The Benefits of Trees

The following is an excerpt from People, Planet, Design: A Practical Guide to Realizing Architecture’s Potential published by Island Press.

Trees are the answer to so many of civilization’s challenges. They stabilize the earth, manage stormwater, and provide habitat for animals and protection from the sun. Trees cool their surroundings in the summer through evapotranspiration to mitigate the heat island effect, and they keep their environments warmer in the winter by insulating from night sky radiation. In addition, trees pull carbon from the atmosphere and clean the air, water, and soil in their midst, all with a material makeup that’s endlessly recyclable. While providing these useful functions, the tree is quietly creating wood, an economically essential product whose benefits are described throughout these chapters. Perhaps most important is the oxygen that supports the lives of breathing organisms, which trees release not as a gift but as a byproduct of their own metabolic activity. For all their practical and useful functions, trees would be forgiven if they were unattractive or noisy or otherwise inconvenient, the same way we give building construction a pass on these fronts because we consider the outcome worthy of the disruption. But this is not the case with trees. In addition to all the economically valuable services they provide, they are beautiful as pure aesthetic objects and a welcome presence in any landscape.

Considering all that they contribute and their lack of drawbacks, trees can also serve as a model for what architecture should be working toward achieving. If the built environment could mimic trees by flawlessly serving their useful function while contributing to the greater good, so many challenges could be addressed all at once. We’re accustomed to thinking that solving one problem will require a trade-off somewhere else. We can use a car to get to a destination faster but only with the costs of gas, noise, pollution, and wasteful urban planning. Likewise, we can construct a building to serve a need in one location, but the extraction and manufacture of construction materials might cause problems elsewhere. Even a simple action of turning on the lights to see in the dark will probably result in air pollution and carbon emissions. Traditional practice embodies the idea that making an omelet requires breaking a few eggs, but informing a tree of the need for trade-offs would be met with laughter. Of course, it’s possible to individually thrive without causing damage to others. This is what every one of the earth’s three trillion trees does every day. What if architecture could do the same? A building that improves the world rather than just causing less damage is as challenging as it is desirable. It’s also the way to address many big problems, from climate, to ecology, to equity, in the built environment all at once. While the challenges are real and just deciding to design a building that acts as a tree will not on its own make it happen, the analogy of the tree can remind designers not to settle. There are design solutions that can effectively achieve their objectives with minimal or even positive impact. Simple examples include daylighting, bicycle transportation, and thoughtful material selection that supports a local economy. Every project can begin by striving to be a tree, and eventually the industry might get there.

Beyond the metaphor of how a regenerative building could function, trees are really useful and can enhance many aspects of the built environment. From shading to offering interesting views, having more trees onsite is almost always better. A view through a window means little if the sight lines lead to a parking lot or blank wall. At the most basic level, trees provide the visual interest and the biophilic qualities that have been shown to reduce stress, increase concentration, and comfort the psyche. Even if the building itself does not act like a tree in the way it leverages resources, the trees nearby can contribute to the overall functionality of the site when the building and adjacent landscaping are evaluated as a single system. Too often, trees are not given the deference they deserve, and on many sites, trees are unnecessarily razed to make buildings easier to design and construct. A better option is to treat trees as valuable resources and to design in a way that leverages their benefits. It might not be possible to save every tree on a given site, and trees exist along a range of qualities, with, for example, a large oak being more valuable than a young cedar, but architects can still elevate the importance of existing trees during site design and building massing. Designing a building to fit between or around existing trees will pose challenges, but the outcomes can be worthwhile, especially if trees are mature or larger than newly planted site trees might be. Consider how these trees can provide shade or visual interest and work with them rather than just around them.

Carbon sequestration

Adding new trees to the site is also a valuable endeavor, and the location and quantity of new trees can be considered from the beginning of the design process. A site with a greater postconstruction herbaceous biomass than what was found before development is a useful design goal. Plants, shrubs, and especially trees sequester some of the carbon that will be released during construction. While a building can run off of 100 percent clean energy and thus achieve net-zero carbon operations, the only way to be fully carbon neutral is to offset the carbon embodied in construction materials. The most common strategy for this is to purchase carbon offsets, which, in the best cases, will fund carbon reduction projects around the globe. These projects can include investments in clean energy infrastructure, land conservation, landfill methane capture, or, yes, tree planting. While they are potentially beneficial, there are real limits to the utility of carbon offsets since it is uncertain how effective many of these investments will end up being in the long run. Sequestering carbon onsite is another option. A single tree, depending on the species, climate, and other factors, can sequester around a tonne of carbon dioxide over its lifetime. Compared with the typical embodied carbon of a single-family home, about 50 to 100 tonnes, the impact of a tree seems small. However, if efforts are made to keep construction on the lower end of the carbon spectrum and the site is designed to support ten trees, then about 20 percent of the carbon released during construction of the home will be resequestered over the building’s useful life. Larger buildings pose an issue of scale, with many hundreds or thousands of trees needed to offset the embodied carbon of commercial buildings. While space for site trees is difficult to secure in urban areas, elsewhere, significant acreage is turned over to parking lots without a second thought about the land’s highest and best use. An acre of parking can provide space for 242 cars or, if that land use were prioritized differently, 100 mature trees, which could go on to sequester 100 tonnes of carbon dioxide. While only rural areas can realistically offset building embodied carbon entirely through site trees, maintaining as many trees as possible will make a dent in addressing embodied carbon and result in a more humane and enjoyable environment.

Natural cooling

Beyond carbon, trees provide many immediately tangible benefits to building users, many of which would require significant financial investment to achieve the same outcome that trees provide for free. Mitigating the urban heat island effect is an example of how trees can improve the lives of those living among them. In urban areas with excessive hardscape, unshaded concrete and asphalt absorb the sun’s heat and increase the temperature of the surrounding area. The impact can be dramatic, with summer temperatures differing by more than 10 degrees between neighborhoods that are just a mile or two apart. Often, it’s the historically wealthy neighborhoods that have ample tree coverage and more moderate microclimates compared to the underserved areas, which are more likely to be barren and hot. Significant energy and operating costs, not to mention system capacity, would be needed for air conditioning to manage an additional 10 or 15 degrees, making scarcely planted neighborhoods both inherently less comfortable and more expensive to achieve thermal comfort within buildings. In many places that are only beginning to experience extreme heat for the first time, those with neither air conditioners nor the moderating effect of trees can be subject to especially dangerous conditions. One of the easiest and least expensive ways of addressing extreme heat is by planting more trees in urban areas. Shading from trees will keep the sun off of the surfaces that would otherwise absorb its heat, and evapotranspiration will keep the air cooler. While more air conditioning will be necessary to keep building occupants safe and healthy in a world with increasing summer high temperatures, trees and active cooling systems can work hand in hand, adding resilience and minimizing the financial investment needed to keep buildings comfortable.

Stormwater management

As temperatures increase, we can expect the intensity of storms to increase as well. A changing climate will lead to some places getting wetter while other areas dry out, but in both cases, individual storm events will result in more water falling over shorter periods of time. This increase in sheer quantity of water can quickly overrun municipal stormwater systems, which were designed based on historic rainfall data, and they are unlikely to be prepared for what will come in the future. Again, trees can be the answer. Trees absorb water from the ground into their structure, where it can be evaporated through the leaves. A single live oak tree can move 40,000 gallons of water a year from ground into the air through evaporation. This effect can have a large impact on urban stormwater management. A city with an additional tree per property would have millions of fewer gallons of water to deal with during major storms. Managing this additional stormwater through other means would require significant investment in urban infrastructure, not to mention the additional carbon emissions associated with building concrete channels or detention vaults. The more trees, the cooler the site, the more resilient the building, and the less stormwater the municipal system will need to manage. The alternative is expensive systems that don’t look nearly as good or work nearly as well. Investing in trees will allow resources to be freed up for investment in education, culture, social services, or any number of other priorities.

Food production

Food production is another advantage that can be attributed to trees but not to air conditioners or concrete culverts. Trees have the potential to produce a lot of food, and when they are planted in proximity to buildings, that food is produced close to the people who will enjoy it. A single apple tree can produce over 500 pounds of fruit per year, and a walnut tree can produce over 50 pounds of high-protein nuts. Trees can also provide culinary herbs and spices, such as bay leaves, or sap that can be boiled down into syrup. Harvesting from dispersed fruit trees poses a challenge of inefficiency, and plenty of fruit and nuts that are grown in urban areas will end up going uneaten. There is still potential, even on a smaller scale, to offset some of the industrially produced foods that would otherwise be shipped to population centers and sold in supermarkets or for organizations to connect disparate sites of production with people in need. Food-producing trees offer a degree of resilience and the special joy of eating produce directly from the source or foraging on a neighborhood walk. Onsite food production can connect us to the uniqueness of a given place just as effectively as the best interpretation of regional design. The seasons come into focus as different foods become available throughout the year. A similar connection to place can be achieved by bringing trees inside buildings, both as indoor plants and as wood finishes.

Indoors and outdoors

Many of the benefits of building with wood are outlined elsewhere, but it’s worth considering the totality of what trees can offer architecture. Trees can inspire, provide practical functions that enhance building performance, and serve as a primary construction material. Wood, plants, or even trees can also be brought inside a building to provide a more direct connection and enhance biophilic benefits. Live greenery and wood finishes evoke comfort and peace of mind in a way that is difficult to replicate in concrete or gypsum. Their presence can also serve as a reminder of the interconnection of all living things. We’re not so different from birds that build nests or beavers that construct dams. Wood can be used to celebrate life, nature, and humanity purely through the innate evolutionary connection that people have to this building material. Bringing plants indoors can serve a similar purpose. The sight, smell, and air purification potential of living plants would be difficult to overstate. When architects talk about blurring the lines between indoors and outdoors, bringing literal nature into a space is more effective than merely seeing the natural world through glass. However, there are some situations where trees are better left where they are and not transformed into products. This is the case with tropical hardwood. Species such as ipê, cumaru, and mahogany are sought after for their properties of strength, durability, and rot resistance, especially for use outdoors. The danger of building with tropical species, despite their beauty and beneficial qualities, is that their extraction will probably contribute to deforestation of one of the most important ecosystems on the planet. A connection to nature and respect for the natural world are both essential outcomes of architecture. As the world faces a crisis of atmospheric carbon, the last thing we need is a diminished tropical rainforest, which could otherwise be sequestering that carbon back into its biomass. Connect people with living nature when possible, and when using wood, stick with Forest Stewardship Council certified domestic trees, which, depending on the species or preparation, can be just as durable but make it far easier to ensure responsible and forward-looking forestry practices.

Simply more trees

Living, working, and playing among trees is as nurturing to people as it is to the animals that call urban trees home. Native tree species will support habitat for birds, insects, and small mammals that bring an additional degree of life to the built environment. Environments that support plant and animal life are more interesting places to inhabit.

This is even the case in subtle ways, such as watching squirrels through a window or listening to crickets chirp at night. A more thorough integration between trees, buildings, and urban planning can blur the overly rigid line between the human and natural worlds, fostering a deeper relationship between people and the planet and resulting in human environments that are more humane, healthy, functional, and fun. While much time and effort are dedicated to the technology that will allow humans to live in harmony with the planet, a large part of that solution simply involves more trees.

Corey Squire is an architect and nationally recognized expert in sustainable design who has empowered multiple award-winning design firms to achieve high-performance projects across their portfolios. He lectures nationally on a range of sustainable design related topics and was a lead author of the AIA Framework for Design Excellence, a resource that’s actively redefining excellence in the built environment. Squire is an Associate Principal and Director of Sustainability at Bora Architecture and Interiors in Portland Oregon, where he lives with his Family.  He is the author of People, Planet, Design: A Practical Guide to Realizing Architecture’s Potential published by Island Press.