Washington D.C.’s cherry blossoms blooming earlier this year sparked intrigue among researchers. Could it be a sign of trees responding to climate change?
Advancements in imaging technology are aiding scientists in their quest to understand how climate impacts trees. By utilizing high-resolution images captured by cubesats, which are small satellites deployed in low-Earth orbit, environmental scientists can gather more precise data about how trees are responding to a warming climate.
In a recent study published in the journal Science of The Total Environment, Prof. Michael Alonzo, an assistant professor of environmental science at American University’s College of Arts and Sciences, presents new research that challenges the conventional understanding of urban forest growing seasons influenced by heat.
Previous studies relied on pixelated images from satellites with moderate resolution, leading to the belief that tree canopies in cities were greening up earlier due to the heat island effect. However, Alonzo’s analysis of cubesat imagery suggests that urban heat may not advance seasonal vegetation leaf emergence as significantly as previously thought.
“To truly understand whether a particular species or plant is altering its life cycle due to warming, we need to zoom in on individuals and their interactions with the environment,” explains Alonzo.
Investigating the urban heat island effect not only provides insight into how vegetation responds to heat in cities but also offers a preview of how global warming might affect vegetation in non-urban areas. Urban heat islands occur when heat becomes trapped and radiates from surfaces such as pavement, causing cities to be 2 to 3 degrees warmer than surrounding non-urban areas.
Through satellite technology, scientists have observed that trees in cities tend to green up earlier and retain their leaves for longer compared to trees in rural and natural areas. This extended growing season has largely been attributed to heat. However, Alonzo’s work with cubesat imagery challenges this assumption.
“Much of the research has focused on the urban heat island effect as the driving factor behind longer growing seasons,” says Alonzo. “While urban heat does play a role, we may be overestimating its significance.”
Pixelated images from traditional satellites fail to capture the complex and diverse vegetation found in cities, consisting of cultivated trees, shrubs, turfgrass, and natural vegetation interspersed with impervious surfaces. Furthermore, these images are not collected on a daily basis, limiting their usefulness. In contrast, cubesat imagery allows for continuous monitoring of daily changes in leaf development during the growing season.
In his study, Alonzo and his colleagues analyzed cubesat imagery spanning three years (2018-2020) and covering over 10,000 tree crowns in the streets of Washington, D.C. They tracked the timing of green up in the spring and leaf loss in the fall for each individual tree, investigating the influence of species, planting location, air temperature, and impervious surface cover on these timings.
The findings emphasize the importance of understanding species composition variations between urban and rural areas in order to improve models predicting how trees and vegetation respond to heat. Although the study focused on D.C.’s trees, Alonzo believes that the results are applicable to other urban and non-urban regions and various tree species.
Alonzo is part of a pioneering group of scientists who utilize cubesat imagery to study trees, alongside other tools such as drones and traditional satellites. This multidimensional approach allows for comprehensive mapping and monitoring of ecosystems.
In future projects, Alonzo plans to collaborate with professors from the School of International Service to monitor agricultural activity changes in Nigeria and forest transformations in Haiti using cubesat imagery.
More information:
Michael Alonzo et al, Canopy composition drives variability in urban growing season length more than the heat island effect, Science of The Total Environment (2023). DOI: 10.1016/j.scitotenv.2023.163818
Citation:
‘Shoebox’ satellites help scientists understand trees and global warming (2023, June 21).
Retrieved 21 June 2023 from https://phys.org/news/2023-06-shoebox-satellites-scientists-trees-global.html
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