Here are 5 practical ways trees can help us survive climate change

by Gregory Moore, The Conversation

Credit: Shutterstock

As the brutal reality of climate change dawned this summer, you may have asked yourself a hard question: am I well-prepared to live in a warmer world?

There are many ways we can ready ourselves for climate change. I'm an urban forestry scientist, and since the 1980s I've been preparing students to work with trees as the planet warms.

In Australia, trees and urban ecosystems must be at the heart of our climate change response.

Governments have a big role to play—but here are five actions everyday Australians can take as well.

1. Plant trees to cool your home

At the current rate of warming, the number of days above 40℃ in cities including Melbourne and Brisbane, will double by 2050—even if we manage to limit future temperature rises to 2℃.

Trees can help cool your home. Two medium-sized trees (8-10m tall) to the north or northwest of a house can lower the temperature inside by several degrees, saving you hundreds of dollars in power costs each year.

Green roofs and walls can reduce urban temperatures, but are costly to install and maintain. Climbing plants, such as vines on a pergola, can provide great shade, too.

Trees also suck up carbon dioxide and extend the life of the paint on your external walls.

Trees can cool your home by several degrees. Credit: Shutterstock

2. Keep your street trees alive

Climate change poses a real threat to many street trees. But it's in everyone's interests to keep trees on your nature strip alive.

Adequate tree canopy cover is the least costly, most sustainable way of cooling our cities. Trees cool the surrounding air when their leaves transpire and the water evaporates. Shade from trees can also triple the lifespan of bitumen, which can save governments millions each year in road resurfacing.

Tree roots also soak up water after storms, which will become more extreme in a warming climate. In fact, estimates suggest trees can hold up to 40% of the rainwater that hits them.

But tree canopy cover is declining in Australia. In Melbourne, for instance, it falls by 1-1.5% annually, mainly due to tree removals on private land.

This shows state laws fail to recognize the value of trees, and we're losing them when we need them most.

Infrastructure works such as level crossing removals have removed trees in places such as the Gandolfo Gardens in Melbourne's inner north, despite community and political opposition. Some of these trees were more than a century old.

So what can you do to help? Ask your local council if they keep a register of important trees of your suburb, and whether those trees are protected by local planning schemes. Depending on the council, you can even nominate a tree for protection and significant status.

But once a development has been approved, it's usually too late to save even special trees.

Governments are removing trees from public and private land at the time we need them most. Credit: Shutterstock

3. Green our rural areas

Outside cities, we must preserve remnant vegetation and revegetate less productive agricultural land. This will provide shade and moderate increasingly strong winds, caused by climate change.

Planting along creeks can lower water temperatures, which keeps sensitive native fish healthy and reduces riverbank erosion.

Strategically planting windbreaks and preserving roadside vegetation are good ways to improve rural canopy cover. This can also increase farm production, reduce stock losses and prevent erosion.

To help, work with groups like Landcare and Greening Australia to vegetate roadsides and river banks.

4. Make plants part of your bushfire plan

Climate change is bringing earlier fire seasons and more intense, frequent fires. Fires will occur where they hadn't in the past, such as suburban areas. We saw this in the Melbourne suburbs of Bundoora, Mill Park, Plenty and Greensborough in December last year.

It's important to have a fire-smart garden. It might seem counter-intuitive to plant trees around the house to fortify your fire defenses, but some plants actually help reduce the spread of fire—through their less flammable leaves and summer green foliage—and screen your house from embers.

Depending on where you live, suitable trees to plant include crepe myrtle, the hybrid flame tree, Persian ironwood, some fruit trees and even some native eucalypts.

Gardens play a role in mitigating fire risk to your home. Credit: Shutterstock

If you're in a bushfire-prone area, landscape your garden by strategically planting trees, making sure their canopies don't overhang the house. Also ensure shrubs do not grow under trees, as they might feed fire up into the canopy.

And in bad fire conditions, rake your garden to put distance between fuel and your home.

5. What if my trees fall during storms?

The fear of a whole tree falling over during storms, or shedding large limbs, is understandable. Human injury or death from trees is extremely rare, but tragedies do occur.

Make sure your trees are healthy, and their root systems are not disturbed when utility services such as plumbing, gas supplies and communication cables are installed.

Coping with a warming world

Urban trees are not just ornaments, but vital infrastructure. They make cities livable and sustainable and they allow citizens to live healthier and longer lives.

For centuries these silent witnesses to urban development have been helping our environment. Urban ecosystems depend on a healthy urban forest for their survival, and so do we.

Local water availability is permanently reduced after planting forests

Smithsonian study reveals carbon markets undervalue shade-grown coffee farms

Existing shade trees on coffee farms store more carbon than tree-planting projects can sequester

Smithsonian

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The diversity of trees on shade-grown coffee farms makes them a haven for biodiversity.  

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Credit: Roshan Patel, Smithsonian’s National Zoo and Conservation Biology Institute.

A new global analysis reveals a critical oversight in sustainable coffee and carbon-capture initiatives. These programs incentivize the planting of new trees yet fail to reward the preservation of mature shade trees in existing agroforestry farms, despite their far greater carbon storage potential.   

According to new research from the Smithsonian’s National Zoo and Conservation Biology Institute (NZCBI) and Smithsonian Tropical Research Institute (STRI), published today in the journal Communications Earth & Environment, more than twice as much carbon stands to be lost through the removal of non-coffee shade trees than might be gained through tree planting—even if every plantation-style coffee farm in the world planted new shade trees.    

Globally, coffee farms cover more than 10 million hectares. Farming systems vary in intensity, from plantation-style monocultures to agroforestry systems with native trees that provide shade, wildlife habitat and carbon storage. Planting new shade trees is currently incentivized through carbon markets, which allow coffee farmers to sell carbon credits generated via tree planting. However, existing agroforestry systems are rapidly converting to monoculture plantations, releasing significant amounts of carbon into the atmosphere while destroying habitat.  

Scientists from NZCBI and STRI identified a critical gap in current carbon markets, which compensate coffee farmers for planting new trees but not for protecting standing trees. This potentially creates an incentive to remove existing trees to plant new ones that store less carbon but would be eligible for carbon-credit payments.    

“There is a lot of money behind planting trees on degraded coffee farms, yet there are basically no financial incentives, outside of the Smithsonian Bird Friendly certification, to protect standing shade trees,” said NZCBI ecologist Ruth Bennett, senior author of the study and leader of Smithsonian Bird Friendly program, which offers a gold standard certification for coffee and cocoa farms that conserve high-quality habitat for wildlife. “To be clear, planting shade trees on monoculture coffee farms is a positive step, but our findings show tree planting alone can’t make up for what you lose when you remove mature shade trees.”  

The study, conducted in collaboration with The Nature Conservancy and CIRAD, also found carbon-focused tree planting efforts do not necessarily boost biodiversity. Carbon sequestration is optimized by maximizing tree density, while biodiversity benefits more from tree diversity.  

“To protect nature and fight climate change, coffee companies need to focus on planting a diversity of the right trees, not just planting a high density of fast-growing trees that capture carbon,” said Emily Pappo, the study’s first author and a postdoctoral climate fellow at the Smithsonian.    

Prior research demonstrated coffee farms that include a diverse mixture of shade trees harbor roughly four times more bird species than coffee monocultures. Such findings are at the heart of the Bird Friendly coffee certification criteria, which ensure farms maintain dense and diverse shade trees. This certification grants farmers access to specialty markets and enables them to set higher asking prices, rewarding them for conserving biodiversity.    

Coffee farmers are facing economic pressure and reduced yields due to climate change, and some are responding by removing shade trees on their properties in hopes of producing more coffee, even though scientists believe shade trees may help producers adapt to climate change by assisting with temperature and moisture regulation. At the same time, some large coffee companies are investing millions in tree-planting efforts to meet their climate goals via carbon credits.  

 Researchers wanted to understand just how much carbon is stored in coffee farming landscapes and evaluate how carbon and biodiversity could change through tree planting or the removal of shade trees.   

The researchers gathered data from 67 scientific studies conducted in coffee regions around the world. They examined farms across a spectrum—from bare “sun coffee” monocultures with no trees at all to complex agroforestry systems where coffee grows under a canopy of native forest trees. The researchers compared the carbon stored in each type of farm, then applied these measurements to existing data on global coffee growing that shows 41% is grown in full sun, 35% with minimal shade and 24% under diverse tree cover. Finally, the team modeled what might happen under various scenarios—calculating the maximum possible carbon gains if every sun farm planted trees, and the potential losses if farms cut down existing shade trees.   

The study estimated coffee farms currently store 482 million metric tons of carbon above ground. The modeled scenarios revealed that even if all sun coffee farms added shade trees, they would sequester only 82–87 million additional metric tons of carbon. In contrast, if all shade-grown coffee were converted to monocultures, 174–221 million metric tons of carbon could be released into the atmosphere.   

 These extreme scenarios expose a fundamental issue with current carbon-market incentives for coffee farms: Mature shade trees store more carbon than newly planted trees, yet only new trees are incentivized via carbon markets. Prioritizing tree-planting above conserving existing shade trees could undermine the effectiveness of the coffee industry’s investments in climate solutions.  

 “If we don’t prioritize biodiversity on carbon sequestration projects, it won’t accidentally happen,” Pappo said. “This means choosing a diverse suite of shade trees with the aim of conserving biodiversity.”  

 To maximize the potential of coffee farming to fight climate change and boost biodiversity, the study authors call for creating carbon payment programs that reward protecting existing shade trees and ensuring these payments are accessible to small farms. For tree-planting efforts, researchers recommend explicitly prioritizing tree diversity in all planting initiatives to support biodiversity. Without these changes, global coffee agriculture may continue to lose carbon and biodiversity despite investments in tree planting.  

 Going forward, Smithsonian researchers are continuing to develop the Shade Catalog, a resource to help coffee farmers select shade trees that work well alongside coffee while providing benefits to wildlife and ecosystem services. Bird Friendly-affiliated researchers are also working on tools to help farmers find the balance between carbon storage, biodiversity and farm productivity.

Tree canopy on shade-grown coffee farms helps mitigate impacts of climate change by lowering ground temperatures and maintaining moisture levels. 

Credit

Roshan Patel, Smithsonian’s National Zoo and Conservation Biology Institute.

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Journal

Communications Earth & Environment

DOI

10.1038/s43247-025-02574-w 

Method of Research

Literature review

Subject of Research

Not applicable

Article Title

Carbon payment strategies in coffee agroforests shape climate and biodiversity outcomes

Article Publication Date

19-Aug-2025

For the First Time, Genetically Modified Trees Have Been Planted in a U.S. Forest

Gabriel Popkin
Fri, February 17, 2023 

A hand-planting crew plants poplar trees in Vidalia, Ga., Feb. 13, 2023. (Audra Melton/The New York Times)

On Monday, in a low-lying tract of southern Georgia’s pine belt, a half-dozen workers planted row upon row of twig-like poplar trees.

These weren’t just any trees, though: Some of the seedlings being nestled into the soggy soil had been genetically engineered to grow wood at turbocharged rates while slurping up carbon dioxide from the air.

The poplars may be the first genetically modified trees planted in the United States outside of a research trial or a commercial fruit orchard. Just as the introduction of the Flavr Savr tomato in 1994 introduced a new industry of genetically modified food crops, the tree planters Monday hope to transform forestry.

Living Carbon, a San Francisco-based biotechnology company that produced the poplars, intends for its trees to be a large-scale solution to climate change.

“We’ve had people tell us it’s impossible,” Maddie Hall, the company’s co-founder and CEO, said of her dream to deploy genetic engineering on behalf of the climate. But she and her colleagues have also found believers — enough to invest $36 million in the 4-year-old company.

The company has also attracted critics. The Global Justice Ecology Project, an environmental group, has called the company’s trees “growing threats” to forests and expressed alarm that the federal government allowed them to evade regulation, opening the door to commercial plantings much sooner than is typical for engineered plants.

Living Carbon has yet to publish peer-reviewed papers; its only publicly reported results come from a greenhouse trial that lasted just a few months. These data have some experts intrigued but stopping well short of a full endorsement.

“They have some encouraging results,” said Donald Ort, a University of Illinois geneticist whose plant experiments helped inspire Living Carbon’s technology. But he added that the notion that greenhouse results will translate to success in the real world is “not a slam dunk.”

🌳🌳

Living Carbon’s poplars start their lives in a lab in Hayward, California. There, biologists tinker with how the trees conduct photosynthesis, the series of chemical reactions plants use to weave sunlight, water and carbon dioxide into sugars and starches. In doing so, they follow a precedent set by evolution: Several times over Earth’s long history, improvements in photosynthesis have enabled plants to ingest enough carbon dioxide to cool the planet substantially.

While photosynthesis has profound impacts on the Earth, as a chemical process it is far from perfect. Numerous inefficiencies prevent plants from capturing and storing more than a small fraction of the solar energy that falls onto their leaves. Those inefficiencies, among other factors, limit how fast trees and other plants grow, and how much carbon dioxide they soak up.

Scientists have spent decades trying to take over where evolution left off. In 2019, Ort and his colleagues announced that they had genetically hacked tobacco plants to photosynthesize more efficiently. Normally, photosynthesis produces a toxic byproduct that a plant must dispose of, wasting energy. The Illinois researchers added genes from pumpkins and green algae to induce tobacco seedlings to instead recycle the toxins into more sugars, producing plants that grew nearly 40% larger.

That same year, Hall, who had been working for Silicon Valley ventures like OpenAI (which was responsible for the language model ChatGPT), met her future co-founder Patrick Mellor at a climate tech conference. Mellor was researching whether trees could be engineered to produce decay-resistant wood.

With money raised from venture capital firms and Hall’s tech-world contacts, including OpenAI CEO Sam Altman, she and Mellor started Living Carbon in a bid to juice up trees to fight climate change. “There were so few companies that were looking at large-scale carbon removal in a way that married frontier science and large-scale commercial deployment,” Hall said.

They recruited Yumin Tao, a synthetic biologist who had previously worked at the chemical company DuPont. He and others retooled Ort’s genetic hack for poplar trees. Living Carbon then produced engineered poplar clones and grew them in pots. Last year, the company reported in a paper that has yet to be peer reviewed that its tweaked poplars grew more than 50% faster than non-modified ones over five months in the greenhouse.

The company’s researchers created the greenhouse-tested trees using a bacterium that splices foreign DNA into another organism’s genome. But for the trees they planted in Georgia, they turned to an older and cruder technique known as the gene gun method, which essentially blasts foreign genes into the trees’ chromosomes.

In a field accustomed to glacial progress and heavy regulation, Living Carbon has moved fast and freely. The gene gun-modified poplars avoided a set of federal regulations of genetically modified organisms that can stall biotech projects for years. (Those regulations have since been revised.) By contrast, a team of scientists who genetically engineered a blight-resistant chestnut tree using the same bacterium method employed earlier by Living Carbon have been awaiting a decision since 2020. An engineered apple grown on a small scale in Washington state took several years to be approved.

“You could say the old rule was sort of leaky,” said Bill Doley, a consultant who helped manage the Agriculture Department’s genetically modified organism regulation process until 2022.

On Monday, on the land of Vince Stanley, a seventh-generation farmer who manages more than 25,000 forested acres in Georgia’s pine belt, mattock-swinging workers carrying backpacks of seedlings planted nearly 5,000 modified poplars. The tweaked poplars had names like Kookaburra and Baboon, which indicated which “parent” tree they were cloned from, and were interspersed with a roughly equal number of unmodified trees. By the end of the unseasonably warm day, the workers were drenched in sweat and the planting plots were dotted with pencil-thin seedlings and colored marker flags poking from the mud.

In contrast to fast-growing pines, hardwoods that grow in bottomlands like these produce wood so slowly that a landowner might get only one harvest in a lifetime, Stanley said. He hopes Living Carbon’s “elite seedlings” will allow him to grow bottomland trees and make money faster. “We’re taking a timber rotation of 50 to 60 years and we’re cutting that in half,” he said. “It’s totally a win-win.”

Forest geneticists were less sanguine about Living Carbon’s trees. Researchers typically assess trees in confined field trials before moving to large-scale plantings, said Andrew Newhouse, who directs the engineered chestnut project at SUNY College of Environmental Science and Forestry. “Their claims seem bold based on very limited real-world data,” he said.

Steve Strauss, a geneticist at Oregon State University, agreed with the need to see field data. “My experience over the years is that the greenhouse means almost nothing” about the outdoor prospects of trees whose physiology has been modified, he said. “Venture capitalists may not know that.”

Strauss, who previously served on Living Carbon’s advisory board, has grown some of the company’s seedlings since last year as part of a field trial funded by the company. He said the trees were growing well, but it was still too early to tell whether they were outpacing unmodified trees.

Even if they do, Living Carbon will face other challenges unrelated to biology. While outright destruction of genetically engineered trees has dwindled thanks in part to tougher enforcement of laws against acts of ecoterrorism, the trees still prompt unease in the forestry and environmental worlds. Major organizations that certify sustainable forests ban engineered trees from forests that get their approval; some also prohibit member companies from planting engineered trees anywhere. To date, the only country where large numbers of genetically engineered trees are known to have been planted is China.

The U.S. Forest Service, which plants large numbers of trees every year, has said little about whether it would use engineered trees. To be considered for planting in national forests, which make up nearly one-fifth of U.S. forestland, Living Carbon’s trees would need to align with existing management plans that typically prioritize forest health and diversity over reducing the amount of atmospheric carbon, said Dana Nelson, a geneticist with the service. “I find it hard to imagine that it would be a good fit on a national forest,” Nelson said.

Living Carbon is focusing for now on private land, where it will face fewer hurdles. Later this spring it will plant poplars on abandoned coal mines in Pennsylvania. By next year Hall and Mellor hope to be putting millions of trees in the ground.

🌳🌳🌳

To produce an income stream not reliant on venture capital, the company has started marketing credits based on carbon its trees will soak up. But carbon credits have come under fire lately and the future of that industry is in doubt.

And to head off environmental concerns, Living Carbon’s modified poplar trees are all female, so they won’t produce pollen. While they could be pollinated by wild trees and produce seeds, Mellor says they’re unlikely to spread into the wild because they don’t breed with the most common poplar species in the Southeast.

They’re also being planted alongside native trees like sweet gum, tulip trees and bald cypress, to avoid genetically identical stands of trees known as monocultures; non-engineered poplars are being planted as experimental controls. Hall and Mellor describe their plantings as both pilot projects and research trials. Company scientists will monitor tree growth and survival.

Such measures are unlikely to assuage opponents of genetically modified organisms. Last spring, the Global Justice Ecology Project argued that Living Carbon’s trees could harm the climate by “interfering with efforts to protect and regenerate forests.”

“I’m very shocked that they’re moving so fast” to plant large numbers of modified trees in the wild, said Anne Petermann, the organization’s executive director. The potential risks to the greater ecosystem needed to be better understood, she said.

Ort of the University of Illinois dismissed such environmental concerns. But he said investors were taking a big chance on a tree that might not meet its creators’ expectations.

“It’s not unexciting,” he said. “I just think it’s uber high risk.”

© 2023 The New York Times Company

Mysterious living monuments

How will the biggest tropical trees respond to climate change?

SMITHSONIAN TROPICAL RESEARCH INSTITUTE

VIDEO: INTERVIEW WITH CO-AUTHORS EVAN GORA, POST DOCTORAL FELLOW, SMITHSONIAN TROPICAL RESEARCH INSTITUTE AND ADRIANE ESQUIVEL-MUELBERT, LECTURER AT THE UNIVERSITY OF BIRMINGHAM, UK. AVAILABLE WITH SPANISH SUBTITLES ON REQUEST. view more 

CREDIT: SMITHSONIAN TROPICAL RESEARCH INSTITUTE

Giant trees in tropical forests, witnesses to centuries of civilization, may be trapped in a dangerous feedback loop according to a new report in Nature Plants from researchers at the Smithsonian Tropical Research Institute (STRI) in Panama and the University of Birmingham, U.K. The biggest trees store half of the carbon in mature tropical forests, but they could be at risk of death as a result of climate change--releasing massive amounts of carbon back into the atmosphere.

Evan Gora, STRI Tupper postdoctoral fellow, studies the role of lightning in tropical forests. Adriane Esquivel-Muelbert, lecturer at the University of Birmingham, studies the effects of climate change in the Amazon. The two teamed up to find out what kills big tropical trees. But as they sleuthed through hundreds of papers, they discovered that nearly nothing is known about the biggest trees and how they die because they are extremely rare in field surveys.

"Big trees are hard to measure," said Esquivel-Muelbert. "They are the pain in a field campaign because we always have to go back with a ladder to climb up to find a place to measure the circumference above the buttresses. It takes a long time. Studies focusing on the reasons trees die don't have enough information for the biggest trees and often end up excluding them from their analysis."

"Because we generally lack the data necessary to tell us what kills trees that are above approximately 50 centimeters in diameter, that leaves out half of the forest biomass in most forests," Gora said.

Only about 1% of trees in mature tropical forests make it to this size. Others wait their turn in the shade below.

The other thing that makes tropical forests so special--high biodiversity--also makes it difficult to study big trees: There are so many different species, and many of them are extremely rare.

"Because only 1-2% of big trees in a forest die every year, researchers need to sample hundreds of individuals of a given species to understand why they are dying," Gora said. "That may involve looking for trees across a huge area."

Imagine a study of blood pressure in people who have lived to be 103. One would have to locate and test seniors from cities and towns around the world: a time-consuming, logistically complex and expensive proposition.

A large body of evidence shows that trees are dying faster in tropical forests than ever before. This is affecting the ability of forests to function and in particular, to capture and store carbon dioxide.

"We know the deaths of largest and oldest trees are more consequential than the death of smaller trees," Gora said. "Big trees may be at particular risk because the factors that kill them appear to be increasing more rapidly than the factors that seem to be important for smaller-tree mortality."

In large parts of the tropics, climate change is resulting in more severe storms and more frequent and intense droughts. Because big trees tower above the rest, they may be more likely to be hit by lightning, or damaged by wind. Because they have to pull ground water higher than other trees, they are most likely to be affected by drought.

Hoping to better understand what is happening to big trees, Gora and Esquivel-Muelbert identified three glaring knowledge gaps. First, almost nothing is known about disease, insects and other biological causes of death in big trees. Second, because big trees are often left out of analyses, the relationship between cause of death and size is not clear. And, finally, almost all of the detailed studies of big tropical trees are from a few locations like Manaus in Brazil and Barro Colorado Island in Panama.

To understand how big trees die, there is a trade-off between putting effort into measuring large numbers of trees and measuring them often enough to identify the cause of death. Gora and Esquivel-Muelbert agree that a combination of drone technology and satellite views of the forest will help to find out how these big trees die, but this approach will only work if it is combined with intense, standardized, on-the-ground observations, such as those used by the Smithsonian's international ForestGEO network of study sites.

Esquivel-Muelbert hopes that the impetus for this research will come from a shared appreciation for these mysterious living monuments:

"I think they are fascinating to everyone," she said. "When you see one of those giants in the forest, they are so big. My colleague and Amazonian researcher, Carolina Levis, says that they are the monuments we have in the Amazon where we don't have big pyramids or old buildings....That is the feeling, that they have been through so much. They are fascinating, not just in the scientific sense but also in another way. It moves you somehow."

###

Funding for this study was from STRI, the U.S. National Science Foundation and the TreeMort project as part of the EU Framework Programme for Research and Innovation.

The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is a unit of the Smithsonian Institution. The institute furthers the understanding of tropical biodiversity and its importance to human welfare, trains students to conduct research in the tropics and promotes conservation by increasing public awareness of the beauty and importance of tropical ecosystems. Promo video.

Gora, E.M. and Esquivel-Muelbert, A. 2021. Implications of size-dependent tree mortality for tropical forest carbon dynamics. Nature Plants. doi: 10.1038/s41477-021-00879-0

CAPTION

The flowery crown of Dipteryx oleifera, one of the biggest trees on Barro Colorado Island, Panama, towers above the forest. Big trees may be most exposed to the effects of climate change: more frequent and severe drought, and the high winds and lightning of monster storms.

CREDIT

Evan Gora, STRI

CAPTION

Measuring the largest rainforest trees requires carrying a ladder out into the jungle, often to hard-to-access sites. Long term forest monitoring plots such as the Smithsonian's ForestGEO network use standard techniques to measure giant trees. However, in remote areas, researchers may decide to leave the biggest trees out of their studies, because it is too time-consuming to measure them.

CREDIT

Sean Mattson, STRI

 

How changing L.A.’s tree rules could cool more neighborhoods

A new USC Dornsife study finds that outdated guidelines are limiting tree growth — especially in lower-income neighborhoods — and offers a path forward.

University of Southern California

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Expansive tree canopies are crucial for healthy ecosystems and livable cities. Yet, Los Angeles’ strict tree planting rules, originally meant to protect infrastructure and public safety, are now widening shade disparities, particularly in lower-income neighborhoods. A new study published in Landscape and Urban Planning, led by the Spatial Sciences Institute and Public Exchange, both based at the USC Dornsife College of Letters, Arts and Sciences, suggests that easing these decades-old restrictions could significantly grow the city’s urban tree canopy — without compromising safety.

This research builds on an earlier USC study comparing L.A.’s municipal codes, engineering standards and urban forestry guidelines to those of 25 other cities — 17 outside California and eight within the state. That study found L.A.’s tree placement rules are among the nation’s strictest, often limiting new planting. The team concluded that substantial changes could be made to existing tree-spacing guidelines without re-writing laws, but better coordination between city departments is essential.

“Fixing L.A.’s rules is a step toward addressing inequities and bringing the health and ecological benefits of green infrastructure to underserved communities,” said Laura Messier, PhD candidate in the population, health and place program at the Spatial Sciences Institute.

Testing looser tree spacing rules

To test how relaxing planting guidelines might increase tree coverage, Messier and her team compared two L.A. neighborhoods: Boyle Heights, a historically lower-income area east of downtown; and Studio City, a wealthier community in the San Fernando Valley. Both areas studied were similar in size, topography and parcel layout. But Studio City had about 3,020 trees per square mile, compared to 2,183 in Boyle Heights — a gap researchers linked to the neighborhood’s denser street grid, higher concentration of multi-family housing and smaller parcels, all of which limit where trees can be planted.

Using mapping software, the team identified obstacles like utility poles, gas lines and bus stops, then modeled potential new planting sites. They compared L.A.’s current planting restrictions with more flexible guidelines in other California cities — including San Francisco, Fremont, Oakland and Anaheim — and identified infrastructure changes that could further expand tree coverage.

The results were striking. Under L.A.’s current rules, Studio City could support up to 140 trees per square mile, while Boyle Heights maxed out at 121. But with looser guidelines, the gap nearly vanished — Studio City’s capacity rose to 158, while Boyle Heights jumped to 153, a 26% increase in the historically Latino neighborhood.

Still, Boyle Heights faces challenges beyond planting guidelines. Narrow sidewalks limit the ability to plant large shade trees. Even with the same number of trees, only 34.5% in Boyle Heights could be large-canopy species, compared to 61% in Studio City.

Small tweaks to tree spacing make big impact

Even modest policy changes could open up more space for tree planting in crowded areas.

The study found that easing restrictions near intersections could increase the number of trees in Boyle Heights by 7.6%, while relaxing rules around utility poles could add another 5.5%. Adjusting guidelines for gas lines (2.6%), streetlights (2.2%), driveways (1.4%) and other infrastructure could push the total canopy gain to 26%, helping expand shade in other dense, lower-income neighborhoods.

While planting trees at bus stops would add less than 1% to overall canopy coverage, it could make a big difference for transit riders exposed to extreme summer heat.

A major obstacle to planting more trees is L.A.’s 45-foot visibility rule at intersections, last updated in 1988. Studies show high-canopy trees don’t block drivers’ views, making this restriction ripe for revision.

Easier to change tree spacing rules than laws

Many of the restrictions are internal guidelines rather than laws, meaning changes could be implemented more easily. The city’s Urban Forestry Division would need to update its Tree Spacing Guidelines memo, but getting agreement from other departments — such as transportation and street lighting — could still be a challenge, Messier explained.

Ironically, the study found that half the street trees in Boyle Heights and nearly 40% in Studio City don’t comply with city guidelines. Yet, there’s little evidence that these violations create safety or liability issues.

Messier suggests that updating the guidelines is more practical than enforcing rules that are often ignored and seem to have little impact on safety.

While modernizing L.A.’s rules is an important step, closing the shade gap will require broader infrastructure changes. Messier and her team point to strategies like reducing street widths — known as “road diets” — to create more space for trees.

“To truly close the shade gap and ensure more equitable access to cooling and green spaces, the city must invest in infrastructure that makes room for more trees in underserved areas,” Messier said.

 

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Journal

Landscape and Urban Planning

DOI

10.1016/j.landurbplan.2025.105345 

Method of Research

Case study

Subject of Research

Not applicable

Article Title

Equity impacts of street tree spacing guidelines: A case study in two Los Angeles neighborhoods

Article Publication Date

25-Mar-2025

Getting hit by lightning is good for some tropical trees

Cary-led study reveals lightning benefits some trees by killing off parasitic vines and opening up the canopy

Cary Institute of Ecosystem Studies

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Technician Cesar Gutierrez climbs a tower to detect and locate lightning strikes in the study area. After detection, drones and on-the-ground teams monitor the strike’s impacts.

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Credit: Evan Gora / Cary Institute of Ecosystem Studies

Getting zapped with millions of volts of electricity may not sound like a healthy activity, but for some trees, it is. A new study, published in New Phytologist, reports that some tropical tree species are not only able to tolerate lightning strikes, but benefit from them. The trees may have even evolved to act as lightning rods.

The research was led by Evan Gora, a forest ecologist at Cary Institute of Ecosystem Studies. Gora studies how lightning impacts biodiversity and carbon storage in Panama’s tropical forests. 

Lightning kills hundreds of millions of trees per year. But in 2015, while working in Panama, Gora and his colleagues came across a Dipteryx oleifera tree that had survived a strike with little damage — even though the jolt had been strong enough to blast a parasitic vine out of its crown and kill more than a dozen neighboring trees.  

“Seeing that there are trees that get struck by lightning and they’re fine was just mind-blowing,” Gora recalled. Over time, the team encountered other Dipteryx oleifera trees thriving after getting hit, so they decided to take a closer look.

Scientists had previously suspected that some trees evolved to tolerate lightning, but evidence to back it up was lacking. In 2022, Gora and colleagues demonstrated for the first time that trees differ in their ability to survive getting hit by lightning. Their new paper, published Wednesday, is the first to show that trees can benefit from these electric jolts. 

Using a unique lightning location system, the team tracked the outcomes of 93 trees that had been struck by lightning in Barro Colorado Nature Monument in central Panama. For two to six years after the strike, the team measured tree survival rates, crown and trunk condition, number of parasitic vines or lianas, and neighboring tree mortality. The study included nine directly struck Dipteryx oleifera trees, and compared them with 84 other trees that had been struck. 

All nine Dipteryx trees survived direct lightning strikes with only minor damages. In contrast, directly struck trees of other species were badly damaged, losing 5.7 times more leaves from their crowns, and 64% died within two years. 

When each Dipteryx tree was zapped, an average of 9.2 neighboring trees were killed as the electricity traveled between adjoining vines and touching branches, or jumped across small gaps between trees. Lightning strikes also reduced Dipteryx liana infestations by 78%, freeing trees from some of the pressure these parasitic vines have on light and nutrient availability.

These patterns also bore out across the broader population. The team found that Dipteryx trees tend to have fewer lianas. Analyzing trends in tree death over the past 40 years, the researchers found that the trees neighboring Dipteryx trees were 48% more apt to die than other trees in the forest, likely because of lightning. 

Using drones, Gora and colleagues created 3D models of canopy height, which showed that Dipteryx trees tend to be about four meters taller than their nearest neighbors, likely because lightning killed their taller neighbors, giving them an advantage in competing for light and space. 

“These data provide the first evidence that some trees benefit from being struck by lightning,” the authors write. Or, as Gora puts it, “It's better off for a Dipteryx oleifera tree to be struck than not.”

Because of all these benefits, Dipteryx oleifera trees may be specially adapted to attract lightning. With their distinctive height and unusually wide crowns, they may be up to 68% more likely to get electrocuted than other trees with average height and crowns, according to the team’s calculations. 

Estimates suggest individual Dipteryx oleifera trees are directly hit by lightning every 56 years, on average. And since the trees can live for hundreds or possibly more than a thousand years, they are expected to survive these blasts many times throughout their lives. During the study, one of the Dipteryx trees was struck twice in just five years. 

The remarkable ability to survive lightning strikes and benefit from the removal of lianas and competitors gives Dipteryx trees a major advantage over other trees. According to the scientists' calculations, lightning tolerance boosts the species’ ability to produce offspring by 14 times. 

Next, the team aims to investigate what electrical or structural traits allow these trees to survive lightning strikes. They would also like to explore whether other species show lightning tolerance, to better understand how common this phenomenon is. 

What is clear is that lightning plays an underappreciated role in tree competition. And with lightning on the rise in many regions due to climate change, its influence may increase, potentially favoring lightning-tolerant species like Dipteryx oleifera. Understanding lightning and its role in shaping forests may be important for predicting changes in biodiversity and carbon storage, and for informing tropical reforestation efforts. 

A Dipteryx oleifera tree just after being struck by lightning in 2019 (left) versus two years later (right). The tree survived the strike with minimal damage, and benefited from having its parasitic vines and competing neighbors removed by the strike. 

Also known as the eboe, choibá, tonka bean or almendro, Dipteryx oleifera is native to Honduras, Nicaragua, Costa Rica, Panama, Colombia, and Ecuador. Its hard wood is used in construction, and it produces almond-flavored seeds that are edible and sold in local markets. A keystone species of Panamanian forests, D. oleifera fruits and seeds are a crucial food source for rainforest mammals such as agouti during the dry season.

Credit

Evan Gora / Cary Institute of Ecosystem Studies

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Study co-authors include: Helene Muller-Landau and Pablo Narváez of the Smithsonian Tropical Research Institute; KC Cushman of Oak Ridge National Laboratory; Jeannine Richards of Florida Gulf Coast University; Phillip Bitzer and Jeffrey Burchfield of the University of Alabama in Huntsville; and Stephen Yanoviak of the University of Louisville.

This work was supported by grants from the National Science Foundation (DEB-1354060, DEB-1655346, and DEB-2213246 to SPY, DEB-1354510, DEB-1655554, and DEB-2213247 to PMB, and DEB-2213245, DEB-2241507, and GRF-2015188266 to EMG), the National Geographic Society (9703-15 to EMG), and a Smithsonian Tropical Research Institute Tupper Postdoctoral Fellowship to EMG. KCC was supported as part of the Next Generation Ecosystem Experiments-Tropics, funded by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research.

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Cary Institute of Ecosystem Studies is an independent nonprofit center for environmental research. Since 1983, our scientists have been investigating the complex interactions that govern the natural world and the impacts of climate change on these systems. Our findings lead to more effective resource management, policy actions, and environmental literacy. Staff are global experts in the ecology of: cities, disease, forests, soils, and freshwater.

New Phytologist is a leading international journal focusing on high quality, original research across the broad spectrum of plant sciences, from intracellular processes through to global environmental change. The journal is owned by the New Phytologist Foundation, a not-for-profit organisation dedicated to the promotion of plant science.

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Journal

New Phytologist

DOI

10.1111/nph.70062 

Article Title

How some tropical trees benefit from being struck by lightning: evidence for Dipteryx oleifera and other large-statured trees

Article Publication Date

26-Mar-2025