Predicting invasive weed species what matters

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Predicting invasive weed species what matters?
Weed symposium Southern Cross Dunedin 3rd
November 2004

• William Lee,
• Private Bag 1930,
• Landcare Research,
• Dunedin

With help from Peter Williams, Richard Duncan,
Jon Sullivan and Tristan Armstrong
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Why do we need to be able to predict invasive
weeds?
Prediction or pragmatics?

• Border control
• Prioritisation
• Cost benefit
• Legislation (HSNO, Biosecurity, Conservation
  Acts)

Weed Risk Assessment Risk probability of
becoming a weed x impact
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Risk to what?

• Natural environment (Biodiversity)
• Human health
• Agribusiness

Risk distinct from potential benefits
Risk assessment only half the answer Politics/econ
omics is the other half Keep the two distinct
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Weed Risk Assessment Risk probability of
becoming a weed x impact
Fact or fiction?
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Elements of current WRA

• Biogeography
• Domestication/cultivation
• Climate and distribution
• Weed history
• Biology/ecology
• Undesirable traits
• Plant type
• Reproduction
• Dispersal
• Persistence

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Border control

• All new plant species
• Score
• Accept
• Evaluate
• Reject

To date it has been used to approve 2 new species
and reject 1 application for 11 Agathis species
gt 95 success rate in Hawaii
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Legislation and WRA will reduce cross-border flow
but we have enough sleepers here to worry about
Auckland - Esler
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Plant naturalization

• Critical step
• Self-sustaining populations
• Biological invasion stage, devoid of value
  judgments

Can we make generalisations?
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New Zealand
Figures rounded
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Naturalization clumped within genera

• Genus was a significant (p lt 0.01) predictor for
  12 of 13 families with more than 50 introduced
  genera
• E.g., Asteraceae, Fabaceae, Liliaceae
• Myrtaceae an exception

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Naturalisation scources
Anywhere there is mass planting of introduced
species
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Most crops become naturalised
Australia 17 United Kingdom 30 Fitzjohn,
Armstrong, and Newstrom
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Naturalization rate and weediness
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Trifolium species in New Zealand (Kelly Gravuer,
Duncan, Sullivan and Williams)
Global
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Accidentally introduced naturalised
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What matters at each invasion stage? (use data on
distribution, life-history, ecology and
human-use of Trifolium species)

• Intentionally introduced species, those that
  naturalised
• greater introduction effort (more ha planted)
• were better matched to NZ climate

• Relative to other species, accidentally
  introduced naturalised clovers are
• better matched to NZ climate
• native to human-influenced habitats
• more widely distributed in Britain
• capable of self-pollination

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• Naturalised species with a faster rate of spread
• are more frequently found as pasture seed
  contaminants
• have a larger native range
• have a longer flowering period in NZ
• These three traits explain 86 of the
  variation in multiple regression

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Predicting invasiveness in naturalised woody
plants Experimental approach

• Species
• Fabaceae (broom, lupin, gorse 7 spp)
• Mimosaceae (Acacia 4 spp)
• Pinaceae (larch, fur, pines 16 spp)
• Rosaceae (Rosa, blackberry 6 spp)

Treatments Fertilizer, drought, shade, clipping,
burning, competition, fertilizer plus
competition, fertilizer plus clipping, and control
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• Hypothesis
• invasiveness associated with higher RGR and
  better survival
• wider tolerance of local conditions

Results no significant relationship between
seedling RGR or survival or tolerance across
treatments and invasiveness (ER occupied)
Previous work on Pinus had shown a positive
relationship between RGR and naturalisation,
perhaps reflecting selection for fast-growing
species for forestry.
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Naturalisation

• Most species will become naturalised
• Largely a result of propagule pressure or
  planting effort
• Do so initially near human settlements
• Small contribution from traits

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Spread

• Key role for humans
• e.g., roads, animals, landuse etc
• Environmental potential and traits increasingly
  important
• Generally occurs over decades
• Models for predicting potential range

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Springboard sites Key sites for subsequent
human-assisted spread of weeds
Lupin Broom Gorse Pampas grass
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Rate and pattern of spread will reflect types of
reproduction
Populus alba
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Predicting persitence
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Predicting Impact

• Function of
• Spread/extent
• Ability capture resources or modify disturbance
• Novelty
• Level of natural disturbance
• Degree of community alienisation

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Depends of goal for the site

• For biodiversity need to think about
• Long-term indigenous dominance
• Use natural successions
• Reflect on value of seral communities
• Role of existing management
• Particular vegetation

Greatly reduce the number of significant
environmental weeds
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Systems based on available resources and spread
stage
Williams et al.
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Invasive genes

• Primary escape routes
• GM crops themselves may become weedy and
  invasive (greater than non-GM?)
• Gene flow from GM to non-GM crop of the same
  species via pollination (crop management)
• Gene-flow to wild relatives via hybridisation
• (preliminary analyses)

Fitzjohn, Armstrong, and Newstrom
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Potential for crop-wild hybridisation in NZ

• Survey of 147 major NZ crops and their wild
  relatives present in local flora
• 289 wild relatives
• 252 naturalised exotics
• 37 native taxa
• Approach
• MAY close relatives
• CAN experimental hybridisations
• DO evidence of natural hybridisation

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Hybridisation
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Hybridisation with native taxa?

• Only three studies to date
• Celery can hybridise with Apium prostratum
  (native celery)
• Potato incompatible with 2 natives
• (Solanum aviculare, S. laciniatum)
• 3. Rasberry and blackberry incompatible with 2
  natives (Rubus australis R. squarrosus)

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Genera likely to contain compatible crop-native
combinations

• Agrostis
• Festuca
• Rubus
• Less likely, but possible
• Daucus
• Linum
• Oxalis
• Passiflora

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Predicting invasive weeds - what matters?

• Humans particularly at the early and most
  tractable phases of invasion
• Clearly articulated rationale, i.e why?
• WRA models are remarkably accurate (vastly better
  than economic predictions)

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Need to overcome the first law of human
behavioural ecology
In general humans, collectively or individually,
will not control weeds until they are severely
interferring with some actual or perceived valued
activity