San Diego is being hit by another record-breaking heat wave over Labor Day weekend. As much as the skyrocketing temperatures are shocking, they are becoming routine in Southern California where the effects of climate change continue to worsen.

Amid efforts to stay cool and fight climate change, the city has a secret weapon: its urban forest. On an individual level, its easy to step under a shaded area and sense how much cooler it feels than being in direct sunlight. Expanded to a community level, a neighborhood with large, shady trees can be up to 20 degrees cooler than a neighborhood without mature trees populating the landscape.

“Trees are known to cool neighborhoods in the summer by reducing the heat island effect through shading and evapotranspiration where trees take up moisture through the soil and release [it] into the air through the leaves of the tree,” explained Brian Widener, City of San Diego Forester.

Many aspects of the built environment can make hot temperatures worse. Pavement, cement and the facades of large buildings can all be absorbant surfaces that heat up faster and trap heat longer than the natural environment. This heat island effect means urban areas can experience hotter temperatures than outlying rural areas.

Although the ocean breeze mitigates this in coastal parts of San Diego, another way to prevent this effect is through trees.

“Trees provide shade, support biodiversity, and help fight climate change by absorbing carbon dioxide. Just as important, trees by way of their lush canopy, help reduce the heat island effect,” said Jimmie Webb, SDG&E’s Utility Forester.

The urban forest is an important aspect of San Diego’s Climate Action Plan since trees capture and store carbon. In the updated CAP, San Diego plans to plant 40,000 new trees by 2030 and 100,000 by 2035 – the deadline for the city reaching zero Green House Gas emissions. According to Widener, every effort is made to maintain the trees already growing on city streets and parks. Large trees have more carbon stored than young saplings so their loss is particularly impactful.

“As we increase the CO2 in our atmosphere that contributes to the increase in temperatures, trees are a great way to pull that carbon out of the atmosphere for long-term [storage] in the branches and trunks,” said Vince Mikulanis, director of Western operations for the Davey Resource Group.

SDG&E has made a similar pledge to plant 10,000 trees annually in its service area. At least 2500 of those trees will be within the city borders over the next decade. One of the reasons SDG&E made this commitment was due to the need to occasionally fell trees that disrupt power lines.

Although removing trees is the last scenario after other options, such as trimming or reshaping the trees to grow around the power lines have failed, the utility found not all customers wanted the company to replace the trees on their property. They took this task on themselves and help empower customers who do want to plant trees through the Community Tree Rebate program and free consultations with arborists.

The city has a similar program, Free Tree SD, where residents can request a street tree to be planted near them as long as they commit to watering the tree for three years.

Despite efforts from arborists to keep trees alive, there are times when a tree has died or needs to be removed. Traditionally, a dead tree in the city would be chopped into firewood, sent to a landfill, or ground into wood chips. All of those methods mean that the carbon stored in the tree’s branches and trunk throughout its lifetime will be released back into the atmosphere when the wood is exposed to oxygen.

This carbon cycle is carbon neutral and a natural process. It would be fine if not for the massive amounts of greenhouse gases humans were already releasing into the atmosphere.

“In a world where we’re taking so much more from the earth than we’re giving back, we need ways in which we could slow down that decomposition, slow down that rerelease of greenhouse gas emissions back to the atmosphere,” said Tom Hamilton, the founder of Lumbercycle.

Lumbercycle is one of a few local organizations working to divert those trees from landfills by using them as urban timber. The ultimate goal is to have a sustainable urban forest. When a dead tree is turned into lumber that is then dried and made into a piece of furniture, the wood decomposes much slower. The tree’s carbon is sequestered inside that furniture rather than being released into the atmosphere.

The urban forest has untold other benefits economically and environmentally. Trees help manage stormwater drainage and filter out pollutants in the air. Dust and detritus are caught by leaves so the air is more clean. Studies have shown people will shop longer if there are shady trees outside a store and trees increase property value. Trees also improve cities’ walkability and mobility. Even pavement lasts longer when it is shaded, thus requiring less maintenance.

“Trees do sort of filter the air that we breathe. And that’s why planting in areas like Barrio Logan, where we’ve got the shipyards and that sort of activity, [is important] for the citizens that live in those areas,” said Mikulanis, who also serves on the San Diego Regional Urban Forests Council.

With the benefits of the urban forest increasingly clear, many entities have embraced tree planting efforts. The County of San Diego passed several initiatives on Wednesday, Aug. 31 as part of regional decarbonization framework, including expanding a tree-planting program.

“We are continuing progress on a new roadmap for regional decarbonization. Today we took actions to accelerate these efforts, including to create an equity-driven tree planting program to reduce heat in urban areas,” Board of Supervisors Chair Nathan Fletcher said. “These are important steps to eliminate carbon emission and protect our environment; and taking these steps will make our region a better place to live for the next generation.”

Arborists and urban forest managers are focusing on ensuring the correct trees are planted for the future.

Some trees that have resided here for centuries are no longer compatible with the area’s hot temperature and drought conditions or will not be in the future as those issues worsen. For instance, the city cut down an entire grove of redwood trees near Balboa Park a few years ago. The native trees were over a hundred years old but could not survive current conditions.

Another tree foresters are moving away from are fan palms. While the palms are part of Southern California’s pop culture mythology, they require frequent maintenance to prevent them from being a fire hazard and do not provide much shade.

SDG&E tree planting programs focus on planting shade and fruit trees that will not interfere with power lines above and below ground.

“Part of my job is to inform the public about planting the right tree in the right place to avoid conflicts with utility infrastructure. Consequently, our vegetation management team monitors and cares for about half a million trees located near our infrastructure,” Webb said.

Lumbercycle is advocating that amid tree planting efforts, thought will be put into the entire life cycle of the tree, including what lumber it could become. One native species Hamilton hopes will be planted more is black acacia whose timber works as a walnut replacement since the popular tree does not grow locally.

For Lumbercycle’s part, San Diego’s Eucalyptus trees are a huge challenge. Since the trees grow in a spiral, it is difficult to dry the lumber evenly and it often cracks. Although supply of dead Eucalyptus outpaces Lumbercycle’s ability to utilize it, the organization has found creative uses for it. Since the wood is very hard, the nonprofit has turned it into planter boxes in community gardens. The density of the wood means it will rot much slower than other timber, such as pine. They have also used it for hundreds of simple benches.

“We can slab eucalyptus logs on a couple of log bases and because we found if you’re just gonna stick your tush on it, it doesn’t really matter if it warps a little bit or cracks a little bit,” Hamilton explained. “It could still be a really nice sit.”

The city of San Diego views the Eucalyptus trees as an important part of the urban forest.

“Eucalyptus trees are some of our largest tree species in the region and contribute significantly to the City’s climate action plan goals for tree canopy cover and the many other benefits that large trees provide to our communities,” said City Forester Widener. “Larger trees provide more benefits to our communities.”

In addition to what trees to plant, there is also a focus on where to plant. Mikulanis noted the need for trees in industrial areas where pollution harms the citizenry. Meanwhile, the city’s tree planting efforts until 2030 will largely focus on “Communities of Concern” that have low rates of opportunity according to the Climate Equity Index.

As part of the effort to equitably disperse trees, the city partnered with SDG&E to plant 400 trees in City Heights. Eventually, those trees will help cool and improve the walkability of the diverse yet poor neighborhood.

The partnership between the city, utilities, and nonprofit organizations will help the urban forest blunt climate change, keep neighborhoods cool, and provide useful lumber into the future.