Download - Weed spread in New Zealand
Weed spread in New Zealand
Jon SullivanLincoln University
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