Weed%20Risk%20Assessment%20for%20non-botanists

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Weed Risk Assessment for non-botanists Peter
A.Williams Landcare Research Nelson, New
Zealand Williamsp_at_landcareresearch.co.nz
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Definitions

• Weed a plant species controlled ( or potential
  to be so) because of its impact
• Impact interference with human health, economy,
  or environment etc.
• Weed risk probability x intensity of weed
  impact
• Invasiveness spatial spread

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Invasion is crossing barriers

• Human responses love it or hate it
• Spatial continents to farm-scale
• Biological pollinators, dispersers etc.
• Environmental temperature, nutrients etc.

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Four Elements of Risk

• Probability - likelihood, chance
• Uncertainty - the unknowable
• Consequences - impact in space and time
• Manageability - resources, timing

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Constraints to weed prediction

• Uniqueness of species x environment matches
• Non-reoccurring events
• Not measurable directly prior to invasion
• Continuous change through time

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Science, sociology,economics
People
Pathways
Weed-risk assessment
Plants
Habitats
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lt 1 spp.per year p.a.
16 spp.per year
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WRA opportunities
Risk component Pre entry Post entry
Probability Low High
Uncertainty High Low
Consequences Estimate Measurable
Manageability Estimate Measurable
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Elements of a Pre Border WRA

• Origin of the plant and climate match
• History of the species
• Pathways of introduction
• Establishment and spread likelihood
• Impacts features

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WRA outcome thresholds and examples
Score range Outcome Example species Actual score
lt 1 Accept Camelia -14
1-6 Evaluate Cineraria 1
1-6 Reject Gorse 22
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Table 1. Accuracy rates for weeds and non-weeds
using the WRA system from various studies outside
Australia (with locally-adapted questions but
without the decision tree of Daehler et al.,
2004). Sensitivity is the percentage of known
weed species which had a reject outcome.
Specificity is the percentage of known non-weed
species which had an accept outcome.
Study Sensitivity ( true weeds predicted) Specificity ( true non-weeds predicted)

Pheloung et al. 1999 69 92
Daehler and Carino 2000 90 54
Daehler et al. 2004 ? 66
Jefferson et al. 2004 100 40
Krivanek and Pysek 2006 73 71
Mean ?? 65
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Elements of a Post Border WRA

• Evaluate weed risks
• Invasiveness criteria
• Impacts criteria
• Potential distribution
• Feasibility of control
• Current distribution
• Costs and duration
• Weed management priorities
• Weed risks versus feasibility of control

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Mathematics and Post Border WRA

• Evaluate weed risks
• modelling traits
• modelling spread
• environment matching
• Feasibility of control
• optimum search strategies
• determining real costs
• Weed management priorities
• cost benefit analysis