Advances in Threat Assessment and Their Application to Forest and Rangeland Management
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Previous Pests/Biota Syntheses GENERAL TECHNICAL REPORT PNW-GTR-802 This page is intentionally left blank. 420 Advances in Threat Assessment and Their Application to Forest and Rangeland Management Representing Human-Mediated Pathways in Forest Pest Risk Mapping Frank H. Koch and William D. Smith Using the sudden oak death pathogen (Phytophthora ramorum) and other pests as examples, we illustrate how Frank H. Koch, research assistant professor, Department some of these data sources can be employed for mapping of Forestry and Environmental Resources, North Carolina risks associated with human-mediated pathways. First, we State University, Research Triangle Park, NC 27709; and demonstrate the use of foreign import cargo statistics— William D. Smith, quantitative research ecologist, USDA, marine, airborne, and transborder—to assess the risk of Forest Service, Southern Research Station, Research introduction of new species at United States ports of entry. Triangle Park, NC 27709. Second, we examine the utility of inland waterway cargo Abstract statistics, freight analysis networks, and other databases on domestic commodity traffic for mapping regional and local Historically, U.S. forests have been invaded by a variety of spread of forest pests. Third, we explain the diverse applica- nonindigenous insects and pathogens. Some of these pests tions of business databases, not only to identify clusters of have catastrophically impacted important species over a high-risk businesses, but also to rank these businesses using relatively short timeframe. To curtail future changes of this a suite of socioeconomic factors. Finally, we discuss the magnitude, agencies such as the U.S. Department of Agri- limited availability of up-to-date land use/landcover data, culture Forest Service have devoted substantial resources and present alternative data sources for representing high- to assessing the risks associated with recent or potential risk areas of current urbanization as well as the forest-urban forest invaders. These assessments of risk typically include interface. a mapping component; among other things, this presents Whereas many of these data sets are imperfect depic- a useful way to organize early-detection/rapid-response tions of human-mediated pathways, integration of several procedures. However, forest pest risk mapping is often can add significant depth to early-detection/rapid-response limited to readily available and manageable data sets, which projects. To facilitate further applications, we discuss user results in representations of risk that heavily favor climatic considerations, future information needs, and potential factors or estimates of host species distribution. Detailed sources of additional data regarding human-mediated examinations of human-mediated pathways of spread are pathways. often neglected in forest pest risk analyses owing to a lack Keywords: Commodities, dispersal, forest pests, of spatial data or uncertainty about a pest’s predictive model freight, human-mediated, risk, WUI. parameters. Humans are the most important facilitator of forest pest Introduction introduction and spread. With expanding global trade and In 2000, annual forest losses and control costs in the United interstate commerce, the number of potential forest invaders States due to nonindigenous forest insects and pathogens is likely to rise, making the analysis of human-mediated were estimated at $4.3 billion (Pimentel and others 2000), pathways particularly timely. In this synthesis, we present a and that figure is likely to rise due to the increasing trans- number of spatial data sources, collected by Federal agen- port of species beyond their native habitats (Brockerhoff cies and private companies for a range of purposes, which and others 2006b). In ecological terms, these pests alter can be utilized to represent these human-mediated path- forest composition, structure, and productivity; in some ways. Although general in nature, queries can often be used cases, pests basically remove host tree species from forest to tailor these data sets to address specific pests. Perhaps, ecosystems (Brockerhoff and others 2006b, Levine and most importantly, the source data can usually be acquired D’Antonio 2003). A case in point is the once-dominant for free or at negligible cost. American chestnut (Castanea dentata (Marsh.) Borkh.), 421 GENERAL TECHNICAL REPORT PNW-GTR-802 which was virtually eliminated from eastern forests by template for the design of regulatory programs and detec- chestnut blight (Cryphonectria parasitica) within 50 years tion surveys or, if a pest has already been established in of the pathogen’s introduction from Asia (Liebhold and one part of the geographic area of interest, through control others 1995). Over a similar timeframe, the hemlock woolly tactics that prioritize areas for which the risk of pest spread adelgid (Adelges tsugae Amnand) has caused extensive is the highest (Andersen and others 2004a). mortality throughout the Northeastern United States and has recently spread into the southern Appalachian Importance of Human-Mediated Pathways Mountains, raising fears that it will decimate both eastern Pest risk maps are typically assembled using spatial data hemlock (Tsuga canadensis (L.) Carriere) and Carolina from three principal subject areas: host species distribu- hemlock (T. caroliniana Engelm.) populations in the region. tion, environmental factors affecting pest persistence (e.g., Notably, the adelgid was considered a mere nuisance pest of climate), and pathways of pest movement (Bartell and Nair ornamental hemlocks for a few decades after its accidental 2004). Risk maps often focus on climatic factors or host introduction around 1953, until it began to spread to natural species distribution or both (e.g., Meentemeyer and others forest stands during the mid-1980s (Souto and others 1996). 2004), perhaps because of a lack of information regard- A related pest, the balsam woolly adelgid (A. piceae Rutze- ing the relevant pathways for a given pest. Nonetheless, burg), was also accidentally introduced in the latter part of human activities—particularly in the area of commercial the 20th century, and has removed more than 90 percent of trade—have received much attention for enabling the Fraser fir Abies( fraseri (Pursh) Poir.) from already sparsely spread of invasive pests. Human-mediated pest transport distributed spruce-fir communities in the southern Appa- is largely unintentional (Jenkins 1996): forest pests may lachians (Pimentel and others 2000). In a recent example, travel undetected on a variety of materials including wood the emerald ash borer (Agrilus plannipennis Fairmaire) now products, airline baggage, nursery plant stock, solid wood infests an estimated 40 000 km2 in the Great Lakes region packing materials, hikers’ clothing, and passenger vehicles and Ontario, where it has killed at least 15 million ash (Campbell 2001, Liebhold and others 2006, McCullough (Fraxinus spp.) trees and has regularly jumped quarantine and others 2006, Tkacz 2002, Work and others 2005). boundaries. It is likely that the insect was introduced to the In 2004, a joint workshop by the Society for Risk United States 10 or more years before it was first recog- Analysis Ecological Risk Assessment Specialty Group and nized in 2002, during which time populations were able to the Ecological Society of America Theoretical Ecology establish and spread undeterred (US-GAO 2006). Section focused on the standardization of methods for risk assessment as a component of a National Invasive Species Forest Pest Risk Assessments and Risk Maps Management Plan. Workshop participants noted a criti- Forest pest risk assessments are intended to provide forest cal need for data to represent pathways of introduction of managers with information to prepare for such situations, nonindigenous pests that are related to human trade and and in turn, reduce the number of invasive species that transport (Andersen and others 2004b). This information become harmful pests (Byers and others 2002). A risk need has been echoed by policymakers focused specifically assessment for a particular pest categorizes or quantifies its on forest pests (Chornesky and others 2005). For forest pest risk of introduction, establishment, spread if established, risk mapping, the challenge is threefold. First, the amount of and potential economic and environmental impacts (UN- spatial data specifically collected for forest pests is limited. FAO 1995). The spatial representation of such an assessment Second, it can be a challenge to apply available information is a map depicting the varying level of risk of introduction on pest biology and other fundamental characteristics to the or establishment of a pest throughout a geographic region of tasks of spatial data mining and interpretation, especially interest (Andersen and others 2004b). Risk maps facilitate since that fundamental information may be spread across early-detection/rapid-response procedures by providing a a wide range of journals, government documents, and 422 Advances in Threat Assessment and Their Application to Forest and Rangeland Management other literature (Ricciardi and others 2000). Finally, many For each of these categories, we discuss conceptual human-mediated pathways operate on broad (i.e., landscape, linkages between the available data and the depiction of regional, national, or even continental) spatial scales, forest pest introduction or spread risk. We describe some impeding their analysis. specific data sets