As tree-planting efforts take root in cities around the world, urban managers turn to geospatial tools to map and monitor their community’s canopy cover.
New Yorkers are fast walkers. But there are those who prefer to take it slow, like the group of well-trained volunteers who purposely roamed around the streets of the Big Apple, stopping at each tree to meticulously measure their girth, and then recording them on a specially designed web mapping application. Each step helps take care of the city’s 800,000-plus arboreal dwellers.
Since 2015, thousands of participants have taken part in the city’s Street Tree Census, which according to the Department of Parks and Recreation of New York City (NYC Parks), is the largest community-led municipal urban forestry project in United States history. Equipped with survey wheels, tape measures, and a booklet for tree identification, the citizen volunteers collected tree-related data (species, diameter, health status, location) and logged them in a website that was particularly created for the mapping project.
The green streets of New York City.
The NYC Parks continued the inventory until 2018 in order to include not just trees that line the streets, but also those that thrive in the city’s parks. Around 40 percent of the city’s “green space” includes parks, cemeteries, and back yards, according to a separate study by Yale University.
Yet despite the important role that they play in the well-being of New Yorkers, trees are often overshadowed by the city’s concrete buildings and steel skyscrapers.
“Our New York City trees provide countless benefits to the city and residents,” said Meera Joshi, deputy mayor for operations. “They provide the air we breathe, help to keep temperatures down, and manage flood waters.”
Living Tree Map
Just before Christmas last year, the NYC Parks launched the NYC Tree Map (https://tree-map.nycgovparks.org), a website that allows anyone to “digitally interact” with all the trees in the city’s landscaped parks and streets in real-time. Billed as the “first-of-its-kind living tree map,” the NYC Tree Map is a repository of all the individually managed trees in the Big Apple. Using the website, concerned citizens can report any tree that they deem unhealthy, follow up the inspections, and monitor tree-related activities on the map, all in real time.
Interface of the New York City Tree Map.
“Our new NYC Tree Map is groundbreaking,” said NYC Parks commissioner Sue Donoghue. “With a slate of new features, we hope this new map will empower New Yorkers to visit their local parks, find their trees, and learn about the wonderful benefits our trees offer our communities.”
This tree map is data-driven and has its origins from the previous work of NYC Parks with TreeKIT, a community-led initiative that helps city dwellers to “measure, map, and collaboratively manage their urban forests.” Philip Silva, an environmental planner, co-founded TreeKIT with Liz Barry, a landscape architect who has a knack for creating geographic tools and civic science methods.
“New York City Parks heavily rely on volunteers to take care of street trees,” said Silva in a separate interview with DNAinfo. “So, we made maps in order to help volunteers track their work and see where their help can be most effective.”
To reach their goal of mapping the trees of New York, TreeKIT worked with several mapping companies, including CartoDB, in order to develop and test prototypes of a mobile data entry tool that will streamline the tree plotting process. Azavea, a geospatial software company based in Philadelphia and creator of the popular OpenTreeMap platform, improved the mobile collection app and web site of TreeKIT.
Since their collaboration with NYC Parks, the tree mapping work that TreeKIT started has been replicated in other U.S. cities such as Philadelphia, Seattle, and in Washington D.C.
Web mapping interface of Washington DC’s 165,000 public trees.
In the country’s capital, for example, the D.C.’s Urban Forestry Division has collaborated with the National Parks Service and Casey Trees, a nonprofit, to map the city’s famous cherry trees and track their flowering period. This map helps guide both citizens and visitors to areas where they can view the cherry trees in full bloom. It was built using the same tree inventory data gathered by both the staff of the said organizations as well as volunteers who measured and identified each and every tree that they encountered in the city.
Seeing the woods for the trees
Yet aside from manual surveys and footwork, D.C.’s Urban Forestry Division is also banking on more advanced geospatial technologies to monitor not just cherry trees, but all of the capital’s green canopy.
Street-level imagery and lidar point cloud data are all stored in the division’s geographic information system (GIS) database to provide its planners with highly accurate location data plus reliable height and crown canopy information for every single one of the capital’s public trees. The trees, all 175,000 of them and counting, can be accessed using the ArcGIS online platform https://dcgis.maps.arcgis.com.
There are generally two main techniques to quantify tree cover in urban areas. One is through ground-based field visits, as in the case of New York’s Street Tree Census, and another is via the use of remote sensing tools, as with D.C.’s lidar and photo-interpretation of urban tree imagery. The former is relatively cheaper to conduct compared to the latter, and takes longer to complete.
However, ground-based assessments have the advantage of capturing the nitty-gritty details of the city’s forest composition, from each tree’s species name, down to their health condition. For cities where budget is not an issue, combining both ground and remotely sensed techniques can lead to better tree inventories because imagery-based tree cover maps can provide information on both the area of tree coverage as well as the trees’ exact spatial locations.
That’s the path that Chicago has chosen, going even further with mapping by combining its own lidar data of tree canopy with additional information related to the air quality, surface temperature, and traffic volume of the city’s neighborhoods. The aim of the city’s Department of Public Health is to build and use an advanced mapping tool, developed together with the University of Chicago, to help improve the health of communities.
A study conducted by a team of University of Chicago researchers, found that more trees were associated with a range of positive environmental outcomes, including better air quality and lower summer surface temperatures. Hence the city’s urban planners are now planning to use the location-based information from this new mapping tool to help guide the city’s tree planting program. Their plan is to establish roughly 75,000 new trees over the next five years in areas with lower tree canopy covers.
“Trees are the most advanced and the most natural form of technology we have to combat climate change. We know that they can reduce heat, they can improve air quality, and they can help manage storm water,” said Gaby Wagener-Sobrero, environmental policy analyst at the Chicago mayor’s office, in an interview with ABC 7 news.
No beating around the bush
In Europe, urban planners are using a set of different tools to measure and map the trees in their cities. Copernicus, the space program run by the European Union (EU) and European Space Agency (ESA), is helping urban areas stay green with the aid of a fleet of Earth-observing satellites called Sentinel. For example, the Sentinel-2 satellite is being used by geospatial professionals to delineate and classify urban forests up to a spatial resolution of 10m. At that level of detail, useful urban atlas maps have been created for every EU-member country. And that atlas includes the maps of streets with trees, which can be freely accessed on the Copernicus Land Monitoring Service website (https://land.copernicus.eu).
The beautiful Italian city of Naples, for example, is harnessing this satellite-derived tree-mapping data to tackle climate change. The importance of maintaining tree cover is vital for Naples where the Mediterranean climate produces extremely hot and dry summers. Researchers there have used the urban tree satellite imagery, as captured remotely by Sentinel satellites, and combined them with i-Tree Cool Air, a computer model designed by U.S. scientists that can estimate the benefits of tree canopies in cities, such as the amount of air pollution removed and reduction in air temperature.
Results of their rigorous simulations have shown that a 10 percent increase in tree cover in Naples can cool temperatures by 0.2°C. That’s enough to create a 5°C difference in air temperature between urban areas with trees versus those with only impervious surfaces, such as concrete and asphalt.
While most cities create flat two-dimensional maps of their urban trees, Singapore has decided to go full 3D. The country’s National Parks Board, the main government agency tasked to take care of Singapore’s six million trees, is using various three-dimensional spatial data capturing tools so that their arborists can monitor each tree at a click of a button. It has collaborated with the geospatial company Greehill whose in-house technology is harnessing the power of remote sensing and artificial intelligence to help cities manage their urban forestry management through digitization.
Using Greehill’s car-mounted lidar scanners and 360-degree cameras, the National Parks Board can safely collect data on more than 10,000 trees in a single day. Artificial intelligence algorithms then crunch these point-cloud data of the urban environment to create a “digital twin” of every tree in the city, including the trees’ height, leaf area, and general health condition.
“This [method] actually takes away the manual efforts so that our staff doesn’t have to go around to measure all the trees. This can now be done automatically,” said Tan Chong Lee, CEO of the National Parks Board, in an interview with The Register.
With all the 3D data points collected from the urban greenery of Singapore, the city now has a digital twin of its tree dwellers, which can be viewed in this Mapbox-based interactive map (https://exploretrees.sg). Try to click on any 3D avatar of any tree in the map and you will find its Latin name and important arboreal measurements (girth, height, and age).
Shake one’s tree
As in Singapore, and in many cities around the world, the impacts of climate change, in particular the urban heat island effect, have prompted huge government backing to plant trees in urban areas.
In the U.S., for instance, federal support to the Healthy Streets Program will be able to help cities expand their tree cover to help tackle extreme heat, poor air quality, and floods. While in Europe, its Green Deal program is committing to plant at least three billion additional trees by 2030. They are using a mapping platform, MapMyTree, to check on the program’s progress.
However, even as urban greening programs accelerate around the world, cities still face a growing list of challenges. Obtaining lands to plant trees remains limited, resulting in stiff competition for space with the expansion of roads and construction of new buildings. And as both developers and urbanites worldwide compete for water and remaining city spaces, they also drive up costs for maintaining urban forests. In the U.S., keeping a healthy green urban cover is estimated to cost from $12.87 to $65 per tree, according to one study.
Costs aside, New York City remains enthusiastic to plant more trees. There were 13,000 new trees planted in 2022, and city officials are ready to shell out more green cash. They have already allocated $112 million to grow more trees.
“As climate change advances, trees and our city’s green spaces are becoming even more critical infrastructure that will pay dividends for generations to come,” said New York City Mayor Eric Adams.
The famous cherry trees of Washington D.C.
Turn over a new leaf
Yet another important issue to increasing urban greening projects is location. While cities focus mainly on counting the number of trees planted, most forget that rooting them in areas where they can survive and where they are most needed are just as crucial. In New York, high tree mortality rates have been documented where tree deaths reached up to 22 percent of the total seedlings planted during previous urban greening campaigns.
“Where the next generation of street trees are planted is as important as how many are planted,” said J. Meejin Yoon, dean of the College of Architecture, Art, and Planning at Cornell University, in a statement.
Again, geospatial tools can address this challenge. Yoon and her team of researchers at the Cornell Design Across Scales Lab have developed a spatial data visualization tool that maps urban data sets and lidar scans of trees in New York to guide future tree planting projects and move past efforts that simply count the number of trees planted.
“Individual trees have highly local impacts, including shading buildings, sidewalks, and public spaces and improving air quality along high-traffic streets,” she said. “Developing modern tools to study these impacts and planting [trees] based on equity and effectiveness is vital to a city’s future.”