By Mary L. Johnson and Deborah Boyer
Philadelphia, like many American cities, has a wealth of urban trees. Collectively known as the “urban forest,” these are the trees that line our city streets and river banks and adorn our urban parks and private lawns. Healthy trees improve the look and feel of city neighborhoods by providing shade and natural beauty, but they also provide valuable ecosystem services with a far-reaching impact on global climate change. Urban trees store millions of tons of carbon each year and slow the accumulation of greenhouse gases. Urban trees provide stormwater mitigation by intercepting rain on their leaf, branch and stem surfaces and by absorbing water through their roots. Urban trees improve air quality by lowering air temperatures and removing air pollutants through their leaves. A properly shaded urban neighborhood provides heat island mitigation in the summer and windbreak in the winter that can significantly reduce business and household energy consumption.
Managing and maintaining our urban forests provides clear environmental, economic and quality of life benefits. Such maintenance is more effective when there is an accurate and current inventory of all the trees in the municipal area. Having an up-to-date tree inventory enables organizations to better maintain the urban forest and plan future planting and renewal efforts. Creating an accurate inventory of urban trees, however, has been a difficult and time-consuming process for many municipalities. The responsible agencies are often under-funded and short-staffed, and their priorities are necessarily driven by weather damage, the impact of trees on electrical lines and other reactive activities. With limited resources and a long list of other necessary activities, how can a city or a region possibly find time to inventory every single tree?
Web-Based Urban Forestry Tools
Azavea is a geospatial software design and development firm based in Philadelphia. As a certified B Corporation whose mission is to apply geographic data and technology to creating sustainable, livable and vibrant communities, Azavea took on the challenge of designing a web-based solution that would help make the tree inventory process easier and more affordable for urban communities nationwide. The result is PhillyTreeMap.org, a wiki-inspired, web-based geography-enabled urban tree inventory application that serves as the prototype of a larger OpenTreeMap project. The goal of the OpenTreeMap project is to enable citizens, students and nonprofit organizations that are passionate about greening their communities to come together with local government agencies and other stakeholders in a joint effort to map, tend and preserve the urban forest.
PhillyTreeMap.org was developed using funding received from the USDA National Institute of Food and Agriculture as part of the Small Business Innovation Research Program (Grant Number 2010-33610-20937). The prototype was rolled out on April 29, 2011 – Arbor Day – as part of a Green Tech Showcase event held during Philly Tech Week.
The PhillyTreeMap prototype includes data for more than 177,000 trees within the larger thirteen-county, tri-state area surrounding the City of Philadelphia. The site can be searched by location, species, or more advanced criteria including diameter and date planted. Dropdown lists enable users to navigate quickly to a specific neighborhood of interest or explore only a particular species of tree. Each tree is represented by a marker on a large map with additional information available on a detailed profile page. The detail page for each tree provides an inset map of the tree’s geographic location as well as a street-level view of its surroundings as seen in Google Street View. The detail page also includes identifying information about each tree such as its species, height, diameter and overall health or condition.
While the site was populated initially with data sets from the Pennsylvania Horticultural Society, Philadelphia Parks & Recreation, and the Township of Lower Merion, public users can also edit the existing information or add new trees. To contribute to the inventory, users create a free account and then edit existing tree details, upload an image of a tree or add a new tree to the system. All changes are immediately visible on PhillyTreeMap, but a group of trained administrators also reviews the site for inaccurate or inappropriate entries.
PhillyTreeMap also generates estimates of the environmental impact of each tree on the urban environment. This includes stormwater interception, carbon sequestration, air quality and other metrics. The economic benefits are calculated using parameters generated by iTree, an urban forestry analysis and benefits assessment software suite developed by the USDA, and are automatically updated each time a tree is added or removed from the inventory. This is an important feature that could help municipalities justify their tree maintenance expenditures and determine the tree species best suited to targeted remediation tasks ranging from stormwater mitigation to air quality improvements to energy savings.
Ensuring the Integrity of the Data
Since the PhillyTreeMap user community consists of individuals with varying levels of horticultural experience, Azavea created several important features to make the inventory process easier to understand and keep the inventory data as accurate as possible. First, an integrated, region-specific Tree Key on the site guides users through the process of identifying a tree species, ensuring accurate information is entered into the database. The Tree Key provides images of leaves, flowers and other distinctive features that users can compare to an existing tree to help determine its species. An FAQ page provides important how-to information about the inventory process, including a helpful video tutorial on measuring tree trunk diameters.
Azavea also implemented a prototype “reputation” system and series of user levels. General users can add new trees and edit the majority of tree detail fields. Advanced users (often members of a horticultural group or trained arborists) can edit additional fields such as condition and height which require more experience to accurately assess. The reputation system enables users to accumulate points by adding trees and editing tree information. Advanced users can also express their opinion regarding the quality of an edit, which grants additional reputation points to the user who made the edit. General users who demonstrate a consistent pattern of accurate edits will accumulate “reputation points” that provide them with additional editing options on the site.
Other features provide additional data quality checks that reduce erroneous information. Those checks include flagging discrepancies in the height and diameter of a tree based on its species or the ratio between the diameter at breast height and the total height of a tree. Drop-down lists and autocomplete features require users to make selections based on selected lists. For example, PhillyTreeMap provides species restrictions that prohibit users from entering tree species that are not normally found in the area covered by the inventory.
A Collaborative Effort
From the beginning, collaboration has played an important role in the PhillyTreeMap project. Azavea partnered with Philadelphia Parks & Recreation, the Pennsylvania Horticultural Society (PHS), and the Delaware Valley Regional Planning Commission (DVRPC) to gain important design feedback throughout the iterative software development process. It was important for Azavea’s developers to understand what features these organizations thought were important in a wiki-inspired tree inventory application and what needed to be simplified or changed in order to make PhillyTreeMap as intuitive and user-friendly as possible.
Philadelphia Parks & Recreation, the Pennsylvania Horticultural Society and the Township of Lower Merion all contributed copies of their existing tree inventory data for inclusion in the PhillyTreeMap database, and will share the management and monitoring of the system. These data sets served as the start the tree mapping process. As part of rectifying multiple data sets, Azavea created methods for identifying and eliminating overlapping data points to prevent the entering of duplicate trees into the system. For example, PhillyTreeMap specifically flags those points which have a spatial proximity within the bounds of a pre-set parameter, such as within five feet of a documented existing tree. After some initial field testing and experimentation by its partner organizations, Azavea expanded this proximity from five to ten feet and included some additional provisions for data points originating from the same dataset. Implementing these changes enabled PhillyTreeMap to reduce the total overlap across all datasets to 0.69%.
The PhillyTreeMap website is built on open source code contributed by the Urban Forest Map project in San Francisco. Azavea was able to build upon this established foundation and add many new features, including the user reputation system, a redesigned Add-a-Tree page, customized user groups, support for several new data fields, redundancy checks to eliminate duplicate entries, a public commenting system, robust search capabilities, and a more flexible, data-driven Tree Key database that can be adapted to multiple locations. Azavea also integrated OpenLayers, an open source mapping library that enables PhillyTreeMap to support multiple base map options. These enhancements are being merged with the original Urban Forest Map code base and will be published as an open source project in mid- 2011.
Azavea and Urban Ecos, the group behind Urban Forest Map, continue to work together to update Urban Forest Map with the newly developed features from PhillyTreeMap as well as to roll out a new implementation for the Sacramento region. There has been interest from a number of communities both in the United States and internationally in using the project code to implement other similar systems. With limited resources available to many horticultural and municipal groups, this type of wiki-inspired map-based project can help organizations and governments collaborate with the public to create a useful and data-rich tree inventory. Just as the data collected by the decennial census is used to allocate billions of dollars in federal funds to local communities based on need, the data collected in a tree inventory can be used by communities to facilitate strategic decision-making policies and long-term resource allocations regarding the composition, condition, and distribution of the urban forest.