The MacArthur ‘Genius’ Changing How We Think About Urban Trees

When it comes to cities, we know that planting trees will help urbanites endure the climate crisis by creating shade while photosynthesis can cool the atmosphere. But what many city planners and scientists have trouble implementing are cost-efficient and effective climate mitigation strategies. Many look to trees as an ideal solution, but even that’s proven hard to implement. In 2007, the City of Boston announced its plan to plant 100,000 trees in 10 years, but struggled to keep newly planted trees alive and ultimately failed to meet its goal.

Since then, the climate crisis has only gotten worse with record breaking global summer temperatures and dangerous heat waves. A sweeping 2021 climate report released by the United Nations found the crisis is accelerating, not slowing, increasing the urgency to implement the best possible solutions to curb global climate disaster. So how can cities like Boston hope to succeed in mitigating climate change and cut their own carbon emissions?

Boston University climate and ecology professor Lucy Hutyra is one scientist trying to solve this question. On Oct. 4, she was awarded the prestigious “genius grant” from the John D. and Catherine T. MacArthur Foundation for her research focused on how, when, and where carbon cycles from the plants, soil, water, and air in both forests and urban areas occur. These days, cities emit the majority of fossil fuel emissions, but if they commit to carbon emission reduction, they will need innovative place-based scientific policy research like Hutyra’s to green their urban environments.

Her research builds on years of work examining the carbon cycle in forest and urban environments. Of all her research, Hutyra is particularly proud of a tree-planting app called “Right place, Right tree — Boston,” that she co-created in October 2020 with graduate students from her environmental ecology practicum class. The app guides and informs city planners as well as residents through the decisions they have to make when planting trees. The app helps them choose where to introduce tree canopies, how to consider regional barriers like property ownership or potential community partners, determine which tree species would fare best in the existing environment, and understand the maintenance required to keep them alive. And just as important, the app allows planners to target neighborhoods ravaged by economic and racial inequality, where trees are much less likely to be abundant. Hutyra’s scientific findings in trees in urban environments and the app’s framework are a powerful combination for city planners, scientists, and citizens, even companies to begin designing and implementing their own tree planting programs to mitigate a worsening climate crisis.

Forests and the trees within them are extremely important to the planet, harboring irreplaceable ecosystems and biodiversity, while also removing an average of 2 billion metric tons of carbon annually from earth’s atmosphere since the year 2000. This occurs during photosynthesis when trees draw in carbon dioxide from the air and store it in their wood, plant matter, and soil—yet when Hutyra entered environmental ecology around 2000, urban areas were understudied.

The idea for “Right place, Right tree — Boston” emerged after she took her class to meet with a city official who identified some challenges and needs concerning tree planting in Boston. Conceptually, she explained, she pressed her class to not think in broad “blanket solutions,” like combining a range of solutions together to address the totality of the worsening climate crisis upon the city. Instead, she prompted them to think specifically about what we know about trees in urban environments and how cities can make the most out of trees to mitigate heat and carbon emissions. According to Hutyra, there are a lot of different solutions to climate mitigation, “but what we don’t know is what the optimum implementation strategy looks like.” The app helps address this gap.

The app holds the potential for narrowly focusing on cost-effective and adaptable tree-planting strategies for urban climate mitigation. City planners across the country could implement similar decision-making models using their data and framework they published on GitHub.

There are a lot of choices city planners must navigate when carrying out their duties and many challenging environmental factors when determining the best streets or neighborhoods to plant a specific tree species. Trees need water, of course, but also space to grow without interfering with infrastructure like power lines or pipelines. Trees are often cut down for growing too big and becoming a hazard. All tree species fare differently in varied environments and surroundings. But trees—the right trees—have recently been found to thrive in urban environments.

“In the urban case, it had been assumed that a tree growing in the city was struggling,” says Hutyra. “It’s a terrible place to grow, right? It’s full of pollution, it has no space, all of these kind of notions of a challenging natural environment.” But many of the trees her class studied were found to be thriving. And this was good news, because cities are in dire need of climate mitigating ecological solutions. Across the globe, cities account for over half the world’s population and are industrial epicenters that release about 70% of annual global fossil fuel emissions. “So it’s disproportionately important,” says Hutyra.

Though she is proud of her innovative tree-planting web application that brings together science, city leaders, and citizens, she is adamant that tree planting alone cannot offset a city like Boston’s fossil fuel emissions. More cities have pledged to reduce their carbon emissions, yet many have yet to make significant progress. “While these trees are amazing in what they are able to perform, it’s nowhere near enough,” says Hutyra. “We can’t offset our way out of this in the city.”

The MacArthur “genius” award comes in the form of a grant of $800,000 with no strings attached, which she will receive in installments over the course of four years. At the moment, she has no set plans for the funding but she is excited to continue studying climate change and mitigation in urban environments.

For urban ecology to thrive, she says, “adding an equity lens” to future research is important when seeking solutions to climate mitigation.