When I was younger, I remember thinking to myself: “This tree is losing its skin, is it dying?” I believe I can’t be the only child that thought this when first looking at a London plane. Little did I (and the other children) know, this was one of the London planes’ amazing abilities that made it able to thrive in city environments. When we realized the amazing properties of the London plane, we started planting them across European cities and even the United States and Australia. Using its properties to our benefit, the London plane solidified its place in the urban green space. However, recently the London plane seems to be falling from favor. But what exactly happened to the London plane that began its fall from grace?
Natural urban predisposition
The London plane (Platanus x hispanica) is a large deciduous tree that generally grows up to 40m tall and has a very large canopy. Originating in the 17th century, the London plane is a natural hybrid between the oriental plane (Platanus orientalis) and the American sycamore (Platanus occidentalis). Because the London plane is such a large tree, it is perfect to use for the shade it provides. Not only does its large canopy provide protection from the sun, it also provides a way to combat the effect of the urban heat island (Ettinger et al., 2024). Another property of the London plane, as alluded to earlier, is its ability to exfoliate (or shed) its bark. Periodically during spring and summer, the London plane will exfoliate small patches of its bark, creating the spotted pattern that these trees are well known for. The shedding of the bark helps protect the trees by increasing its resilience to urban pollutants, infestations and severe droughts (Esper et al., 2023). Together with its resistance to frost and moderate wind (Cariñanos et al., 2020), the London plane was a much sought after form of vegetation for urban green spaces, providing it with the perfect opportunity to take over western cities.
Trouble in the air
Very useful and incredibly tolerant: It seems the London plane has everything going for it, so what is happening to our preference for this wonderful tree? The first issue ties back to its immense canopy. A large canopy not only comes with the benefit of shade, but it also leaves behind a large amount of organic debris during its annual foliage renewal. The bigger issue, however, is the effect that allergens and pollen emitted by the tree have on the human population. The London plane tree has a very effective wind-pollination strategy. It produces around 3.3×106 pollen grains per infloresence (a group of flowers or clusters of flowers arranged on a stem), which is one of the highest of the woody wind-pollinator species (Cariñanos et al., 2020). Although the exact number is not known, reports of symptomatic responses can start as soon as pollen concentration reaches 50 grains/m3 (Alcázar et al., 2004). This means that people with pollen allergies will experience symptoms very quickly.
But if the pollen is such an issue, then why have we only recently started to shift our perspective of the London plane? The simple answer: climate change. As a result of rising CO2 concentrations and temperatures, there have been changes in the intensity of the flowering and the amount of pollen emitted (Cariñanos et al., 2020). Add to this the effect of air pollutants modifying the allergen content of the pollen and the London plane is slowly turning into enemy number one.
Conclusion
Granting us benefits and resisting the immense pressure we put on organisms in our urban environments, the London plane has shown itself to be a reliable ally. With its distinct features and looks, it has defined out cities’ green space over the past decades. However, with climate change intensifying every year, it seems the London plane is losing our favor. Irony dictates that increases in air pollutants and temperature, which the London plane is able to tackle so well, are turning out to be its downfall. Losing a tree with so much character would be a loss for any green space. And although I realize they won’t be gone any time soon, I believe we should appreciate them even more in the years to come before they are gone from our parks and streets.
References
Cariñanos, P., Ruiz-Peñuela, S., Valle, A. M., & De La Guardia, C. D. (2020). Assessing pollination disservices of urban street-trees: The case of London-plane tree (Platanus x hispanica Mill. ex Münchh). The Science of the Total Environment, 737, 139722. https://doi.org/10.1016/j.scitotenv.2020.139722
Esper, J., Cherubini, P., Kaltenbach, D., & Büntgen, U. (2023). London Plane bark exfoliation and Tree-Ring growth in urban environments. Arboriculture & Urban Forestry, jauf.2023.021. https://doi.org/10.48044/jauf.2023.021
Ettinger, A. K., Bratman, G. N., Carey, M., Hebert, R., Hill, O., Kett, H., Levin, P., Murphy-Williams, M., & Wyse, L. (2024). Street trees provide an opportunity to mitigate urban heat and reduce risk of high heat exposure. Scientific Reports, 14(1). https://doi.org/10.1038/s41598-024-51921-y
Alcázar, P., Carinanos, P., De Castro, C., & Galán, C. (2004). Airborne plane-tree (Platanus hispanica) pollen distribution in the city of Córdoba, South-western Spain,. . . ResearchGate. https://www.researchgate.net/publication/8174023_Airborne_plane-tree_Platanus_hispanica_pollen_distribution_in_the_city_of_Cordoba_South-western_Spain_and_possible_implications_on_pollen_allergy
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