By Ronnie Siegel

The Wildland Urban Interface (WUI) is the area where the built environment meets wildlands. We can reduce the risk of WUI wildfires with a landscape approach. This involves understanding the increased risks of climate change, the condition of wildland ecosystems, and the condition of trees, plants, and buildings in developed areas.

Significant fieldwork, reviews of data mapping, and communication with eye witnesses yield convincing evidence that trees and plants didn’t cause the spread of the Eaton fire in Los Angeles County, California. In fact, they have the potential to reduce the spread of future urban wildfires.

Climate change has increased the risk of WUI wildfires. This finding is explained in much more detail by climate scientist Daniel Swain. He explains that in Southern California, climate models suggest global temperature rise doesn’t lead to a change in mean precipitation, but rather a shift to a more extreme delivery of that precipitation – longer periods with no rain and more intense rainfall when it does arrive.

Dry seasons get hotter, drier, and longer, pulling moisture out of the soils and plants through increased evaporation and transpiration. When the rain arrives, it’s more intense. This extreme hydro-climatic whiplash pushes wildland vegetation to higher drought level conditions well into November to January when offshore Santa Ana winds arrive, often at hurricane force. In the Town of Altadena, an unincorporated area in Los Angeles County, the risk of this deadly combination has increased 36 percent since the 1980’s and will likely increase more as global warming progresses.

To reduce long-term wildfire risk, we obviously need to lower our greenhouse gas emissions and sequester more carbon. And to reduce short-term risk using a landscape approach, we should stop development in the WUI, inhibit wildland fires from reaching urban developments using vegetated buffer zones, and make urban environments more fire resistant.

For fire resistance, we can reduce risk at the micro-scale – individual homeowner’s property – by “home hardening” and using defensible space strategies that act to reduce fire spread. And at the macro-scale – the level of the community – we can use land-use planning to create buffers between wildlands and urban landscapes and provide access for firefighters to reduce the risk of wildfire spread.

The Causes of the Eaton Fire

This winter followed the hottest summer on record, with no significant rainfall since April 2024. The chaparral plants in the San Gabriel hills above the town of Altadena were parched. At the same time, Santa Ana winds arrived in an extreme force gusting up to 100 miles an hour. On January 7, this worst-case wildfire scenario arrived – the Eaton fire had ignited.

The ignition appears to have been caused by a spark from power lines, probably caused by the winds, which then ignited the tinder-dry plants below. Anecdotal accounts by residents found that in the first 15 minutes after the fire started, the wind blew embers almost a mile from the ignition point, starting additional fires.

To complicate matters: during the progression of the fire, the winds generally blew southwest over the mountains and towards the ocean. But locally in the fire area, the winds blew in all directions at times, carrying embers that would ignite homes, the most flammable objects in their path.

Ty Garrison, a local resident and biologist, stayed during the wildfire to try to save his home. He captured on video tall palm trees blowing east while trashcans blew west, with embers flying everywhere. He witnessed some plants defusing embers and others, like bamboo, spreading more. Firefighting from the air was too dangerous in heavy winds, so there were only ground crews deployed in the most dangerous conditions – high winds, toxic smoke, and a water supply that didn’t last.

With thousands of homes burning at once – ultimately over 9,000 structures – the water infrastructure, which was never designed to handle that many home fires at one time, ran dry in many areas. During the first night and into the morning of the Eaton fire, the fire had spread several miles in many directions from the ignition point, primarily from wind-driven embers and in some areas closely-spaced, flammable homes, igniting each other through radiant heat and flame contact.

The Role of Trees and Plants

Post-fire observation of this disaster reveals that among the ashes of entire homes and charred cars, trees, shrubs, and even lawns survived. And today, trees are making a remarkable recovery.

Scientific studies, including one by assistant professor Alessandro Ossola at the University of California at Davis, are documenting tree casualty and recovery using LiDAR imaging. A group of Altadena arborists along with landscape architect Stephanie Landregan, FASLA, fought to preserve trees unnecessarily scheduled for removal by the U.S. Army Corp of Engineers during the home debris removal phase.

It is evident that urban trees and plants didn’t cause the spread of this fire. The homes themselves, along with cars, were the most combustible part of the landscape. This was seen in satellite views of the nighttime city. Even trees that are considered highly flammable, like pines and deodars, were standing unharmed with green needles after the fire scorched their bark. Their fire damage came from being too near burning homes rather than from embers. When trees were found burned, they were usually surrounded by burned homes on all sides or multiple cars.

Deciduous trees were leafless at the time of the fire, possibly making them less flammable. Native sycamores did very well along with other non-native deciduous trees. Evergreen trees – such as the native fire-adapted coast live oak and pine species that were native to other fire-adapted plant communities – and non-native evergreen deodars, did exceptionally well, and in some cases appear to have shielded homes from embers.

Several homes that were not adequately “home hardened” survived because they appeared to be shielded from embers by surrounding native oaks. Eyewitness accounts recall evergreen canopies of deodar trees acting as umbrellas over homes intercepting and diffusing embers.

How did they perform this feat? The answer lies in the plant’s ability to hold water. Native plants and ones that are adapted to withstand drought or fire can retain water very well without extra irrigation. Deep-rooted trees are less affected by soil surface evaporation, and many irrigated plant species perform well with artificially supplied water.

A study of the water holding capacity of various plant species in branches and leaves and needles may be one good way to predict their fire resistance. Native and non-native species survived, and their water holding capacity seemed to protect them from burning.

Potential Solutions for the Next Wildfire

On a micro-scale, “home hardening” – the process of building or renovating homes to create a fire protective shell – should be the focus of rebuilding efforts. It’s the best strategy for protecting homes in the WUI.

Defensible space guidelines are another important strategy. They provide recommendations on landscape treatment in zones surrounding a building – zone 0 is the 5-foot perimeter around the building, zone 1 is the distance of 5-30 feet from the structure, and zone 2 is 30-100 feet. These guidelines currently recommend generous separation between trees and shrubs to prevent fire ladders and canopy fire spread. There appeared to be little of this type of fire spread in the plants of the Eaton fire, and defensible space guidelines may need to be reviewed and amended.

Local fuel modification plan guidelines in Los Angeles County recommend types of plants suitable to each zone and are required to be followed to permit new construction. This plant list should also be updated to correct discrepancies found in post-fire observation where many “flammable” species performed as ember shields and did not burn. Observations indicate plant species that are fire-adapted and hold water during drought are ideal.

However, ensuring even drought-tolerant plants get just enough supplemental water during exceptional dry years is important. Making sure the ground cover and soil has good capacity to hold moisture can keep embers from igniting. Planting native species has the dual benefit of promoting biodiversity.

On a macro-scale: a recent NASA satellite multispectral composite image comparing vegetation before and after the fire seems to indicate that the chaparral vegetation burned more intensely and completely than vegetation in the developed area, including plants around burned homes. This is most likely due to supplemental irrigation.

Also, looking at post-fire aerial maps and satellite images, there are possible indications that the right trees in urban green spaces can act as buffer zones limiting the spread of fire.

An example of this is a 0.7 mile-long double row of 140 year old cedrus deodara street trees on Santa Rosa Avenue, which form an almost continuous canopy.

Against expectations and defying defensible space guidelines – which identify this tree as flammable and a hazard when planted in continuous canopy rows – this double row had no tree loss. All structures under them and on their leeward side were preserved (except for three at the very end of the row in the heart of the burned area). Coincidentally, a golf course and cemetery, mostly lawn and trees each 0.25 mile long by 0.4 mile wide at the perimeter of the fire may have slowed or even stopped the fire’s spread.

Can plants predictably protect buildings from burning? Can vegetative buffer zones make a difference, and, if so, how large should they be and what type of planting works best? What modifications need to be made to the current defensible space guidelines?

It is difficult to reach conclusions. Variables that affected the fire’s spread include:

• Topography
• Wind force and direction that constantly changed
• Wind barriers such as block walls, buildings, or plants that resisted ignition
• Homes that were built to resist embers, radiant heat and flames vs homes that were not designed to be resilient
• Homes that had well irrigated plants vs ones that were dry
• Home landscapes that were well maintained vs those that had a lot of dead vegetation or flammable furniture, cars, or debris
• Embers that by chance fell on flammable buildings or objects
• Efforts by residents hosing down embers during the fire
• And efforts by firefighters battling the fire with water and using other interventions

In post-fire observations, all of these factors complicate conclusions about buffer zones and defensible space guidelines. What is needed is collaboration between CalFire, the Los Angeles County Fire Department, front line firefighters, residents, architects, landscape architects, fire scientists, and planners to pour over maps and discuss the variables. Together, we can reassess the post-fire evidence. With a more in depth assessment and continued fire science research to test plant flammability, we can update recommended plant lists, perfect the defensible space guidelines, and plan vegetated buffer zones. Then we would be better able to reduce our collective wildfire risk.

Ronnie Siegel, ASLA, is founder of Swire Siegel Landscape Architects, author of  Towards Zero Emission Business Operations: A Landscape Architect’s Guide to Reducing the Climate Impacts of Offices, and a member of the ASLA Climate and Biodiversity Action Committee.

Extreme heat, flooding, drought, sea level rise, wildfire, air and water pollution, and ecosystem loss and degradation transcend state and national borders and demand collective solutions.

ASLA and its 16,000 members will remain a leader in shaping science-based climate and biodiversity solutions that protect American and global health and well-being.

• At the local and state levels: ASLA will continue to lead efforts to make our communities and ecosystems healthier and more resilient through nature-based solutions. ASLA will remain a member of the America Is All In movement, which is dedicated to achieving the goals of the Paris Climate Agreement.
• At the global level: ASLA will continue to advance our members’ climate and biodiversity goals as an observer to the UN Framework Convention on Climate Change (UNFCCC) – and participation in the UN Convention on Biological Diversity, International Federation of Landscape Architects (IFLA), and other international organizations.

ASLA is committed to increasing investment in nature-based solutions locally, nationally, and internationally – action that is required to ensure the health of future generations and ecosystems.

The Value of Nature-Based Solutions

Nature-based solutions are infrastructure that use, restore, or emulate natural ecological processes and can be created through a design process.

Examples include:

• Floodplains
• Living shorelines
• Beaches
• Dunes
• Wetlands
• Reefs
• Islands
• Green roofs
• Tree canopies
• Rain gardens
• Bioswales
• Retention basins
• Permeable and pervious pavements

Their construction costs can be up to 30 percent less and their maintenance costs up to 25 percent less than conventional gray infrastructure. They are crucial to creating healthy communities that are better prepared for long-term heat, flooding, and other challenges and natural disasters.

Landscape architects are the only design professionals specifically educated and trained to develop nature-based solutions that address a range of community health, biodiversity, and economic challenges.

ASLA has produced important research – Landscape Architecture: Maximizing Economic Benefits of Nature-Based Solutions – that documents the economic effectiveness of designing with nature.

These solutions have been proven time and again to strengthen local economies, encourage new development, increase property values, reduce insurance risks and costs, and create good paying jobs that can’t be outsourced – in all communities across the nation.

ASLA research has found that in the United States:

• Sustainable design can create nearly 20 million jobs in grounds maintenance, sustainable urban planning development, renewable energy, construction, and green technology.
• Investments in parks and green space can generate between $4 and $11 for every dollar invested, due to increased tourism, improved property values, and enhanced community health.
• Every dollar invested in ecosystem restoration returns $5 to $28 in benefits.
• Ecosystem services from urban green spaces provide value — from $500 to $1,600 per acre per year.

ASLA will advance nature-based approaches that increase our collective resilience, create economic benefits, and protect public health, safety, and welfare:

Community Resilience: Landscape architects play a critical role in mitigating the effects of storm severity, implementing nature-based solutions in communities to reduce billions of dollars in damages annually. These proactive measures lessen the financial burden on federal disaster aid programs while safeguarding communities.

Thriving Economies: Landscape architects design nature-based solutions that generate substantial economic returns for rural, suburban, and urban communities. These solutions also reduce risk and therefore insurance costs.

Public Health, Safety, and Welfare: Landscape architects design safe solutions that improve public health by protecting our air, water, and natural resources; cool our communities; and provide access to nature and recreation.

Get Involved

Landscape architects are essential to advancing climate and biodiversity solutions — but lasting impact requires a shared commitment. Whether you contribute your voice, your expertise, or your resources, your involvement helps shape a healthier, more resilient future.

• Look out for updates on the new ASLA Climate and Biodiversity Action Plan for 2026-2030 and support its development by sharing your insights and staying engaged.
• Invest in the future of this work with a donation. Your support will help ASLA launch the plan, drive policy change, fund research, and expand public outreach.
• Watch the ASLA Climate and Biodiversity Action 101 webinar series, which is free for ASLA members.
• Start or join your Chapter’s Climate and Biodiversity Action Committee.
• And read ASLA’s The Dirt to stay up-to-date on the latest developments on climate, biodiversity, and landscape architecture. Subscribe to the monthly newsletter.

By Diogo Borges Ferreira

Roberto Burle Marx is celebrated as a pioneering landscape architect because of his way of integrating nature into cities. His work shows a deep respect for native flora and a commitment to ecological balance.

At a time when climate change and biodiversity loss are pressing global concerns, we can revisit Burle Marx’s principles. His landscapes in Brazil demonstrate how to create urban spaces that are resilient, sustainable, functional, and beautiful. They offer valuable lessons for contemporary landscape architects.

From the 1930s to the 1990s, Burle Marx anticipated many of today’s concerns. Long before terms like sustainable design or green infrastructure became commonplace, Burle Marx advocated for native plants, recognizing their role in creating self-sustaining ecosystems that required minimal intervention. His projects often transformed neglected urban areas into vibrant, ecologically-balanced spaces. His landscapes improved the environment and enhanced the quality of life for city dwellers.

Burle Marx understood that landscapes are dynamic, ever-changing entities rather than static compositions. He emphasized the importance of designing with a long-term vision, ensuring that his landscapes could adapt to change over time, both in terms of ecological shifts and our use.

As cities grapple with the challenges of rapid urbanization, climate adaptation, and biodiversity conservation, Burle Marx’s work offers a model for how landscape architects can address these critical issues.

From his legacy, we can extract key lessons on how to:

• Design for resilience
• Prioritize native plants
• Create spaces that are deeply connected to their cultural and ecological contexts

Burle Marx viewed landscapes as living, evolving systems rather than static designs, a philosophy vividly embodied in Sítio Roberto Burle Marx in Rio de Janeiro, Brazil, his former residence that now functions as a public garden and museum.

Initially established as a plant nursery in the 1940s, the Sítio evolved into a living laboratory for botanical experimentation, showcasing over 3,500 plant species of tropical and subtropical flora. Many of these species are rare or endangered.

The Sítio demonstrates Burle Marx’s commitment to adaptive management and continuous education. It serves as a global center for research and learning that attracts botanists and landscape architects.

Its ongoing evolution underscores the importance of viewing landscapes as living entities that require adaptive management, challenging the concept of a finished landscape and highlighting the need for long-term stewardship.

Burle Marx’s adaptive approach is also evident in projects like the gardens of the Ministry of Education and Health building in Rio de Janeiro, completed in 1938.

This project underscores the role of landscape architects in adapting to change and fostering connections between people and nature. It can inspire contemporary landscape architects to prioritize adaptive management and continuous learning.

The rooftop garden, innovative for its time, features sinuous forms and vibrant colors that evoke 19th-century garden plans while reinterpreting them in a modernist context. The garden improved building insulation and mitigated the urban heat island effect. It also creates a sanctuary for biodiversity, showcasing the multifaceted benefits of integrating nature into urban architecture.

All these features contribute to the idea that urban development and nature conservation aren’t mutually exclusive. Landscapes can create emotional connections through modernist abstract forms and plants. The rooftop garden demonstrates how cities can function as complex ecosystems benefiting both people and nature.

Roberto Burle Marx’s design for Parque do Flamengo in Rio de Janeiro shows his groundbreaking approach to landscape architecture, urban planning, and the preservation of local biodiversity and cultural identity.

Developed in the 1960s, it was conceived as an urban garden that transitions between the sea, city, and mountains. The park provides versatile spaces for recreation, leisure, and cultural activities. Spanning 1.2 million square meters, Flamengo Park transformed a former landfill into a vibrant urban ecosystem, featuring over 17,000 trees from 240 species.

By prioritizing native Brazilian species, Burle Marx preserved the local ecological identity. He promoted biodiversity by providing habitats for local fauna and creating plants adapted to local climate conditions requiring less water and maintenance. He also strengthened cultural connections to the land crafting spaces that are distinctly Brazilian. This approach was instrumental in Rio de Janeiro becoming the first city in the world to earn UNESCO World Heritage status as an Urban Cultural Landscape in 2012.

Another defining feature of Parque do Flamengo is how Burle Marx’s landscape design acts as the unifying element that ties together the various architectural landmarks within the site, including the Monumento aos Mortos da Segunda Guerra Mundial, the Marina da Glória, and the Museu de Arte Moderna. By integrating landscape and architecture, he underscores the role of outdoor spaces as vital connectors within the urban fabric, enhancing the city’s identity and function.

Through this, Burle Marx set a powerful precedent for contemporary landscape architects and urban planners, showing how urban landscapes can serve as dynamic repositories of biodiversity and cultural heritage. He created spaces that are ecologically significant and deeply connected to the residents and their local environment.

Roberto Burle Marx’s work on the Copacabana Beach Promenade and the Conjunto Residencial Prefeito Mendes de Moraes (Pedregulho) shows his ability to blend function, aesthetics, and cultural heritage.

Completed in 1970, the Copacabana promenade features an iconic undulating mosaic pattern that reinterprets the traditional design of Lisbon’s Rossio Square. Stretching 2.5 kilometers, this mosaic is one of the largest in the world, with its black and white tiles enhancing the coastal view and framing the iconic Sugarloaf Mountain.

By elongating the curves and aligning them with the sea, Burle Marx created a harmonious connection between the natural landscape and Brazil’s colonial history. He ensured that the connection remains a central part of urban life and that it embodies the city’s character and enhances its resilience to environmental challenges.

Similarly, the Pedregulho project demonstrates Burle Marx’s strategic use of landscape design to enhance residential spaces. By incorporating native plants and thoughtful layouts, the landscape architect created multifunctional outdoor areas that provide natural cooling, privacy, and community interaction zones.

This approach — commonly developed by the landscape architect in residential projects — aligns with the architectural vision while addressing residents’ needs. It demonstrates how landscape elements can be integral to the overall project.

In these projects, Burle Marx’s design philosophy emphasizes creating visually appealing yet adaptable spaces, setting a standard for resilient urban landscapes that serve immediate and future community needs.

Throughout his work, Burle Marx viewed plants not just as botanical specimens, but as elements of color, shape, and volume in his artistic compositions.

“A garden is a complex of aesthetic and plastic intentions; and the plant is, to a landscape artist, not only a plant — rare, unusual, ordinary, or doomed to disappearance — but it is also a color, a shape, a volume, or an arabesque in itself.”

His lessons are more relevant than ever as we confront the twin crises of climate change and biodiversity loss. His legacy encourages a holistic approach to urban design, emphasizing the integration of cities with larger ecosystems. By adopting his principles, contemporary landscape architects and urban planners can create sustainable, vibrant, and life-affirming environments that benefit both people and ecosystems.

Diogo Borges Ferreira is an architect, researcher, and editor based in Porto, Portugal.

This article was originally published on ArchDaily and is part of a collaborative series on landscape architecture and climate and biodiversity solutions. See more of their related coverage.