theatlantic | The blight was first detected in June 2002, when the trees in Canton,
Michigan, got sick. The culprit, the emerald ash borer, had arrived
from overseas, and it rapidly spread -- a literal bug -- across state
and national lines to Ohio, Minnesota, Ontario. It popped up in more
distant, seemingly random locations as infested trees were unwittingly
shipped beyond the Midwest.
Within four years of first becoming infested, the ash trees die --
over 100 million since the plague began. In some cases, their death has
an immediate impact, as they fall on cars, houses, and people. In the
long term, their disappearance means parks and neighborhoods, once
tree-lined, are now bare.
Something else, less readily apparent, may have happened as well.
When the U.S. Forest Service looked at mortality rates in counties
affected by the emerald ash borer, they found increased mortality rates.
Specifically, more people were dying of cardiovascular and lower
respiratory tract illness -- the first and third most common causes of
death in the U.S. As the infestation took over
in each of these places, the connection to poor health strengthened.
The "relationship between trees and human health," as
they put it, is convincingly strong. They controlled for as many other demographic factors as possible. And yet, they are unable to satisfactorily explain why this might be so.
In a literal sense, of course, the absence of trees would mean the
near absence of oxygen -- on the most basic level, we cannot survive
without them. We
know, too, that trees act as a natural filter, cleaning the air from
pollutants, with measurable effects in urban areas. The Forest Service
put a 3.8 billion dollar value on the air pollution
annually removed by urban trees. In Washington D.C.,
trees remove nitrogen dioxide to an extent equivalent to
taking 274,000 cars off the traffic-packed beltway, saving an
estimated $51 million in annual pollution-related health care costs.
But a line of modern thought suggests that trees and other elements of
natural environments might affect our health in more nuanced ways as
well. Roger Ulrich demonstrated the power of having a connection with
nature, however tenous, in his classic 1984 study with patients
recovering from gall bladder removal surgery in a suburban Pennsylvania
hospital. He manipulated the view from the convalescents' windows so
that half were able to gaze at nature while the others saw only a brick
wall. Those with
trees outside their window recovered faster, and requested fewer
pain medications, than those with a "built" view. They even had slightly
fewer surgical complications.
