Domestic Commodity Movement Data

Human activity enhances the spread of many invasive pests by enabling long-distance dispersal beyond their natural abilities. For instance, insect eggs, larvae, and adults may be accidentally carried on cars or other vehicles, as has been the case with the range expansion of the gypsy moth (Lymantria dispar) in the Eastern United States (Marshall 1981). Perhaps more significantly, domestic shipments of commodities may carry undetected insects and pathogens from ports of entry to previously uninfested locations with favorable conditions. For example, research suggests that the normal spread of the emerald ash borer (Agrilus plannipennis) through local flights has been greatly exacerbated in the Great Lakes region by human transport of infested saplings or firewood (Muirhead and others 2006).

As with the international cargo data, a number of government agencies have developed data sets that track the flow of commercial freight via various transportation modes across the country. These databases may be categorized as either networked or non-networked in structure, depending on whether their focus is on the flow of commodity types or on an arc-node pattern for modeling a particular mode of transport (e.g., freight trucks). The user must consider attribute resolution (i.e., the level to which commodities are specified) and what this allows in terms of filtering and querying the data for application in forest pest risk maps.