Risk Analysis for Tamarisk Control Strategies

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Risk Analysis for Tamarisk Control Strategies

• by
• James F. Fairchild
• Presented at USGS Partnership Meeting,
  Albuquerque, NM.Aug. 27, 2003

U.S. Department of the Interior U.S. Geological
Survey
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Columbia Environmental Research Center
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CERC Interest in Tamarisk Issue

• Ecological risk assessment of herbicides
• Development of analytical chemistry methods
• Environmental fate of herbicides
• Modeling, empirical assessment
• Efficacy trials with herbicides

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Professional Background

• Research Aquatic Ecologist, 20 years
• Non-target effects of pesticides in experimental
  ecosystems
• Fate of pesticides (e.g. triclopyr, atrazine,
  metribuzin, etc.)
• Efficacy of herbicides for invasive plants
  (Salvinia molesta)
• Ecological risk assessment for endangered species
  including fish, invertebrates, amphibians, and
  plants

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Colorado River Near Moab, Utah
Courtesy of Tom Till Gallery
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Tamarisk Control Measures

• Mechanical removal
• Prescribed fire
• Biological controls
• Herbicide application
• Combinations of approaches

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Mechanical Control

• Pros
• Can rapidly remove large numbers of trees
• Trees can be moved and piled for burning or other
  use
• Can be used to prepare site for re-vegetation
• Cons
• Extremely destructive of soils and wildlife
  habitat
• Dangerous for operators
• Can be expensive and logistically difficult

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Prescribed Fire Control

• Pros
• Emulates natural processes that can benefit
  native species
• Removes remaining woody debris
• Facilitates subsequent re-vegetation efforts
• Cons
• Can result in property loss
• Causes short-term habitat loss
• Public and agencies may not accept as widespread
  tool

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Biological Control

• Pros
• Uses natural predator adapted to the target
  species
• Fewer non-target impacts on other species and
  habitat
• No concerns over groundwater contamination
• Cons
• Requires importation of non-native species
• Success varies depending on environmental factors
• Benefits may not be observed in acceptable time
  frame

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Chemical Control

• Pros
• Can be remotely applied
• Minimal physical disturbance
• Can be conducted with volunteer efforts with
  training
• Cons
• Concern over water/groundwater contamination
• Causes temporary physical impacts on habitat
• Concern over non-target chemical impacts

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Framework for Risk Assessment
Source U.S. Environmental Protection Agency and
SETAC, 1998
Problem Formulation
Data Gathering and Analysis
Risk Characterization
Discussions Risk Assessor and Risk Manager
Risk Management
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Chemical Risks

• Risk to applicator
• Risk for groundwater contamination (humans)
• Risk to livestock (meat/milk contamination)
• Risk to non-target endangered plants and crops
• Non-target non-target birds and mammals
• Non-target fish toxicity

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Problem Formulation Example Risk to Endangered
Fish Species

• Use of herbicides may have non-target risks to
  endangered fishes.
• How sensitive are fish to the herbicide?
• Are fish likely to be exposed?
• How can risk be minimized?

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Data gathering and analysis

• Toxicity testing for species sensitivity
• How sensitive are endangered species
• Chemical efficacy testing on tamarisk
• How much is applied?
• How is it applied?
• Chemical exposure modeling
• Where does chemical go and for how long

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Multi-Species Sensitivity Distribution
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Probabilistic risk assessment major risk
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Probabilistic risk assessment minor risk
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Herbicides Used for Tamarisk Control
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Herbicides Used for Tamarisk Control
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Chemical Application Methods

• Foliar spray
• Granular applications
• Stump cut and paint
• Basal bark injection

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Efficacy and Cost/Risk Tradeoffs
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Range of Potential Conditions

• Rangelands (livestock commercial crops)
• Alluvial plains (groundwater concerns)
• Canyon walls (limited access)
• Riparian corridors (wildlife habitat)
• Refuge wetlands (endangered species)
• Military sites (unexploded ordinants)

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Exposure/Risk Minimization

• Conduct appropriate risk analysis
• Use of efficacious chemical
• Use of efficacious dose
• Optimization of chemical application procedures
• Amount applied
• How applied
• When applied

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Conclusions

• Tamarisk is enormous problem
• Multiple control approaches needed
• Each control method has risks and benefits
• Risks can be evaluated and minimized in a
  science-based framework
• Successful tamarisk removal program will involve
  science and the public in a partnership