Like most, I picked up and rediscovered several hobbies during the pandemic. I was inspired by Beth Harmon and dusted off the chess board. I snagged a community garden plot and spent more growing a single strawberry than those that are store bought. I learned how to identify at least 10 birds in my neighborhood through their songs alone.
But hobby no. 231 — identifying trees in my neighborhood — stuck and became a favorite. A party trick I never quite got to use was the new ability to quickly spot the differences between a Sugar maple, a red maple and a trident maple simply by looking at their bark.
As the hobby grew on dog walks, so did my awareness of tree species and where different species naturally occur. At various points in my life, I’ve lived along the West, East and Gulf coasts and I began to slowly notice overlap of trees despite the distinct climates.
And though it was subtle, I noticed that younger native trees began to struggle more often than non-native trees, but trees I associated the South were planted more and performed better In D.C. So I wanted to understand how urban forests were changing. Were cities increasingly relying on trees from warmer regions? And if so, what would that mean for the future look of American neighborhoods?
I collected research and federal data that shows trees across various climate zones across the U.S. have adapted to zones that lie outside their typical ranges. This is most true for communities where climates are cooler, in which trees found in warmer climates have begun to encroach. Some cities have even begun purposely planting trees from regions outside their own to diversify their canopies.
And they’re often have ranges that span from the Midwest to the south which are known to have hardy trees that can withstand harsh climates and long periods of drought.
I took a dataset from 65 U.S. cities, courtesy of the work by a team of researchers at Stanford, Harvard, Cornell and Worcester Polytechnic Institute, and then merged it with data from the USDA. The dataset from 2023 contains more than five million trees — and includes variables like date planted, height and common name of the tree. The USDA dataset contains richer data like the expected lifespan of a tree, its tolerance to fire and flower colors.
Merging the two took quite a bit of work and it’s not perfect, but might be a close proxy for which trees are found in each city. The main issue you’ll notice if you play around with this data is that many trees have multiple common names. The sugar maple can also be known as the rock maple, the sugar tree, the hard maple or even the sweet maple.
We won’t mention several misspellings of tree names, but question time — which is the correct spelling for this tree:
Arbrovitae
Arborvate
Arborvie
Trick question. None of the above.
It’s Arborvitae.
Warming temperatures have accelerated tree migration and alter how cities think about tree planting. But that means the canopy in your city will have a different look and feel to it. But through through a combination of exact and fuzzy matching on the common names and scientific names, I managed to combine nearly all five million trees, creating a database of the characteristics of trees in each city.
The USDA also provides a list of counties in which the tree is most commonly found. In other words, I was able to tie trees in the database to the distribution data to track its typical range.
Trees in Louisiana are resistant to drought and heat and hate the cold, but they’re in places like New York and Pennsylvania. The same is true for trees in Houston, which have found their way to the Bay Area. The trend I began to notice as an amateur tree watcher (tree gazer, woodland watcher, arborist?) started to make sense.
The explanation is quite simple.
“For some plants and trees, moving north is real and their only chance for survival,” wrote Chris Woodall, a USDA research forester for Northern Research Station in a study about the migration of trees. “Our study confirms a link between global warming and forest migration. It’s no longer conjecture.
And for other trees, as states begin to warm up, their ranges expand.
It’s beyond the scope of this post, but there’s more to the science of how or why trees spread and there’s also literature on the efforts cities are taking to make their canopies more climate resilient. And with climate change, cities need more from trees, which are often used as decoration. Now they are being asked regularly to provide shade, withstand drought and fire and restore ecosystems.
So if you live in a cooler climate, the next time you're in places like Atlanta, St. Louis or Houston, take note of the trees lining neighborhoods and shading parks — many of those species are already moving north, and some may already be growing on your block.
Find the data and code on Github!
Tree-mendous reads I’ve enjoyed while researching this piece:
A Race to Save a Signature American Tree From a Deadly Disease: https://www.nytimes.com/2025/08/13/realestate/beech-leaf-disease.html
Like AC for the Outdoors: https://www.theatlantic.com/ideas/archive/2025/07/shade-climate-change/683578/
