:: Methodology ::

:: CITYgreen Samples :: UFORE Samples ::

To estimate the services and value of an urban forest site, the software extrapolates from established research findings and calculations, which can be very comprehensive and applicable and have been tested by foresters and other scientists. Economist calculations for externality costs were also used. However, this cookbook approach also has its problems (see critiques). For example, in some cases where local data is not available, estimates will be based on data taken from a similar region-- this may yield incorrect results. However as more data from different parts of the country and world is collected and software is updates, these estimates will likely become more and more accurate.

The following shows examples of some of the methods that each application uses to calculate forest services and value. Unless otherwise noted, this information is drawn directly from the UFORE methodology and CITYgreen's user manual. More detailed accounts can be found there, as well as the references used to develop the models.

CITYgreen 5.0 -- drawn from CITYgreen 5.0 manual (contact American Forests for manual)

Pollutant Removal -- This is based on UFORE modeling

The program estimates the amount of pollution being deposited within a certain
given study site based on pollution data from the nearest city then estimates the
removal rate based on the area of tree and/or forest canopy coverage on the site.

The methodology determines a pollutant removal rate, or flux (F), by multiplying
the deposition velocity (V d) by the pollution concentration (C).

F (g/cm2/sec) = V d(cm/sec) x C (g/cm3)

The pollutant flux is then multiplied by the size of the area during periods in which
the pollutant is known to exist there. This makes it possible to estimate the total pol-
lutant flux for that surface by the hour. Hourly fluxes can be summed to estimate
daily, monthly, or yearly fluxes.

Carbon Storage and Sequestration -- This is based on UFORE modeling

CITYgreen’s carbon module quantifies the role of urban forests in removing atmos-
pheric carbon dioxide and storing the carbon. Based on tree attribute data on trunk
diameter, CITYgreen estimates the age distribution of trees within a given site and
assigns one of three Age Distribution Types. Type I represents a distribution of com-
paratively young trees. Type 2 represents a distribution of older trees. Type 3
describes a site with a balanced distribution of ages. Sites with older trees (with more
biomass) are assumed to remove more carbon than those with younger trees (less
biomass) and other species. For forest patches, CITYgreen relies on attribute data on
the dominant diameter class to calculate carbon benefits.

Each distribution type is associated with a multiplier, which is combined with the
overall size of the site and the site’s canopy coverage to estimate how much carbon is
removed from a given site....CITYgreen uses these multipliers to estimate carbon storage capacity and carbon sequestration rates. For example, to estimate carbon storage in a study area:

Study area (acres) x Percent tree cover x Carbon Storage Multiplier = Carbon Storage
Capacity

To estimate carbon sequestration:

Study area (acres) x Percent tree cover x Carbon Sequestration Multiplier = Carbon
Sequestration Annual Rate