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Built-Out Barcelona Makes Space for an Urban Forest

A rendering of Barcelona’s planner green corridor network, showing the enlarged park at Plaça de les Glories Catalans at its heart. Ajuntament de Barcelona

The city is planning a major green makeover to combat the heat island and create a more welcoming place for humans and animals alike.

When a city needs green space, but it’s all out of room, what can it do?

It’s an issue that many older, denser cities are facing as they try to make themselves more amenable to their citizens and the environment. For Barcelona, this challenge requires especial ingenuity. Take a walk around what is one of Europe’s most densely populated city cores and you’d be forgiven for pronouncing the place full.

With an intense knot of historic masonry at its heart, Spain’s second city doesn’t display the most obvious potential as a future green paradise. But it badly needs new green spaces to battle its heat island effect, manage air and noise pollution, and generally improve citizens’ quality of life.

That’s why, on Monday, the city nonetheless rolled out a paradigm-shifting re-greening program, one that will double the number of trees in the city, increase park space by two thirds, and give each citizen an extra square meter of green areas. The urban plan, which will deliver 108 acres of new green space by 2019 and over 400 acres by 2030 is a model of ingenuity that could serve as a model for other cities.

Barcelona’s problem is not that it currently lacks parks. Its Parc de Collserola, which extends out from its western suburbs, covers a vast 80 square kilometres. The problem is that its green space is very unevenly distributed. Almost all of Barcelona’s larger parks are on the slopes rising up to the modest mountain range that backs the city. This works well as a weekend getaway and general backdrop, but they’re far from the city’s centers of activity.

In its core, Barcelona is built up more or less to the last square inch, with a network of historic streets and alleys supporting a population density greater than Manhattan’s. This area’s sea of buildings is sometimes softened with avenues of trees, small gardens, and one modest but beautiful park—but it can still feel heavy-aired and claustrophobic on Barcelona’s many hot days.

View from the Parc dels Tres Turons, located in the hills behind Barcelona’s city center. (Ajuntament de Barcelona)

This imbalance may partly contribute to major differences in temperature between the city’s center and its periphery. Temperatures are typically up to 7 degrees Celsius (11 degrees Fahrenheit) higher in the old town than in the city’s greener, higher suburbs. Cities on the Iberian peninsula have always adapted carefully to intense summer heat. Streets stay narrow to provide shade, while south-facing windows often stay covered with awnings and shutters in the hotter months to keep interiors cool without automatic resort to air conditioning. Still, in a city where summer highs already regularly reach above 90 degrees Fahrenheit, climate change will see Barcelona only get warmer, drier and potentially more uncomfortable. Plans to green the city are thus not merely about creating a more pleasant-looking urban environment—they’re an essential step toward ensuring that inner Barcelona stays liveable in summer.

No major park can be carved out of an environment this densely built, but the city nonetheless plans to transform its core into a blooming mosaic of plants and leaf cover. The city has found space for five new gardens, which will ultimately be linked up to existing open spaces with lush new corridors of greenery that will create a seamless habitat for urban fauna. Green roofs will soften the sun’s glare, creepers will extend across bare walls, and temporary gardens will squat on sites waiting for construction, cooling and freshening their surroundings.

Barcelona’s green corridor network as it will appear when complete. The dark green land in the top left is the Parc de Collserola, which stretches from the city far out into the surrounding region. (Ajuntament de Barcelona)   

The five new gardens, many of which are already under construction, are a lesson in finding space where there doesn’t appear to be any. The largest one will spring up around a major city square; the land used to belong to road traffic, but those cars are now being diverted into nearby tunnels. A small park was already created at Plaça de les Glòries Catalanes, and by burying elevated roads that currently criss-cross the space, the city has found a way to greatly extend it and make the resulting oasis much calmer.

Another green space will be made—controversially—by clearing away a large courtyard block in the city center that is currently partially filled by squatted, single-story 1920s workshops. A third public space will be created by opening the lush, mature 7.5-acre garden of a newly created house museum to the public. A fourth parkwill be opened on what is currently a small, scrappy piece of ex-industrial semi wasteland in the hinterlands behind the city’s main container port, and a fifth will be created as part of a long-stalled but newly revived redevelopment of an outlying barracks.

An already constructed interior courtyard garden in the Example District. (Ajuntament de Barcelona)

Arguably the biggest change isn’t from the parks, but from the policies designed to connect green spaces into one leafy network. Ten large interior courtyards in Barcelona’s Eixample district will be planted with trees, while 10 city squares will get parking restrictions that allow for more plantable area. New or enlarged avenues of trees will thread this network together along major streets with surfaces that are more permeable to rain, so that birds and insects can spread across a seamless habitat.

If Barcelona seems especially keen on these corridors, it’s partly because they have already been tried and proved a success. In 2000, the city opened a long, slender park along the banks of the river Besós, a formerly filthy stream passing through industrial lands in the city’s northeast. Since being cleaned up and partly reopened to the public (some areas are protected wetlands), the river banks (viewable here) have thrived with plants suited to brackish water while the river itself is now alive once more with eels, frogs, and terrapins.

How the green corridors could look at ground level.Ajuntament de Barcelona

Back in town, the city is also stumping up a lot of cash to promote green roofs. The city has just called for applications for 50 bursaries of €1,500 to create greening plans for roofs across the city. The top 10 of these submissions will be eligible for grants of up to €100,000 per roof, while elsewhere the city will get new bird and bat boxes, rooftop hives, and insect hotels. Creeper will also be planted and trained across bare walls.

Taken individually, all these microprojects are tiny drops in the bucket. Together they will work to form a flood, creating a future Barcelona that is greener, fresher, more sustainable, and more humane.

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Cities Should Think About Trees As Public Health Infrastructure


Cities Should Think About Trees As Public Health Infrastructure

Planting trees is an incredibly cheap and simple way to improve the well-being of people in a city. A novel idea: Public health institutions should be financing urban greenery to support well-being and air quality.

Cities Should Think About Trees As Public Health Infrastructure
“It’s not enough to just talk about why trees are important for health.” [Photo: Claudel Rheault/Unsplash]

Think of a tree-lined street in the midst of a busy city. It feels like something of a treasure: hushed, cool, and sheltered from noise and sidewalk glare.

These leafy streets cannot afford to be seen as a luxury, argues a new report from The Nature Conservancy. Trees are sustainability power tools: They clean and cool the air, regulate temperatures, counteract the urban “heat island” effect, and support water quality and manage flow. Yes, they look pretty, but they also deliver measurable mental and physical health benefitsto concrete-fatigued city dwellers.

So with evidence to back up all the benefits of urban greenery, TNC set out to answer, in this report, the question of how cities can develop innovative financial structures and policies to plant more trees.

Urban trees remove enough particulate matter from the air to create up to $60 million worth of reductions in healthcare needs. [Photo: Flickr user Helen Alfvegren]

It’s a particularly pressing question now, because despite overwhelming evidence testifying to the environmental and health benefits of urban trees, their presence is declining in cities across the U.S. Around 4 million urban trees die or disappear each year, and replanting efforts have failed to keep pace, even though a 2016 study on California from the U.S. Forest Service found that every $1 spent on planting trees delivers about $5.82 in public benefits.


Because urban trees are often slotted into the “luxury” or “nice to have” category in city budgeting decisions–certainly less prioritized than public safety and infrastructure maintenance–funding is often inadequate, and fails to treat trees as a long-term investment, and certainly not one that can deliver health benefits. The standard rate of investment in trees is around one-third of a percent of a city’s budget, says Rob McDonald, TNC cities scientist and lead author on the report. “It’s not enough to just talk about why trees are important for health,” McDonald says. “We have to start talking about the systemic reasons why it’s so difficult for these sectors to interact–how the urban forestry sector can start talking to the health sector, and how we can create financial linkages between the two.”

TNC estimates that coming up with the capital necessary to maintain our current urban canopy, and expand it to the point where it creates consistent health benefits, would require an annual investment, on average, of $8 per person–a sum that would just about double current municipal tree-planting budgets. That figure is hypothetical and meant to suggest not that funding for trees should actually come from U.S. residents, but that the project is well within the scope of affordability.

What if, McDonald asks, that funding could come from the health sector? A 2013 study found that urban trees remove enough particulate matter from the air to create up to $60 million worth of reductions in healthcare needs at the city level. If public health spending in cities increased by just 0.1% or $10 per person, that would create enough public investment to finance the maintenance and expansion of urban forests and deliver the resulting health benefits. Again, this is just a rough model, but the case for treating trees as infrastructure that supports public health, and eventually could reduce the need for spending in that sector, is strong.

“We have to start talking about the systemic reasons why it’s so difficult for these sectors to interact–how the urban forestry sector can start talking to the health sector, and how we can create financial linkages between the two.” [Photo: Flickr user Veni]

There’s a wrinkle in this idea, McDonald says, and it derives from the fact that while cities are the agencies that pay for trees, they do not necessarily oversee health spending. That often falls to the state, or large local insurers. “But one big goal of this report is to get a variety of health agencies to see that they should be participating in the urban greening conversation,” McDonald says. In fact, the Affordable Care Act has created a $16 billion prevention fund to be funneled into communities working on widespread health-supportive initiatives; urban trees, McDonald says, could fall under that purview. And Kaiser Permanente, a large insurer in Northern California, announced last year a $2 million investment in public parks in low-income communities in the Bay Area.Diversifying funding sources for urban greenery–and casting trees as a health investment–could also begin to close the socioeconomic gap in access to parks and green space, too. A 2013 UC Berkeley study found that compared to white people, black people were 52% more likely to live in sparsely shaded, and consequently, much hotter, parts of the city, and have less access to green spaces. While initiatives like New York City’s Million Trees NYC have made a concerted effort to create more equity when it comes to green space in the city, often, trees are added to neighborhoods only at the behest of community groups. Those with more financial resources, McDonald says, are often more likely to make and be granted those requests.

Creating greener cities cannot be the responsibility of the health sector alone; McDonald says it will be crucial for urban forestry departments to more fully integrate the health benefits of their trees into messaging and goals in order to break down city agency silos and communicate more effectively with urban health and planning departments. And of course, as more and more cities develop strategies to create resilience against climate change, a healthy urban canopy will be a hugely necessary component.


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The Fruit Bowl still fresh as ever at 70

STOCKTON — A lone eucalyptus tree, more than 100 years old, still stands on the edge of Waterloo Road where Frank and Ina Lucchetti sowed the seeds of their family business.

It remains large and firm, the only survivor of the 1946 chimney fire that burned down the family’s home and adjacent trees and of the 1991 frost that claimed its two remaining companions. The tree’s thriving existence resembles that of the simple fruit stand it helped provide shade for many years ago.

In early 1947, Frank and Ina Lucchetti rented a home in the eastern fringes of Stockton that was surrounded by nine acres of walnuts, peaches and plums. By summer, the first bounty of ripe nectar white freestone peaches at the property was ready to be picked. But the market wasn’t profitable.

Taking a friend’s suggestion, the young couple placed a table and signs on the side of the road to sell their fruit during the busy Fourth of July weekend. On the counter, Ina Lucchetti kept a bowl of just-picked peaches, plums or apricots for customers to sample.

And so it became known as The Fruit Bowl.

The once-small fruit stand now is a market and bakery at 8767 Waterloo Road in Stockton with an ample selection of products, including pasta, peaches, pies and paninis. It opened for its 70th season in April.

Ralph Lucchetti, one of three sons born to Ina and Frank Lucchetti, now runs The Fruit Bowl with help of his wife, Denene.

On a recent afternoon, as vehicles whizzed by the busy road, some slowed to turn into the market’s parking lot — just as others had done over the past seven decades.

Lucchetti wasn’t encouraged by his parents to pursue the family business. His father, in fact, thought he was nuts to want to get into farming. But, after five years of working elsewhere, he decided to return to his roots at his family’s ranch and market.


“It’s home,” Lucchetti said. “I wanted to continue on if I could, and it worked out pretty well.”

Denene Lucchetti said keeping The Fruit Bowl open is important to her husband because his parents started it, and of the three brothers, he’s the only one who went into farming.

Alongside their son and daughter-in-law, Ina and Frank Lucchetti helped keep The Fruit Bowl going for as long as they could and were able to see the completion of the market and the addition of the bakery.

Frank Lucchetti died in 2004 and Ina Lucchetti in 2011.

“They put a lot of hard work in, and my wife and I as well,” Ralph Lucchetti said.

Part of The Fruit Bowl’s success comes from Ralph Lucchetti staying as true as possible to the business’ origins of selling what’s grown at the ranch — he and an employee pick only enough fruits each morning to sell for the day to ensure freshness — and the practice has resulted in a loyal following over the years. The Fruit Bowl also stocks local produce and other items to provide people a one-stop shopping experience.

One woman, who was on her way out of the market after buying a box of cherries, asparagus, strawberries and more, said “this is the best” about The Fruit Bowl. She had been shopping there for more than 40 years, she quickly added as she hauled away her purchase.


“Regulars” will stop by the market two to three times a week. Some people making The Fruit Bowl their usual rest stop between their trips to the Bay Area and the mountains, and vice versa.

The result has been not only a dedicated clientele, but lifelong friends for the Lucchettis, which is part of the appeal of continuing the business, Ralph and Denene Lucchetti said.

The customers are great, and the Lucchettis have gotten to know some of them very well over the years, Denene Lucchetti said.

Ralph Lucchetti recalled one of those customers-turned-family friends was New York Yankee Frank Crosetti.

Sitting at a picnic table just steps from the house where he grew up, Ralph Lucchetti recalled Crosetti would stop by to sit under the shade of a tree and chat with his father. Crosetti once brought over his World Series ring to show a young Ralph.

And it’s not just the customers who are memorable — employees also have been at the root of The Fruit Bowl’s history.

Marie Barbagelata was 13 when she was hired by Ina and Frank Lucchetti to work at their ranch and stand.


The now 76-year-old said she learned such great skills — dealing with customers, counting back change — and work ethic from working at The Fruit Bowl, that she encouraged her daughters and granddaughters to work there. They did.

“It was an all-around good experience,” she said. “I feel like they’re family for me … Ina was one of my idols.”

Ralph Lucchetti said he’s not sure what’s in the future of The Fruit Bowl or whether one of his kids — he and Denene Lucchetti have three children — will continue in the family business or if it will make financial sense to stay open, he said.

Denene and Ralph Lucchetti aren’t ready to let it go, though.

Said Ralph Lucchetti: “We haven’t given up yet.”

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Atlanta’s Visionary Beltline


The multi-use trail system is driving economic, environmental and cultural renewal — while saving the city millions of dollars.
Intro imagePhoto courtesy of Trees Atlanta

Brilliant shades of purple, yellow and orange beckon hikers and bikers to maturing meadows in the urban center. Parents stroll children along trails cooled by the fragrant breezes of native magnolia, dogwood, oak and long leaf pine trees. Families picnic near a 40-foot cascading waterfall.

This scene in the heart of Atlanta, Georgia, is a far cry from what it was nine years ago. Back then, trucks illegally dumped toxic chemicals, trash and tires here. Kudzu and other weeds flourished, forming ad hoc habitat for rats and copperhead snakes.

Now, the Atlanta BeltLine is wiping out blight with 33 miles of multi-use trails along a historic rail line that encircles the city’s core. The ring of infrastructure is boosting environmental awareness in a metropolis that has been better known for suburban sprawl than parklands. Although other cities are turning abandoned tracks into greenways, the US$4.8 billion project connecting 45 neighborhoods offers unique lessons on urban renewal.

Master Vision

It was a master’s degree thesis that sparked the movement to build the BeltLine. In 1999, Ryan Gravel, then an architecture student at Georgia Tech, envisioned and fleshed out a plan to build a modern transit system to replace a ring of decaying rail tracks that encircled the capital city.

Atlanta’s BeltLine is replacing urban blight with multi-use trails and greenery along 33 miles of former rail line. Map courtesy of Atlanta BeltLine, Inc.

It took several years of negotiating among politicians, city officials, community advocates, real estate developers, landscape architects and environmentalists to solidify a proposal. Then, in 2006, Atlanta established the Atlanta BeltLine, Inc., known as ABI, to lead a renovation funded by private donors and the city that includes bike trails, parks, water management systems, housing, electric transit, art sculptures and more. According to Gravel, the project is the most extensive of its kind in the United States.

“I wanted to make Atlanta a place I wanted to live in,” he says. “Who would have thought that this idea would take off? It has been fun, excruciating and rewarding.”

Bringing Back Biodiversity 

This network-in-the-making is boosting environmental awareness in a city that used to be better known for its traffic jams and sewage-polluted streams. Efforts to clean up 1,100 acres (450 hectares) of contaminated brownfields and plant more than 3,000 indigenous trees and grasses are bringing back biodiversity not seen in decades.

“The native plantings they have done had a tremendous positive impact,” says Berry Brosi, associate professor of environmental science at Emory University. “We found enormous areas in terms of pollinator abundance.”

Pollinator-friendly vegetation is helping boost biodiversity and rebuild healthy ecosystems along the trail. Photo courtesy of Trees Atlanta

In fact, an unpublished study Brosi conducted found on average three times as many bee species and five times as many bees in pollinator planting sites along the BeltLine than in mowed grass.

“I noticed for the first time in my backyard, we are seeing bees, butterflies, even fireflies, which is different than four years ago,” says Chad Ralston, who lives nearby and bikes almost daily.

One major reason for the increase in biodiversity has been the native forest created under the supervision of Trees Atlanta, a non-profit organization dedicated to protecting Atlanta’s urban canopy. Trees Atlanta has planted 19 acres (8 hectares) of indigenous trees and grasses around the abandoned tracks. Ten more acres of reforestation are planned for next year.

“It has been a challenge in what different parts of the community want and what we want,” says Greg Levine, the organization’s co-executive director and chief program officer. Local residents like the green space, Levine says, but often prefer it manicured.

“They want more mowing, and then you don’t have the pollinator habitat,” Levine says. “They like the look of a meadow, but it takes three years.” Levine says Trees Atlanta and the city have reached an agreement to just mow along the edges of the path once a year, keeping the trails clear. Goats are also used to munch on the nonnative kudzu for environmental and economic benefits.

Economic Boon

As Head of Growth and Grassroots for ASW Distillery, Ralston helped convince his company to open a new location on a part of the BeltLine known as the Westside Trail. The real estate in the vicinity is booming and is the biggest economic driving force in the city, says Atlanta mayor Kasim Reed.

Real estate is booming along the BeltLine. Photo courtesy of Trees Atlanta

Meanwhile, Atlanta is discovering that going green can save money. The city was planning to build a US$40 million concrete vault and tunnel system to store stormwater in the Fourth Ward. Every time it rained flooded sewers sent pollution into local streams, and the city had already paid the federal government more than US$19 million in fines for its cracked and broken sewer system.

ABI stepped in to work with city officials to develop a better way to deal with storm water and sewage. The plan was to build a park bordering the Eastside Trail that recycles stormwater for a lake, fountain and waterfall. The ABI team saved the city at least US$15 million in stormwater infrastructure costs with its innovative design for the Historic Fourth Ward Park.

Cost savings “are where we hook people in,” says Heather Hussey-Coker of ABI. “But we solved one of the issues in a green way, a beautiful way.”

“The park has won awards for its plantings [and] wetlands, now home to Canada geese, ducks and turtles,” says Kit Sutherland, a community advocate who helped build the 17-acre (7-hectare) park. It also set the standard for how the BeltLine and Atlanta work together to transform former industrial areas whose belching chimneys earned them the title of “sewers of smoke.”

The Atlanta BeltLine is trying to create more energy than it uses, too. An architectural solar canopy provides shade and sells electricity back to Georgia Power. Solar-powered trash compacter bins help save the city time, energy and money by wirelessly transmitting signals to garbage collectors when it’s time to empty the cans, instead of having trash picked up on a schedule even if the cans are not full. LED lampposts line pathways, saving electricity and minimizing light pollution.

The city’s West Side is about to get a big boost because of the BeltLine. An abandoned quarry will soon add 300 acres (121 hectares) of green space adjacent to the Westside Trail. The new Westside Reservoir Park will be a source for 30 days of water, instead of Atlanta’s current three-day supply. Even though last year’s drought has ended, Atlantans still face watering restrictions because the city’s major reservoir is below full pool. Lawns can only be watered two days a week, and home car washes are forbidden.

Changing Lifestyles

Reed says the corridor is altering the way people get around. “It’s a healthy form of mobility. The bike paths and trails are changing the way in Atlanta we live,” he says. “The greater the density, the less pollution.”

BeltLine designers turned a former bus repair facility along the route into a 6-acre urban farm. Photo courtesy of Atlanta BeltLine, Inc.

It’s changing diets, too. BeltLine designers transformed an old bus repair facility with underground fuel tanks into a 6-acre (2.4-hectare) urban farm. They cleaned up arsenic-stained soil and excavated buried garbage to revitalize the ground. Now urban farmers produce an abundance of cucumbers, tomatoes, carrots and other vegetables that feed a neighborhood unaccustomed to fresh produce. The rest is sold at the nearby Ponce City Market, once an abandoned department store that has been revitalized into a thriving shopping and food court that serves as the commercial anchor of the BeltLine.

But success is triggering new problems. With the real estate boom catalyzed by the BeltLine’s infrastructure, affordable housing is scarce, and the trail is crowded. There is little research on the environmental impacts the increased density and expanded use have spawned. Construction of 22 miles of light rail transit next to the paths is expected to alleviate some of these concerns.

“The light rail will help with changing lifestyles,” says Ralston. “I’m one of those millennials. I don’t care to drive. I don’t like sitting in traffic.”

“I get it,” Gravel says. “There is anger about the BeltLine being overcrowded. I bike. But that just means we need more bike lanes.”

Mildred Spalding, a biker who has lived in Atlanta for 43 years, was one of the 1.7 million Eastside trail users last year.

“It’s the best thing ever to happen to Atlanta,” she says. “It’s changing how I think of Atlanta.”

For Gravel, the BeltLine’s visionary, it’s a dream come true, not only professionally but personally as well.

“Not long ago, I had to take my kids with me to the grocery store,” he says. “My kids didn’t want to ride in the car. ‘Can’t we ride our bikes instead?’ Of course we can, that’s what people in Atlanta do. We ride bikes to the grocery store.” View Ensia homepage

Editor’s note: Judith Moen produced this feature as a participant in the Ensia Mentor Program. Her mentor for the project was Nate Berg.

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American Trees Are Moving West, and No One Knows Why

American Trees Are Moving West, and No One Knows Why

Climate change only explains at least 20 percent of the movement.

Autumn colors in Great Smoky Mountains National Park, near Cherokee, North CarolinaGeorge Rose / Getty
A new survey of how tree populations have shifted over the past three decades finds that this effect is already in action. But there’s a twist: Even more than moving poleward, trees are moving west.

About three-quarters of tree species common to eastern American forests—including white oaks, sugar maples, and American hollies—have shifted their population center west since 1980. More than half of the species studied also moved northward during the same period.

These results, among the first to use empirical data to look at how climate change is shaping eastern forests, were published in Science Advances on Wednesday.

Trees, of course, don’t move themselves. But their populations can shift over time, and saplings can expand into a new region while older growth dies in another. The research team compared a tree population to a line of people stretching from Atlanta to Indianapolis: Even if everyone in the line stood still, if you added new people to the end of the line in Indiana and asked others in Georgia to leave, then the center of the line would move nonetheless.

The results are fascinating in part because they don’t immediately make sense. But the team has a hypothesis: While climate change has elevated temperatures across the eastern United States, it has significantly altered rainfall totals. The northeast has gotten a little more rain since 1980 than it did during the proceeding century, while the southeast has gotten much less rain. The Great Plains, especially in Oklahoma and Kansas, get much more than historically normal.

“Different species are responding to climate change differently. Most of the broad-leaf species—deciduous trees—are following moisture moving westward. The evergreen trees—the needle species—are primarily moving northward,” said Songlin Fei, a professor of forestry at Purdue University and one of the authors of the study.

There are a patchwork of other forces which could cause tree populations to shift west, though. Changes in land use, wildfire frequency, and the arrival of pests and blights could be shifting the population. So might the success of conservation efforts. But Fei and his colleagues argue that at least 20 percent of the change in population area is driven by changes in precipitation, which are heavily influenced by human-caused climate change.

Where the center of population of tree species shifted between 1980 and 2015 (Fei et al. / Nature Advances)  

“This is a very cool study, with results that seem to raise more questions than they can provide answers for,” said Loïc D’Orangeville, an ecologist at the Quebec Forest Research Center who was not connected to the study, in an email. “West is usually drier in the study region, so although it’s been wetter in the recent decades, it’s still drier than the East.”

“I can’t really make up [for] that moisture attractiveness for trees,” he added.

The movement of conifers and other needle trees north makes much more sense. Conifers are already more vulnerable to temperature than flowering, deciduous trees. They also already populate the boreal forest of eastern North America, so they’re well-adapted to the colder, drier conditions they will find as they expand north in the United States.

Fei and his colleagues don’t know if the westward trend will continue. We may have already seen the peak of westward movement, and northward expansion may soon outrank it. “When the result came out that trees are moving westward, our eyeballs opened wide. Like, ‘Wow, what’s going on with this?’ The results seem to show that moisture plays a much more significant role in the near-term, which is very intriguing,” he told me.

The survey draws on the U.S. Forest Service’s Forest Inventory and Analysis Program, a kind of continuously running census of the country’s tree population. The program, which stepped up in 1978 but which has been conducted in some form since the 1930s, surveys the health, density, and species mix of forested areas across the country. It examines not only the majestic, landmark tracts of untrammeled forest (like George Washington National Forest) but the humbler woods, as well: stands of trees near the highway, at the edge of housing developments, and in the middle of city parks.

“This is not a modeling exercise, there are no predictions, this is empirical data,” said Fei. “This study is looking at everything everywhere in the eastern United States.”

What concerns the team is that—if deciduous trees are moving westward while conifers move northward—important ecological communities of forests could start to break up in the east. Forests are defined as much by the mix of species, and the interaction between them, as by the simple presence of a lot of trees. If different species migrate in different directions, then communities could start to collapse.

“If you have a group of friends, and people move away to different places—some go to college in different places, and some move to Florida—the group is … probably going to fall apart,” Fei said. “We’re interested in whether this tree community is falling apart.”

“These results show contemporary proof of something we know has happened before and will happen again: that trees are highly dynamic organisms, constantly moving in response to climatic shifts like recent glaciations or other disturbances. Their actual range does not reflect conditions that are optimal for their growth,” said D’Orangeville.

Any tree’s range represents “a legacy of historical migrations and battles lost against other species or disturbances. With climate change however, their capacity to keep pace with the fast-changing climate is a major issue.”