Cambridge Can Build Housing and Grow Trees, Too

Our climate-impacted summers aren’t the only source of rising temperatures in Cambridge. The debate between adding housing and preserving the city’s urban forest is becoming ever more heated, as demonstrated in the extensive and impassioned public comment at recent City Council committee hearings.

People are taking sides — between trees and housing expansion, open space and density, climate resilience and affordability. It’s understandable. There are many competing priorities in Cambridge, and not much space.

But a healthy city needs trees and affordable housing alike — and through smart planning and good policy, we can bring about both.

My landscape architecture firm, Reed Hilderbrand, began working with the City of Cambridge on its Urban Forest Master Plan in 2018 and is authoring its 2026 update. I’ve also led research on trends in urban forest planning worldwide. In the process, I’ve learned a few things that might temper this debate and give us some much-needed hope.

Following years of steady decline, the amount of canopy cover — the area of Cambridge shaded by trees — increased from 25 percent to 30 percent between 2018 and 2024, a transformation few thought was possible five years ago. The drastic improvement follows the City Council’s 2021 revisions to the Tree Protection Ordinance and 2023 adoption of “Green Factor” zoning requirements, as well as the substantial tree planting efforts of the city’s urban forestry division.

Of course, the timeframe of this data predates the city’s recent multifamily and inclusionary housing zoning changes, which will certainly have a significant impact on urban canopy.

But we crafted smart policy and took direct action in the face of canopy loss once, and it had a measurable impact. We can do it again — it just requires that we redefine the terms of debate.

Trees are climate infrastructure and canopy cover is an equity issue. The areas of Cambridge with significantly less canopy cover are roughly as much as ten degrees hotter than the shadiest parts of the city. These areas correlate to neighborhoods that were historically redlined, a form of structural and economic racism. They’re also where the city’s most vulnerable populations live today.

We have an opportunity for economic and ecological repair and renewal as we rebuild our city, but not if we continue to grow the discrepancy between leafy neighborhoods of mostly single-family homes and the denser neighborhoods of underserved populations. Trees and affordable housing need to go together.

Forests are dynamic and change is natural. In ecological terms, we describe forests as being in “dynamic equilibrium,” which accommodates perpetual disturbance and regrowth. Whether from a storm, a fire, or the work of a beaver building a dam, trees are constantly falling in the forest, followed by new successional growth. It’s a cycle.

When we develop properties and redesign our city, we disturb the urban forest. That’s unfortunate in the moment, but not catastrophic — if we replant. In the forest, succession happens on its own. In the city, people need to play their part. So, whether compelled by conscience or ordinance, when someone takes a tree down, they need to replant in its place.

The forest doesn’t obey property lines. Trees in one person’s yard cool their neighbor’s houses and the sidewalks we all share. When you dig on your side of the fence, severing roots below grade, you can kill the tree on my side. Trees are the infrastructure of our cities, like the pipes and powerlines that make it function. We need to treat them as such, rethinking regulation to go beyond the boundaries of properties and antiquated spatial models based on dimensional setbacks.

“Green Factor” zoning, a regulatory point system that requires building projects to contribute to environmental cooling through primarily green infrastructure, including large canopy trees, was one tool to do just this. But it was designed before the city eliminated single-family zoning, and needs an update. It should value trees more robustly, reward making space for them to thrive, and protect existing trees (or require their replacement) on adjacent properties and in the public right of way when new development threatens them.

There’s no single answer or single villain in this story. As denser development fueled by recent zoning changes progresses, mature trees will be removed, and the recent trend of canopy growth could easily be reversed.

Looking closely at the data, however, shows that the greatest rate of canopy loss has been within residential properties across Cambridge. It is the dispersed, independent decision-making of everyday residents that most impacts our canopy. So, while developers do have a responsibility to care for our trees and plant new ones, so does everyone else. We can’t just point fingers; we need to work together to nurture our urban forest.

If we reduce the fervor of this understandably heated debate, we can build new flexible regulatory frameworks that care for the forest as a living system, bridge dimensions of property and ownership, and, most importantly, build a culture of shared responsibility.

With the political will to update the policies protecting our urban canopy, we can optimize our limited space to achieve more housing and a shaded city, making Cambridge a healthier and more equitable place to live.

Eric F. Kramer is a graduate of the Harvard Graduate School of Design and a Fellow of the American Society of Landscape Architects.