It’s a real pleasure to be here with colleagues from around the globe to talk about urban forests. As more people move to cities, urban forests are becoming increasingly important. In the United States, urban areas fill only about 3 percent of our land area but hold more than 80 percent of our citizens. Our urban and community forests cover about 40 million hectares and hold over 3.8 billion trees, with tremendous benefits for U.S. citizens. Trees make our cities more livable.
Benefits of Urban Forests
I’ll start with an example from Baltimore, Maryland, which is one of the oldest cities in United States and has more than 600,000 residents. It is known for its rich heritage, for its picturesque harbor, for its crab cakes … and for having some of the worst crime and poverty levels in the nation.
Scientists from the U.S. Forest Service Baltimore Field Station have teamed up with others to study how urban forests might help to reduce crimes in poor neighborhoods. After controlling for factors like income, population density, and housing type, the scientists found that increasing tree canopy density by 10 percent corresponded to a decrease in crime rates of about 12 percent.
We have seen similar results in Philadelphia, Pennsylvania. Scientists from our Philadelphia Field Station, working with partners, found less drug use and theft in areas with stormwater infrastructure improvements. Urban greening makes neighborhoods feel more pleasant, which builds a stronger sense of community and deters crime. When residents see improvements in their green spaces, they tend to come together to tackle neighborhood issues like crime.
So we know that trees can reduce crime and foster stronger communities. We also know that urban trees and green spaces can improve human health. Scientists have shown a strong correlation between urban forests and reduced levels of stress and obesity. Patients with views of green spaces heal faster.
Trees also improve air quality. One study showed that asthma rates decrease by 25 percent for every 340 trees planted per square kilometer. Forest Service scientists estimate that across the United States urban trees remove about 784,000 tons of pollutants each year. Without those trees, we would have to spend $3.8 billion each year to remove the same amount of air pollution.
Urban forests provide many essential ecosystem services … like removing air pollution … that make our cities more livable and that save money. For example, the shade from urban trees can cut as much as 30 percent of our summer electric cooling costs. Trees sequester carbon and abate noise. They help to protect urban water resources by filtering rain and snow and regulating stormwater runoff. They provide habitat for wildlife, such as squirrels, rabbits, and deer, but also birds of all kinds, including migratory species, and occasional predators like foxes and coyotes.
Urban trees are also good for business and property values. People prefer to shop and live on pleasant, shady streets. People are more likely to spend time outside in shady neighborhoods, where they can socialize with neighbors. Urban forests also create green jobs in arboriculture, landscaping, and other professions. One study of five U.S. cities has shown that every dollar invested in urban forest management returns up to three dollars in annual benefits.
Valuing Urban Forests
But the benefits from forests are often difficult to quantify because they have no recognized market value. Forests are at risk of being undervalued and lost, because our economic systems are set up to protect what has cash value and to take for granted what does not.
To avoid such market failures, researchers are measuring ecosystem services in economic terms. To help communities calculate the market value of their urban forests, the U.S. Forest Service developed a web-based tool known as i-Tree. i-Tree is a state-of-the-art, peer-reviewed software suite that you can download for free. i-Tree lets you find the dollar value of benefits from urban forests, including energy cost savings, stormwater capture, and city pollution absorption.
i-Tree was first released in 2006. Since then, i-Tree has been used in more than 100 countries and by about 12,000 users, and the information it provides has helped generate investments in municipal green spaces. Urban planners in Chattanooga, Tennessee, were able to show that for every dollar invested in their urban forests, the city received more than $12 in benefits. New York City used i-Tree to justify $220 million in spending to plant trees during the next decade.
Version 5 of i-Tree has just been released with many new features. For example, i-Tree can be used on more devices, including smartphones. It is also able to forecast the growth and benefits of trees over time, based on species and growth models specific to particular locations.
Connecting People to Nature
Investments in green infrastructure are important because urban forests and green spaces are where many people experience nature, enriching their lives. As Aldo Leopold once said, “the weeds in a city lot convey the same lessons as the redwoods.” People can see how an ecosystem works—how sun, soil, water, plants, animals, and people interact—along their local creek—along their neighborhood street—in their own backyard. By experiencing their urban forests and waters, people come to value them. And by valuing these resources, they are driven to protect and conserve the forests around them … and across the nation and the world.
At the U.S. Forest Service, we are working hard to deepen and strengthen connections between people and their forests. We have an array of programs designed to get people into the woods. Through our Conservation Education programs, for example, we reach more than 5 million people each year, many from urban areas. We often focus on children, who will be the next generations of environmental stewards, and on low-income communities with the least access to green spaces. In partnership with others, we are planting trees and establishing gardens in poor communities while offering jobs and youth development opportunities. We are working to give kids and their families places to play, to work, to grow healthy food, and to connect with their neighbors.
We are also offering professional development for teachers in inner cities, so that they can share the wonder and excitement of nature with their students. For example, through a partnership with the North American Monarch Institute, we have given hundreds of teachers in inner cities resources and training to engage students as they learn about and conserve monarch butterflies.
Here’s another example, this one from Amman, Jordan, where natural science curricula, resources, and tools are often limited. The U.S. Forest Service International Programs partnered with the Cell Motion Biobus from New York City and a local nongovernmental organization called the Princess Basma Youth Resource Center. Together, we created a mobile science and environment laboratory to encourage hands-on learning by youth in Amman and other parts of Jordan. Our seven-part conservation curriculum includes lessons on water, energy, and pollution and encourages youth to be active stewards and scientists. The project is led by two women scientist-instructors who reached over 12,000 kids last year, almost half of them refugees from neighboring countries.
A Living Continuum
At the U.S. Forest Service, we are making a strong case for increased investments in urban forests. We are giving people the science and tools they need to understand how crucial urban forests are to their health, wealth, and well-being. We are figuring out better and more effective ways to connect people to nature. And we are doing this work at home and across international borders. Under the FAO North American Forest Commission, we have started a new working group to look at urban forest programs and community outreach. Together, Canada, Mexico, and the United States are exploring ways to help cities reach out to communities, form citizen science projects, and attach market value to ecosystem services from urban forests.
But we have more to learn and more to do. The threats to rural forests—like drought, catastrophic wildfires, fragmentation and development, and outbreaks of forest pests and disease—also threaten urban forests. We need to protect our existing forests and create a more extensive and diverse urban tree canopy. And we need to maintain physical connections between rural and urban forests because our forests are like rivers: they are a living continuum connecting rural and urban landscapes across a nation.
I look forward to learning with you as we find the best ways to support and grow urban forests around the world. Thank you!