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Benefit-Cost Analysis
of Modesto’s Municipal Urban Forest. McPherson, G., R. Simpson, P. Peper, and
Q. Xiao. 1999. Journal of Arboriculture. 25(5):235-248. (Journal article)
A cost analysis may sound boring,
nevertheless this one is worthy of your time. This paper presents a
cost valuation of one of North America’s foremost tree cities, Modesto,
California, and the equation used can be applied to even the smallest
plot that might sustain a tree. Modesto supports approximately 90,000
trees with an annual planting/maintenance budget of $23,290
(1997-1998). The question addressed was, “Are these trees worth the
cost?”
Here’s what was discovered: annual
air pollution uptake is 154 metric tons (valued at $16 per tree).
Buildings that were shaded and had cooler temperatures saved 110,133
MBTU (valued at $10 per tree) and 13,900 tons of carbon dioxide were
sequestered by the trees (valued at $5 per tree). The value of a tree
directly increased with size. Larger trees have larger canopies with
more leaves and therefore transpire more water and sequester more
carbon. Other interesting findings were that monetary benefits varied
with the species; a larger tree having a greater value. Silver maples
and honey locusts had the greatest per tree value of $210 and $105
respectively; and they are fast-growing trees. Even though Modesto and
Portland have very different climates, the cost-benefit ratio shows
clearly that any city can benefit from a tree canopy.
Carbon Storage and
Sequestration by Urban Trees in the USA. Nowak, D. and D. Crane. March
2002. Environmental Pollution. 116(3):381-389. (Journal article)
Would you like to figure out how
many trees need to be planted to offset your vehicle use? Go to
http://www.resurgence.org/2005/howarth229.htm and use their carbon
calculator. This calculator, in combination with this journal article,
can assist in figuring what one needs in terms of urban tree cover.
With a lot of assumptions pertinent to Portland, we calculated roughly 4
trees per driving person if each has a car (considering size, age, and
number of trees). Large trees can store 1000 times more carbon than
small trees (Nowak, 1994), although forest sequestration rates are not
directly comparable to urban forests and stand structure is completely
different.
The Micrometeorology
of the Urban Forest. Oke, T. 1989. Philosophical Transactions of the
Royal Society of London, Series B, Biological Sciences.
324(1223):335-348. (Journal article)
If you are passionate about having
good air quality, this is the article for you. Observations of
atmospheric conditions and processes in cities provide the cornerstone
for advances in understanding urban climates and improving urban air
quality policies. This article scientifically documents the impact of
trees on air quality, such as lowering temperature and filtering
pollution. In addition, Oke identifies typical air layers found within
the urban canopy, which consists of irregular canopy layers, and an
urban heat island effect that produces turbulent air masses. These in
turn affect the movement of pollutants. This is a fascinating read.
Important tables and figures:
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Table 1: Scale and
classification of an urban tree canopy. This is a look at the
micrometeorological effects of various natural and building
structures in the city.
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Figure 1: Scheme of the daytime
energy exchanges between an isolated tree and its street
environment. This is a useful illustration showing energy inputs
and outputs.
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Figure 3: Distribution of
near-surface air temperature in the vicinity of urban parks.
The Effects of Urban
Trees on Air Quality. Nowak, D. 1995. USDA Forest Service. Syracuse,
NY.
www.fs.fed.us/ne/syracuse/gif/trees.pdf
More and more trees are being
planted in Portland (thanks to Friends of Trees and others) where
concrete and asphalt tend to be the norm of most cities. David Nowak,
guru of urban forests, assesses their effects, and writes of the
valuable jobs that trees perform once they are planted in a landscape
within the city. This article could be more appropriately titled,
“Everything you ever wanted to know about choosing the correct urban
tree to mitigate air pollution.” Beginning with the acronym TREE,
(Temperature reduction, Removal of air pollutants, Emission of VOCs and
Energy effects on buildings) Nowak writes that in general, air
temperature is reduced beneath trees, air pollutants are removed, gases
are absorbed and turned to non-harmful chemicals, carbon is sequestered,
ozone is reduced, particulate matter is captured, sulfur is reduced, and
so are nitrogen and nitrogen dioxide. This is a short, readable USDA
report, accessible online, that gives specific tree names, as well as
some tree offenders that give off VOCs.
Check the Weather in Any Part
of the Country. 2008.
www.wunderground.com
If, like us, you are curious about
the current weather in any part of the country, this is a nifty website
to visit. Type in any zip code and you can access the forecast for the
next five days. We mention it here because if you scroll down to the
bottom of the page you can find the current air quality and forecast for
the Portland area. Click even further to learn more about air pollution
in any area of the country. Very cool. One caveat; “America’s 25 Most
Ozone Polluted Cities” and “America’s Kid Friendly Cities” don’t seem to
jive statistically with each other. Plus, we wanted to know if the
ranking in the “Number of Bad Air Days” is over one year or over one
month. Still, it is interesting. | |
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