January 16, 2013. Evidence is increasing from multiple
scientific fields that exposure to the natural environment can
improve human health.
In a new study by the U.S. Forest Service, the presence of trees
was associated with human health.
For Geoffrey Donovan, a research
forester at the Forest Service’s
Pacific Northwest Research Station, and his colleagues, the loss
of 100 million trees in the eastern and midwestern United States
was an unprecedented opportunity to study the impact of a major change
in the natural environment on human health.
In an analysis of 18
years of data from 1,296 counties in 15 states, researchers found
that Americans living in areas infested by the
emerald ash borer, a beetle that kills ash trees, suffered from an
additional 15,000 deaths from cardiovascular disease and 6,000 more
deaths from lower respiratory disease when compared to uninfected
areas. When emerald ash borer comes into a community, city streets
lined with ash trees become treeless.
The researchers analyzed demographic,
human mortality, and forest health data at the county level between
1990 and 2007. The data came
from counties in states with at least one confirmed case of the emerald
ash borer in 2010. The findings—which hold true after accounting
for the influence of demographic differences, like income, race,
and education—are published in the current issue of the American
Journal of Preventive Medicine.
There’s a natural tendency to see our findings and conclude
that, surely, the higher mortality rates are because of some confounding
variable, like income or education, and not the loss of trees,” said
Donovan. “But we saw the same pattern repeated over and over
in counties with very different demographic makeups.”
the study shows the association between loss of trees and human
mortality from cardiovascular and lower respiratory disease,
it did not prove a causal link. The reason for the association
is yet to be determined.
The emerald ash borer was first discovered
near Detroit, Michigan, in 2002. The borer attacks all 22 species
of North American ash
and kills virtually all of the trees it infests.
The study was
conducted in collaboration with David Butry, with the National
Institute of Standards and Technology; Yvonne Michael,
Drexel University; and Jeffrey Prestemon, Andrew Liebhold, Demetrios
Gatziolis, and Megan Mao, with the Forest Service’s Southern,
Northern, and Pacific Northwest Research Stations.
A tree-lined street in Toledo, Ohio in 2006, before emerald ash borer
infestation. Credit: Dan Herms, Ohio State University
Three years later, in 2009, after the invasive insect spread to the neighborhood. Credit: Dan Herms, Ohio State University
Northwest Research Station—headquartered in Portland, Oregon—generates
and communicates scientific knowledge that helps people make informed
choices about natural resources and the environment. The station
has 11 laboratories and centers located in Alaska, Oregon, and
Washington and about 390 employees.