Biological mediation of invasive plant impacts in ecosystems Duane A. Peltzer Landcare 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

After Cote et al 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 Oikos 118: 1001

Dickie et al 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 unpublished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

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 GCB 16:732.