Representing Human-Mediated Pathways in Forest Pest Risk Mapping

Frank H. Koch and William D. Smith

North Carolina State University Department of Forestry and Environmental Resources and USDA Forest Service Southern Research Station

Historically, U.S. forests have been invaded by a variety of non-indigenous insects and pathogens.  Some of these pests have catastrophically impacted important species over a relatively short time frame.  For example, the once-dominant American chestnut (Castanea dentata) was virtually eliminated from eastern U.S. forests by chestnut blight (Cryphonectria parasitica) within fifty years of the pathogen’s introduction from Asia.  To curtail future changes of this magnitude, agencies such as the USDA Forest Service have devoted substantial resources to assess the risks associated with recent or potential forest invaders.  These assessments of risk typically include a mapping component; among other things, this presents a useful way to organize early-detection/rapid-response procedures.  However, much forest pest risk mapping work has been limited to readily available and manageable data sets, which results in representations of risk that heavily favor climatic factors or estimates of host species distribution.  Detailed examinations of specific pathways of spread are often neglected in forest pest risk analyses due to a lack of spatial data or uncertainty about a pest’s predictive model parameters.

Humans are increasingly the most important facilitator of forest pest introduction and spread, even at the landscape level.  Moreover, with expanding global trade and interstate commerce, the number of potential forest invaders is likely to rise, making the analysis of human-mediated pathways particularly timely.  In this synthesis, we present a number of spatial data sources that can be utilized to represent these human-mediated pathways.  Collected by federal agencies and private companies for a range of purposes, these data sets can be manipulated to represent forest pest risks either directly or indirectly.  Although general in nature, queries can often be used to tailor these data sets to address specific pests.  Perhaps most importantly, the source data can usually be acquired for free or at negligible cost.

Using the sudden oak death pathogen (Phytophthora ramorum) and other pests as examples, we illustrate how some of these data sources can be used for mapping risks associated with human-mediated pathways.  First, we demonstrate the use of foreign import cargo statistics, both marine and airborne, to assess the risk of introduction of new species at U.S. ports of entry.  In particular, we show how information on shipments of high-risk commodities from countries of concern can be combined with pest interception data to rank ports according to their risk of introducing specific pest species. Second, we utilize inland waterway cargo statistics, freight analysis networks, and other databases on interstate commodity traffic to map regional and local spread of forest pests.  Third, we explain the diverse applications of business location databases, not only to identify clusters of high-risk businesses, but also to rank these businesses using a suite of socioeconomic factors.  Finally, we discuss the limited availability of up-to-date land cover/land use data, and present alternative data sources for representing high-risk areas of urbanization as well as the wildland-urban interface. 

While many of these data sets are imperfect depictions of human-mediated pathways, integration of several can add significant depth to early-detection/rapid-response projects.  For instance, they can be used in conjunction with up-to-date climate and host species data to yield refined epidemiological maps, and as backdrops for simulated forest pest introductions.  Furthermore, many of these data sets are applicable for forest threats other than pests.  To facilitate further applications, we discuss current limitations, future information needs, and potential sources of additional data regarding human-mediated pathways. 

Exotic Pests Session - Tuesday Afternoon

corresponding author:

Frank H. Koch
Department of Forestry and Environmental Resources
North Carolina State University
2028 Biltmore Hall
Campus Box 8001
Raleigh, NC 27695
919-549-4006
fkoch@fs.fed.us