(From a PowerPoint presentation developed by Greg Johnson, MDNR Forester)



PURIFY AIR & Combat the Greenhouse Effect


  • There is up to a 60% reduction in street level particulates (small particles, <10 microns, emitted in smoke from burning fuel, particularly diesel, that enters out lungs and cause respiratory problems.
  • Trees remove sulfur dioxide and nitrogen oxide, two major components of acid rain and ozone pollution, from the air.
  • One sugar maple (12" DBH) along a roadway removes in one growing season 60mg cadmium, 140 mg chromium, 820 mg nickel, and 5200 mg lead from the environment.
  • A total of 300 trees can counter balance the amount of pollution one person produces in a lifetime.
  • Global warming is the result of an excess of greenhouse gases, created by burning fossil fuels and destroying tropical rainforests. Heat from the sun, reflected back from the earth, is trapped in this thickening layer of gases and global temperatures rise as a result. About half of the greenhouse effect is caused by Carbon dioxide (CO2).
  • Current CO2 level of our atmosphere is 27% greater than at any time during the last 650,000 years.
  • Trees remove CO2 from our atmosphere - utilizing carbon to manufacture food and releasing oxygen as a by-product. On average, a single tree removes 226 to 911 pounds of carbon dioxide per year, and releases enough oxygen back into the atmosphere to support 2 human beings.




  • Forests are consistently at least 2 to 4 degrees cooler during the summer and 1 to 2 degrees warmer during the winter than open lands.
  • Without tree cover, streets and parking lots can raise air temperatures as much as 35 degrees. Such "heat islands" can cause cities to be five to nine degrees warmer than surrounding areas.






  • Soil erosion is reduced by the interception of rainfall by leafy crowns, and stabilization of soil by extensive root systems. A typical 20-year-old hackberry intercepts 1,394 gallons of rainfall per year.  After 40 years, this figure increases to 5,387 gallons per year.
  • Trees remove subsurface water (containing nitrates and other contaminates) before water runs off to storm basins and rivers.  Contaminants are transformed and stored inside of trees.
  • Water infiltration rates for forested areas are 1015 times greater than for equivalent areas of turf and grass, so more water stays on the land.
  • Soil conditions beneath trees encourage the growth of microbes that are efficient in transforming harmful chemicals into non-toxic forms.
  • Trees absorb stormwater that might otherwise result in flash flooding.  A city's urban forest can reduce peak storm runoff by 10 to 20 percent. For every 5% of tree cover added to a community, stormwater runoff is reduced by approximately 2%. 


  • Trees provide homes and a source of food for animals that would otherwise be unable to survive in an urban habitat.



  • Studies have identified a direct correlation between the amount of trees and grass in community common spaces and the use of those common spaces by residents, which leads to more opportunities for informal social interaction and greater relationships between neighbors.
  • Trees have the potential to reduce social service budgets, decrease police calls for domestic violence, strengthen urban communities, and decrease the incidence of child abuse according to the study.  (Chicago recently spent $10 million to plant 20,000 trees, a decision influenced by increased social benefits).
  • Researchers found fewer reports of physical violence in homes that had trees outside the buildings. Of the residents interviewed, 14% of residents living in barren conditions have threatened to use a knife or gun against their children versus 3% for the residents living in green conditions.
  • Trees make communities livable for people and soften the outline of concrete, masonry, metal and glass.
  • Trees can be associated with specific places, such as memories of past events or times, or a favorite tree climbed as a youth.



  • Studies have found a correlation between community forests and the average amount of physical activity exerted by neighborhood residents. People are more inclined to be outdoors and exercise when their surroundings are greener.  Logically, greater physical activity leads to fewer cases of obesity, which in turn may help reduce other health problems such as heart disease and diabetes.
  • Children who spend more time outside pay better attention inside.  Attention‑deficit/hyperactivity disorder (ADHD) children, in particular, are better able to concentrate, complete tasks, and follow directions after playing in natural settings.
  • Trees filter airborne pollutants and can reduce the conditions that cause asthma; asthma incidents increase in urban communities where trees are eliminated in favor of new roads, homes or commercial developments.
  • Trees relieve psychological stresses, helping to create a sense of relaxation and well being.  Studies have shown that hospital patients recovering from surgery in a room with a view of trees reportedly required fewer strong pain relievers, experienced fewer complications, and were released from the hospital sooner than those without a tree view.
  • According to a National Skin Cancer Prevention Education Program report released in 1996 by the Centers for Disease Control and Prevention, skin cancer is the most common and most rapidly increasing form of cancer in the country. Trees provide protection from cancer-causing ultra-violet rays, especially on campuses and in playgrounds where children spend hours outdoors.



  • Trees add color, texture, line, and form to our landscape.  Research on the aesthetic quality of residential streets shows that street trees are the single strongest positive influence on scenic quality.
  • The scope and condition of a community's trees and, collectively, its urban forest, is usually the first impression a community projects to its visitors. A community's urban forest is an extension of its pride and community spirit.
  • Studies have shown that: Trees enhance community economic stability by attracting businesses, shoppers, and tourists.  People are willing to shop longer and more often, pay more for parking, and pay up to 11% more for goods and services in well-landscaped business districts. 
  • In a survey of one southern community, 74% of the public preferred to patronize commercial establishments whose structures and parking lots are beautified with trees and other landscaping.
  • Consumer product testing in shopping areas with large numbers of shade trees were rated 30 percent higher than identical products rated in shopping areas that were barren of trees.









  • A 100 foot wide and 45-foot tall patch of trees can reduce noise levels by 50 percent.  Plants also absorb more high frequency noise than low frequency noise, which is most distressing to people.
  • Trees can mask concrete walls or parking lots, and power lines and poles – creating an eye-soothing canopy of green.




  • Depending on species and location, a single city tree in southern or central Minnesota can be expected to generate a net benefit— after the expense of planting, maintenance, and removal are subtracted—of $160 to $3,040 during a 40-year period. The benefit calculations include energy savings, increased property value, reduced storm-water runoff, improved air quality, and carbon dioxide reduction.


Average annual net benefits per tree for a 40-year-old tree:




$3 (public prop.) to $15 (private yard)


                                                                                         MEDIUM TREE

$4 (public prop.) to $34 (private yard)



$58 (public prop.) to $76 (private yard)

Yard trees produce higher net benefits than public trees, primarily because of lower home maintenance costs.
  • USFS researchers found that nearly 200,000 public trees in Minneapolis provide a total gross annual benefit of $24.9 million in energy savings, carbon dioxide emission reductions, air pollution reduction, storm-water management, aesthetics, and enhanced property values. After the costs associated with trees are subtracted, the net benefit averages out citywide to $15.7 million, or $79 per tree per year.