“When Trees Die, People Die”

We often hear people say that a walk in the woods is restorative, but is there any scientific evidence of this relationship between nature and our mental and physical well-being?  Apparently there is.  Here are brief summaries of the many studies that found such a relationship:

  • Patients recovering from gall bladder surgery recovered faster in a room with a natural view than those with a view of a brick wall. (1)
  • Mortality—particularly from cardio-vascular illness—in England was found to be lower amongst those living in “green” environments (after controlling for socio-economic status). (2)
  • In Japan, a positive association was found between survival rate amongst seniors and access to walkable green space. (3)
  • In Holland, those living in greener areas were less likely to be diagnosed with 15 of the 24 health outcomes examined.  These results were strongest for anxiety and depression and for children. (4)
  • In New York City, children living in areas with more street trees were less likely to have asthma. (5)

Intervening variables probably influenced these outcomes.  For example, since trees reduce air pollution by absorbing many of the pollutants in the air, that is a probable explanation for reduced asthma rates where there are more trees. 

The survey of San Francisco’s urban forest conducted by the US Forest Service provides an estimate of how much pollution these trees are now removing from San Francisco’s air.  This survey estimates that there are 669,000 trees in San Francisco.  According to the survey, trees and shrubs in San Francisco are removing 260 tons of pollutants from the air every year:  “Pollution removal was greatest for particulate matter less than 10 microns (PM10), followed by ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO).”

The US Forest Service survey also informs us that San Francisco has one of the smallest tree canopies in the country, covering less than 12% of it’s land.  Only Newark, New Jersey has a slightly smaller tree canopy.  We should not be surprised by the small size of our urban forest.  It is an inhospitable climate for trees, which is why there were virtually no native trees in pre-settlement San Francisco.  If we want trees in San Francisco, most will be non-native trees that tolerate the harsh conditions.

The relationship between the death of trees and the death of people

Now there is a new study which found a statistical relationship between the death of millions of trees and increased death rates of people living in the vicinity of those trees:  “The Relationship between Trees and Human Health.”  (6)

White Ash or American Ash.  Creative Commons
White Ash or American Ash. Creative Commons

This study reports that there are 22 species of ash trees native in North America and 7.5 billion ash trees in the country.    In 2002, the emerald ash borer from East Asia was discovered in North America.  It was first seen in Detroit, Michigan and Windsor, Ontario.  Since its arrival, it is said to have killed 100 million ash trees.

The study estimated the correlation between emerald ash borer presence and county-level mortality from 1990 to 2007 in 15 US states while controlling for demographic variables.  The study found an increase in mortality related to cardiovascular and lower-respiratory-tract illness (pneumonia) in counties infested with emerald ash borer.  The relationship was stronger where the infestation of the emerald ash borer was greatest.  The study concluded that “Across the 15 states in the study area, the borer was associated with an additional 6113 deaths related to illness of the lower respiratory system, and 15,080 cardiovascular related deaths.”  

Atlantic magazine was impressed with these findings.  Shortly after the study was published, Atlantic informed their readers in an article entitled, “When Trees Die, People Die.”

Sticking our heads in the sand

Unfortunately, native plant advocates choose to ignore the valuable functions our trees perform in our environment, including how they remove pollutants from the air we breathe.  As we informed our readers recently, native plant advocates in San Francisco have convinced the University of California at San Francisco to destroy over 30,000 trees on their 61 acre open space reserve.  UCSF does not plan to replace most of these trees.

The Draft Environmental Impact Report for this project says nothing about the probable increase in air pollution resulting from this destruction.   In the legally mandated chapter regarding possible impact of the project on air quality, the Draft EIR speaks only of the fossil fuel pollution associated with the use of mechanized equipment needed to destroy these trees. 

The University of California at San Francisco is a medical institution.  It educates medical practitioners.  It provides patient care and it conducts medical research.  We find it deeply ironic that this medical institution would seemingly be unaware of the damage they will do to the health of its neighbors by destroying one of the few forests that exists in San Francisco.  Or worse, they are aware of the damage this project will do to the public’s health, but choose to hide it. 


Here are the things you can do to help us save this beautiful forest:

  • Sign the petition to save the forest.  Available here.
  • Attend and speak at a UCSF hearing about the project:  Monday, February 25, 2013, 7 pm, Millberry Union Conference Center, 500 Parnassus Ave, Golden Gate Room                                                                             
  • Submit a written public comment by 5 PM, March 19, 2013 to UCSF Environmental Coordinator Diane Wong at EIR@planning.ucsf.edu or mail to UCSF Campus Planning, Box 0286, San Francisco, CA 94143-0286.  Include your full name and address.
  • Write to the Board of Regents to ask why a public medical institution is engaging in such a controversial, expensive, and environmentally destructive act.  Address:   Office of the Secretary and Chief of Staff to the Regents,
1111 Franklin St., 12th Floor, Oakland, CA 94607
  Fax: (510) 987-9224
  • Subscribe to the website SaveSutro.com for ongoing information and analysis.


(1)    Ulrich, RS, “View through a window may influence recovery from surgery,” Science, 1984:224:420-421

(2)    Mitchell, R, Popham, F, “Effects of exposure to natural environment on health inequalities:  an observational study,” Lancet, 2008, 372:1655-1660

(3)    Takona, R., et. al., “Urban residential environments and senior citizens’ longevity in megacity areas,” J Epidemiol Community Health, 2002, 56(2):9013-918

(4)    Maas, J, et. al., “Morbidity is related to a green living environment,” J Epidemiol Community Health, 2009, 63(12):967-973

(5)    Lovasi, GS, et.al., “Children living in areas with more street trees have lower prevalence of asthma,” J Epidemoil Community Health, 2008, 62(7):647-649

(6)    Donavan, GH, et. al., “The Relationship between Trees and Human Health,” American Journal of Preventive Medicine, 2013, 44(2):139-145


3 thoughts on ““When Trees Die, People Die””

  1. Thank you for this informative article. We are fighting a similar fight in Santa Cruz, CA. The city council is poised to vote on a set of revisions to our Heritage Tree Ordinance which will weaken the Ordinance and remove blue gum eucalyptus from protection. No environmental review was done to assess the impact. Given the climate of hatred by some people for eucalyptus it is likely we will see the removal of hundreds of our remaining big trees. Folks somehow think Santa Cruz protects its big trees but according to city data, during a 5 year period, permits were granted to cut down 2,350 out of a possible 2,500 heritage trees. At this rate we will lose our urban forest within our lifetime. What human folly in a town which should know better.

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