Weed spread in New Zealand

Jon SullivanLincoln University

sullivaj@lincoln.ac.nz

Weed spread•New Zealand is still in the early

stages of plant invasion•Weed spread occurring across

many scales; different processes dominate at each

•We need better ways of predicting the what, where, and when of weeds

•We lack long-term monitoring data necessary to understand spread

Source: Hal Mooney

National naturalisation Data: Hazel Gatehouse, unpub.

1991–2000• 164 new plant species naturalised(avg. 143 per decade 1851-1990)

include:

• 18 annuals/biennials (41.4)

• 43 herbaceous perennials (54.1)

• 78 shrubs and trees (36.1)

• 150 ornamental

4 forestry,1 hort.

Car

toon

: Auc

klan

d R

egio

nal C

ounc

il

Source: Michael Mulvaney (2001), in Groves et al. (eds.), Weed risk assessment, CSIRO Publishing, Collingwood, Australia.

Lag phase, SE Australia

Source: Michael Mulvaney (2001), in Groves et al. (eds.), Weed risk assessment, CSIRO Publishing, Collingwood, Australia.

Propagule pressure, SE Australia

•All naturalised species.

1 2 3 4 5 6 7 8 9 10

Most species in <3 provinces

?

0

2

4

6

8

10

100 150

Years since naturalisation500

avg ± std. error

Province scale (NZ)

0

100

200

300

400

500

600

700

1840 1860 1880 1900 1920 1940 1960 1980 2000

total speciesaccidental introductions

horticultural introductionsagricultural introductions

Esler (1987)

Year

City scale: Auckland

1840 1860 1880 1900 1920 1940 1960 1980 2000

Year ofnaturalisation

d

N = 308

N = 339

N = 270

abundant

scarce

rare

***

***

avg.± std. error

City scale: AucklandData: Alan Esler and Ewen Cameron

Settlement scale: Northland N.Z.J. Ecology, 29:1–10 (2005)

DOC weeds on roadsides

Should we be alarmed?

•Scenario 1: Most ornamentally-sourced naturalised plants are dependent on the habitats in and around urban areas and will remain there.

•Scenario 2: Most ornamentally-sourced naturalised plants are in the early stages of invasion.

Spread modelling examples

•Pest spread (John Keane, Jake Overton)

•Porter’s Pass Hawthorn (John Keane, Peter Williams, Rowan Buxton)

•Wilding pines (Yvonne Buckley, Nick Ledgard, et al.)

•Craigieburns Hieracium lepidulum (Alice Miller PhD)

Dispersal mechanisms

•National/provincial scales: People•City scales: People + natural

dispersal•Local scales: People + natural

dispersal

Sandra Anderson’s starlings

•Collected seeds under starling roosts from two Auckland islands, Tiritiri Matangi and Motuihe, both dominated by native plants

•Tiritiri: 20% seed exotic •Motuihe: 65% seed exotic

The hitchhikers’ guide to dispersal

•Nursery industry and informal plant trade

•Garden waste dumping•Seed contaminants in/on seed, hay,

produce, farm stock•In and on road and railway vehicles•Attached to people and their

equipment

people = new naturalisations

close correlation between province population and naturalisation

Population biases in the sites of recently naturalised plants:

0

5

10

15

20

1945 1966 1991 1996 2001

Year

real

random

± 95% C.I.

New plants where people were

Some questions•Where, when, and at what scales is

weed spread usefully predictable, and for what weeds? What time-series data needs to be collected?

•To what extent can we infer the likely mechanism(s) of spread from spatial distribution data?

•What is the relative contribution of human and natural dispersal vectors for the spread of different weeds, at different scales?

Weed spread•New Zealand is still in the early

stages of plant invasion•Weed spread occurring across

many scales; different processes dominate at each

•We need better ways of predicting the what, where, and when of weeds

•We lack long-term monitoring data necessary to understand spread