richardson et al. unpublished

Kurokawa, Peltzer, Wardle 2010 Functional Ecology

Kurokawa, Peltzer, Wardle 2010 Functional Ecology

PossumsRats

Vegetation/fruit

Inverts?

Birds

Control

Key points

• Small species matter!

• Weeds have biological legacies + change ecosystem processes (effects)

• Containment or early control is best

Peltzer et al. 2010 GCB 16:732.