Why urban forests? San Diego faces its green heritage

A healthy urban forest in San Diego can conserve energy

Our grandparents, lacking the modern day creature comforts of central heating and air conditioning, used trees to modify and regulate the climates of their homes; and with far less environmental damage than today's modern conveniences (Weather-Wise Gardening; Ortho Books; 1974,1978; pg.3

Incontrovertible, scientific studies prove that trees in communities do this. Here's how:

Shading, which reduces the amount of radiant energy absorbed and stored by built surfaces.

Evapotranspiration, which converts liquid water in leaves to vapor, thereby cooling the air.

Reducing the velocity of wind, which slows the infiltration of outside air into inside spaces.

Trees planted in large quantities in a carefully planned and scientific manner in cities are the most cost-effective tool a city can employ to mitigate what scientists refer to as the Urban Heat Island (UHI) phenomenon. Scientists studying this phenomenon believe that billions of dollars are spent each year just to compensate for the increased heat of an Urban Heat Island.

Chicago's UHI played a role in the many deaths in that city during a heat wave in the early 90s. Their mitigation, primarily focused on tree planting, revealed these interesting results:

• Air Quality benefits in 1991 worth $9.2 million.
  
• Carbon sequestration = 155,000 tons/year, helping to reduce the greenhouse effect and global warming. They also reduce building energy use for heating and cooling, which in turn reduces carbon emissions from power plants by about 12,600 tons/year.
  
• Large trees remove 60 to 70 times more pollution and store up to 1000 times more carbon than small trees.
  
• Although street trees account for only 10% of the city's trees, they make up 24% of total leaf surface area because they are older and larger than off-street trees.
  
• Trees provide net benefits worth 2 to 3 times the cost of planting and caring for them over a 30-year period.
  
• Greatest savings for energy, air quality and water were derived from residential tree plantings, closely followed by street tree plantings.
  

In addition to the demonstrated energy/air quality/water benefits provided by a thriving urban forest, there are ancillary benefits as well, which include:

• Noise reduction
  
• Wildlife habitat
  
• Reduce surface runoff and protect urban water
  
• Enhance the aesthetic quality of life in the city; create feelings of relaxation and well-being; provide privacy and a sense of solitude and security.
  
• Increase property values.
  
• Increase economic stability by attracting business and tourists.
  
• Reduce glare (indirect health benefits: cataracts and skin cancer)
  

These benefits appear to directly or indirectly address additional goals of San Diego's Mayor Murphy:

#3: Create neighborhoods we can be proud of (direct).

#4: Clean up our beaches and bays (direct).

#2: Reduce traffic congestion (indirect, by making communities more pedestrian-friendly).

#8: Make San Diego America's safest city (trees' calming effect: the City of Irvine claims it is the safest city and they have lots and lots of trees - your call on direct/indirect).

#10: Complete MSCP open space acquisitions (indirect, habitat: large trees provide nesting spaces; small trees roosting spaces.).

During the OPEC energy crisis of the 1970s, the California legislature passed a bill titled: “The Urban Forestry Act of 1978” (Ca. Public Resources Code Sect. 4799.o6 - 4799.12) which declared city trees to be energy conserving “valuable economic assets” to cities. More recently, in 1993, based upon more research, the California legislature passed Government Code 53067, which states: “As canopy cover increases the public benefits increase.”

Like all major metropolitan cities in the United States, San Diego has been losing its urban forest at alarming rates over the past 25 years.

In 1993, People For Trees, with assistance from SANDAG, prepared a State of the Urban Forest report for the San Diego Region. In this report one learns:

“The City of San Diego has the largest tree care budget, but no planting budget...1968 was the last year money was budgeted for new street tree plantings and 1974 was the last year any funds were budgeted for replacement street trees.”

Also reported, as of 1993:
“...An additional 934,000 street trees would need to be planted to meet the national standard [US Park and Recreation] of 200 street trees per mile for our 7,024 miles of streets.”

Sadly, we learn that San Diego's canopy cover in 1993 was, at best, only 19% of this standard, while a minimum of 40% overall is the recommended percentage. Further:

“Tree removals continue and have recently ranged from 300 to 500 annually.”

That was in October 1993. Monthly tree removal lists from the City's Street Division for District Six for the recent several years reveal that District Six is losing anywhere from 200 to 300 trees annually, all by itself!

Conclusion
Urban Heat Islands endanger the public, both physically and fiscally. Implementation of the “Cool Communities” mitigation measures recommended by the experts and presented here today would set the City of San Diego on an appropriate course of action for providing healthy ecosystems and communities