American Forests: CITYgreen

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CITYgreen

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CITYgreen software conducts complex analyses of ecosystem services and creates easy-to-understand reports. The software calculates dollar benefits for the services provided by the trees and other green space in your specific area.

CITYgreen is GIS (Geographic Information System) software that is an extension to the ESRI’s (Environmental Systems Research Institute) ArcGIS. It works only with Windows-based PCs that have ArcGIS installed. It is not a stand-alone software package nor is it a tree inventory software application.

There are two versions of CITYgreen. One works with ArcView 3.x and the other with ArcGIS 8.x and later. These are not interchangeable. The most recent version works with ArcGIS 9.2 and also requires the Spatial Analyst extension from ESRI.

How does CITYgreen work?

CITYgreen analyzes the ecological and economic benefits of tree canopy and other green space. The analysis is based on a landcover dataset that is provided by the user. The source of the landcover dataset can be derived from a variety of sources, such as aerial photography or satellite imagery. The imagery should be leaf-on, color with a 4 meter or better resolution so all of the landcover features, such as individual trees, can be identified. The dataset must be ‘classified’ into various landcover features, such as tree canopy, open space, impervious surfaces, water, etc., before CITYgreen can analyze the data.

CITYgreen is not an image-processing application; although for small areas, users may heads-up digitize (draw) the landcover features directly tracing an aerial photo base map using the editing tools in ArcGIS. For larger areas, automated image processing tools are needed such as Erdas IMAGINE, eCognition or Feature Analyst.

What does CITYgreen do?

ALL versions of CITYgreen analyze the following:

Stormwater Runoff
	The stormwater model was developed by NRCS (Natural Resource Conservation Service, a division of USDA). Using this model, CITYgreen calculates the volume of runoff coming from the landcover based on a 2 year 24 hour rain event. More impervious surfaces generate higher levels of runoff, while more natural areas decrease the amount of runoff. This becomes a powerful modeling tool for planning and zoning. CITYgreen reports the runoff volume and dollar value associated with removing any excess stormwater resulting from changes in landcover, such as constructing a retention or detention pond.

Air Pollution Removal
	The air pollution model was developed by the US Forest Service and calculates the pollutant removal capacity of tree canopy. The results of the model show how much of five air pollutants the tree canopy is removing from the atmosphere. The greater the tree canopy, the more air pollution is removed. This is a useful tool when a community is trying to meet EPA air quality requirements. CITYgreen reports the annual quantity of pollutants removed and the dollar value associated with these services.

Carbon Storage and Sequestration
	This model was developed by the US Forest Service and calculates the amount of carbon stored in the trees represented on the landcover map and calculates the annual carbon removal by the trees.

Landcover Breakdown
	From the user-provided landcover map, CITYgreen reports the area for each landcover feature (impervious surface, tree canopy coverage, open space etc.). These areas are reported both as the actual number of acres and as a percentage of the total area. This is very useful when communities are establishing tree canopy goals or managing their land use.

Alternate Scenario Modeling
	One of the most powerful features of CITYgreen is the ability to analyze alternate scenarios. Starting with a current landcover map, the effects of future landcover change can be calculated before those changes are made. It is also useful to see how things have changed over time, by comparing landcover maps from earlier periods, such as 10 or 20 years ago. This becomes an important decision-making tool as communities are faced with growth and development choices.

How do the versions of CITYgreen differ?

Function	ArcGIS9.x	ArcView3.x

Air Pollution Removal Model	x	x
Carbon Storage Model	x	x
Carbon Sequestration Model	x	x
Stormwater Runoff Model	x	x
Water Quality Model	x
Tree Growth Model		x
Summer Energy Savings Model		x
Tree Attribute Table		x
Alternate Scenario Model	x	x
Landcover Breakdown	x	x

CITYgreen v.5 (ArcView 3.x) includes the following features:

Tree Attribute Table - This is the only version that has built-in functionality that allows a user to populate a tree attribute table. Field collected data on individual trees can be entered into this table. The table is useful in determining a variety of information, such as percentage by species, percentage by health, species location, etc. This table is the basis for the tree growth model. This is not a tree inventory management feature and does not include any functions for maintenance schedules. This feature makes CITYgreen v.5 ideal for educational purposes. See resources for educators.

Tree Growth Model – Using built-in tree growth coefficients and the information from the tree attribute table, CITYgreen can virtually grow the individual trees for any period up to 50 years in the future and will calculate the future ecological benefits of these individual trees.

Summer Energy Savings - This model requires a considerable amount of field collected data and local variables. Once the data collection is complete, the software calculates the energy savings for single family homes base on the location and shade characteristics of the trees around the home. Because of the amount of data needed, this feature is not often used and was eliminated from later versions of the software.

CITYgreen for ArcGIS (ArcGIS 8.x/9.x) includes the following features:

Water Quality – This model was developed by Purdue University. Called the L-THIA (Long-Term Hydrologic Impact Assessment) tool, it uses the NRCS data to determine the average amount of several non-point source pollutants in stormwater runoff. As runoff increases, the pollutant loading also increases. This is very useful for communities that are striving to meet clean water requirements.

Why the functional differences in the versions?

CITYgreen for ArcGIS (ArcGIS 8.x/9.x) was developed with the GIS professional in mind. It is a raster-based analysis application and, as such, trees are treated as a landcover feature in the same way as other landcover features such as water, open space, etc. Therefore, trees are considered as one component of an ecosystem rather than as individual trees. Since all of the components interact, a change to one component affects the overall ecological benefits of the entire area. It is also because of this treatment of trees, that analysis of ecosystems cannot be performed on a tree-by-tree basis.

International Clients

The data contained in CITYgreen is based on research conducted in the United States. This includes data for soil types (US Department of Agriculture); rainfall data (National Oceanic and Atmospheric Administration); air pollution removal data (US Forests Service); carbon storage and sequestration (US Forest Service); stormwater runoff data (National Resource Conservation Service).

Because all of the data contained within CITYgreen is based on the US, CITYgreen is not recommended for use in other countries.

Pricing, Ordering and Discounts (See Pricing at a Glance)

ASLA Member Discount

ASLA members receive a $200 discount off the commercial or government purchase price of CITYgreen. On the order form, indicate (ASLA/MBR) and your ASLA number on the membership line. Select the “group purchase” price on the order form.