Evaluating Critical Uncertainty Thresholds in a Spatial Model of Forest Pest Invasion Risk

Authors

  • Frank H. Koch,

    1. Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC, USA, and Forest Health Monitoring Program, USDA Forest Service, Research Triangle Park, NC 27709, USA.
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  • Denys Yemshanov,

    Corresponding author
    1. Natural Resources Canada, Canadian Forest Service, Great Lakes Forestry Centre, Sault Ste. Marie, Ontario P6A 2E5, Canada.
      *Address correspondence to Denys Yemshanov, Natural Resources Canada, Canadian Forest Service, Great Lakes Forestry Centre, 1219 Queen Street East, Sault Ste. Marie, Ontario P6A 2E5, Canada; tel: 705-541-5602; fax: 705-541-5700; dyemshan@nrcan.gc.ca.
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  • Daniel W. McKenney,

    1. Natural Resources Canada, Canadian Forest Service, Great Lakes Forestry Centre, Sault Ste. Marie, Ontario P6A 2E5, Canada.
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  • William D. Smith

    1. Southern Research Station, USDA Forest Service, Research Triangle Park, NC 27709, USA.
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*Address correspondence to Denys Yemshanov, Natural Resources Canada, Canadian Forest Service, Great Lakes Forestry Centre, 1219 Queen Street East, Sault Ste. Marie, Ontario P6A 2E5, Canada; tel: 705-541-5602; fax: 705-541-5700; dyemshan@nrcan.gc.ca.

Abstract

Pest risk maps can provide useful decision support in invasive species management, but most do not adequately consider the uncertainty associated with predicted risk values. This study explores how increased uncertainty in a risk model's numeric assumptions might affect the resultant risk map. We used a spatial stochastic model, integrating components for entry, establishment, and spread, to estimate the risks of invasion and their variation across a two-dimensional landscape for Sirex noctilio, a nonnative woodwasp recently detected in the United States and Canada. Here, we present a sensitivity analysis of the mapped risk estimates to variation in key model parameters. The tested parameter values were sampled from symmetric uniform distributions defined by a series of nested bounds (±5%, … , ±40%) around the parameters' initial values. The results suggest that the maximum annual spread distance, which governs long-distance dispersal, was by far the most sensitive parameter. At ±15% or larger variability bound increments for this parameter, there were noteworthy shifts in map risk values, but no other parameter had a major effect, even at wider bounds of variation. The methodology presented here is generic and can be used to assess the impact of uncertainties on the stability of pest risk maps as well as to identify geographic areas for which management decisions can be made confidently, regardless of uncertainty.

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