Can we forecast tree mortality? Predicting the next disease outbreak

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Original Paper:
Hudgins, E. J., Liebhold, A. M. and Leung, B. (2017), “Predicting the spread of all invasive forest pests in the United States.” Ecology Letters, 20: 426–435. DOI: 10.1111/ele.12741.

Tuesday, December 5, 2017

Pests have damaged U.S. forests for centuries. Globalization is increasing the spread of these pests and their danger to ecosystems. Now, new research models pest spread across landscapes using past data to better prepare for future threats.

Every disease has a story. The American elm tree has all but disappeared in the United States as the result of a pest. The fatal Dutch elm disease, originally brought to the U.S. by a small bark beetle hiding in wood shipped from the Netherlands to an Ohio furniture company, spread like wildfire. For more than 50 years Dutch elm swept across the continent, from Chicago to New York to Canada, eventually wiping out 75 percent of North America’s 77 million elms.

With rapid globalization, the movement of people and products is now commonplace. This leaves both humans and plants vulnerable to the spread of disease. While each disease has a different origin story, new research from McGill University and the U.S. Forest Service searches for commonalities that might help us predict and stop the next epidemic.

The study, led by Emma Hudgins at McGill and published in Ecology Letters, examines the spread of economically damaging forest pests —including all animals and plants that cause harm — in U.S. forests. Using a combination of initial pest detection points and mapping of current spread extent, the authors reconstructed spread patterns of damaging forest pests. The data-limited model also correlated this spread with human population density, forest cover, and life-history characteristics of the pests.

Modeling for travel distance, the researchers investigated if habitat, people, or pest characteristics impact where and how diseases spread. They modeled 75 different pest distributions using available data and life history traits of the pests.

Surprisingly, the study showed that characteristics of pests themselves have little influence on the spread of disease. Instead, the analysis showed that human population and the amount of forested land were the most important factors for predicting disease spread patterns. This result highlights the increasing influence of humans on the natural environment.

Scientists often do not know where or how the next pest or pathogen will strike. However, the use of general models can help predict more accurately where a disease might spread after it is introduced. There are limitations to this study, most notably that minimal data was available for the work. However, the commonalities in pest spread characteristics is a promising result and has resounding implications for humankind’s ability to combat forest pathogens.