Photo by Lance Asper on Unsplash
When we think of Miami Beach, we think of sun, surf and – of course – palm trees. But according to a recent article published in the Miami Herald, local officials have agreed a long-term plan that will see city undergo a makeover over the next 30 years that will see a significant reduction in the number of palm trees. The plan is motivated by several considerations, most of them linking back to climate change… and unfortunately, palm trees fall short in several key categories.
Shade
A study in Richmond, VA found that while cities, on average, are hotter than the surrounding countryside (due to the heat retaining effects of tarmac, a higher concentration of vehicles and high rise buildings), shadier neighbourhoods can actually be up to 16°F cooler than areas that are more exposed to the sun. During the height of the summer, this is a significant difference indeed.
And even though we may associate palm trees with tropical getaways, but this type of plant does not actually produce a lot of shade. In fact, NOAA scientists observed that despite the prevalence of palm trees in West Palm Springs, the downtown area reached a heat-index temperature of 122°F in August 2019, while the Grassy Waters Preserve nature preserve only reached 92°F.
According to a 2018 revision to the city code, developers need to put more emphasis on shading the urban landscape, especially in high-tarmac areas (such as parking lots), where 75% of the required trees must now be shade trees. Palm trees fall short when it comes to providing adequate shade because they are not actually a tree – they are a grass. This means that their canopy is not as dense, as rigid or as expansive as actual trees, so even though it may look like there are providing shade, they are not able to sufficiently cool their vicinity, as that shade moves around too much.
Air quality
In addition to providing shade and injecting some colour into otherwise monotonous urban landscapes, trees also help improve air quality by sucking greenhouse gases (like carbon dioxide and ozone) out of the air and storing it.
But, once again, palm trees are not the best choice if we want to breath cleaner air in a city. According to the Miami Beach Urban Forestry Master Plan, in comparison to an oak tree of the same size, a palm tree only stores 2.71 pounds of CO2 per year, versus the staggering 510 pounds sequestered by the oak, which leads to a difference of over 3,000 pounds over the trees’ lifetime.
Water management
A third benefit offered by trees is in terms of water management. Trees intercept rainwater and divert it towards their roots, helping replenish groundwater supplies. This is especially important in hot areas (which are only set to get hotter due to the effects of climate change) where drought is becoming a growing issue.
According to the Miami Beach Urban Forestry Master Plan, in comparison to a palm tree (which intercepts just 81 gallons of rainwater per year), shade trees are much better at minimising the effects of tropical showers, such as flooding. For instance, a Royal Poinciana will divert 2,211 gallons of rainwater from the sewers and stormwater management systems each year, while an oak tree will divert 3,394 gallons.
While not everyone is happy with the proposed change, officials have clarified that they will not be taking a chainsaw to the city’s palm tree population. Instead, the city will opt for alternatives when planting new trees, especially around the suburbs to make living and walking in the city more pleasant during the warm summer months.