A few months ago some stories were circulating about how Florida should ditch palm trees to fight the climate crisis. While it’s an attention-grabbing headline, there is far more nuance that needs to be added to the conversation.
“There are lots of other things that trees do besides just sequester carbon,” says Jason Henning, a research urban forester for the Davey Institute. “One of the things that we study is how trees can shade buildings, which reduces energy use and if you reduce energy use, you’re burning less fossil fuel so you’re saving carbon in another way. There are other considerations that can add nuance to that discussion.”
One of the points made is that palm trees are ineffective at sequestering carbon, but Scott Maco, director of research and development for the Davey Institute, argues palm trees aren’t necessarily ineffective, they just can’t sequester carbon at the same rate as other trees.
“The reason for that is palms are something I don’t even think we would technically call trees,” Maco says. “They’re more related to grasses than anything. They have a different structure to their biomass, with a kind of pulpy fibrous woody structure. It’s just not as dense as it is for either a true softwood or a hardwood tree.”
Henning adds that a palm tree is going to be better at sequestering carbon than grass in the same space because it has more biomass. Similarly, an oak will be better at sequestering carbon than a palm tree because it has more wood and leaf surface area. Trees that have a more extensive root system, larger trunk and branches and a broad canopy have more biomass to store carbon.
“You’re just going to get more out of that tree that has more structure to it, that has branches, and has a wider crown,” Henning says.
So since this is true, shouldn’t Florida go about replacing palms with other native trees as soon as possible? Not quite.
“A palm might be less effective at carbon sequestration than a live oak, but nonetheless, it is sequestering carbon,” Maco says. “It’s a good, hearty, well-adapted, long-lived tree, probably 70 to 100 years. They can live without much trouble. So, I wouldn’t cut them down, but if you had the opportunity to replace them because they’re sick, dying or got destroyed in a windstorm, you could think about if there is there an opportunity to plant more effective trees based on the local environmental priorities.”
Henning says that you wouldn’t catch up from a carbon standpoint if you went tree by tree and replaced healthy mature palms with a new small tree, because some of these replacement trees will die.
“If you were to cut them down and replace them, there’s going to be a gap in time where you’ve lost some carbon sequestration ability that you could have otherwise had with that palm until that new tree catches up and potentially overcomes, but that could be 10, 20, 30 years down the road,” Maco says.
Maco adds that palm trees are iconic for locations like Florida and provide a sense of place.
“The South Florida landscape is a special place that supports a greater diversity of palm species than anywhere else in the Eastern United States,” says Matt Borden, plant pathologist with Bartlett Tree Experts. “Palms are, and will always be, an iconic part of the canopy and prized aesthetic of the region. Reevaluating how and where palms are best used has every potential to enhance, rather than reduce, the role of palms. Positive steps include diversifying the species of palms in use for greater aesthetic interest, increasing benefits to wildlife, clustering palms for safety and storm tolerance, and reducing the impact of serious pest and disease concerns.”
In the end, it comes down to planting the right tree in the right space.
“There are other considerations; it’s where you plant that tree,” Maco says. “If you plant a big stature live oak, over a 25-year period, that live oak could sequester almost 14,000 pounds of carbon. That’s substantial. If you put that on the west side of a residential property, the shade value, the offset in energy use, the offset of fossil fuels that go into producing that energy, you’ll get an additional 7,000 pounds of carbon savings for a total of almost 21,000 pounds. So, you can maximize your benefits for any one tree by strategic placement of that tree.”
In the same location, a cabbage palm would sequester an estimated 461 pounds of carbon over the same 25-year period. You can determine the benefits a tree will provide with this tool.
Ideally, you do want to plant the biggest tree in the space, but there are other considerations that come into play, such as the maintenance and commitment you can provide for that tree.
“The urban landscape is a difficult environment for plants to thrive,” Borden says. “We desire our trees to perform well despite being faced with numerous stress factors reducing their potential. Planning and maintaining a healthy, diverse urban canopy in the face of severe weather events, salt intrusion, poor soils, pollution, and shrinking available space is no small task.”
Borden says while carbon capture comparisons to shade trees have been a helpful and popular discussion topic, it should be recognized that palm replacement at this scale will not significantly mitigate the roughly quarter of a billion metric tons of annual energy-related carbon dioxide emissions produced in Florida alone.
“Rather, we should not let this detract from the full array of clear benefits intended by the proposed diversification of the urban canopy in South Florida,” Borden says. “Planting more shade trees and keeping them healthy will benefit all. Stormwater interception, ozone and particulate removal, water filtration, shade and cooling effects, and wildlife habitat are just some of the valuable services that sometimes go overlooked.”
“There’s still a place for palms, there’s no doubt about it,” Maco says. “Any green in the urban landscape is a good thing.