Dispersal

Dispersion pathways are a critical consideration in biotic forest threats management. Humans are the most important facilitator of forest pest introduction and spread. With expanding global trade and interstate commerce, the number of potential forest invaders is likely to rise. A fairly conservative projection suggests that international trade will result in the establishment of 120 nonnative insects and plant pathogens in the United States between 2000 and 2020 (Levine and D’Antonio 2003). For forest insects, the largest introduction risk seems to be associated with solid wood packing materials (Haack 2003, Haack 2006). Some of these materials may sit unattended in distribution facilities near ports of entry for weeks or more (Campbell 2001). Domestic commodity movement also expedites unnatural long-distance dispersion.

Biotic forest threats can be native or exotic, but their dispersion is principal in understanding how to limit risks. In this section, human-mediated pathways in forest pest risk mapping are discussed, including implication of imported products movement and several application examples.

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To review assessing landcover changes using aerial photography, consider reading the following Environmental Threats Case Studies:

Using Historical Photography to Monitor and Assess Threats over Time