The issue of climate change and its impact on human health has captured scientists' attention for decades. Recently, experts also try to understand the effects of this phenomenon on trees from various parts of the world. Advances in imaging technology help them explore forests from various parts of the world.
Search for the Cause of Longer Growing Season
It has been observed that urban trees tend to green up earlier and lose their seasonal vegetation leaves later as compared to trees in rural and natural areas. It was previously accepted that the longer growing seasons are largely caused by urban heat. However, a team of researchers led by Prof. Michael Alonzo from American University's College of Arts and Sciences challenged this theory.
Most research studies focus on urbanization and blame urban heat as the cause of a more extended growing season. Alonzo believes that although urban heat has a role in this phenomenon, scientists may be overstating its significance.
The former theory is supported by the data from moderate-resolution satellites producing pixelated images. As a result, a mixture of grasses, plants, and trees in every pixel appears like tree canopies in urban areas where greening up happens early.
Complex and varied vegetation can be observed along the streets of any city, where they mix closely and are interspersed with impervious surfaces. Pixelated images from the type of satellite formerly used by scientists do not allow the individual study of the vegetation nor provide imagery daily.
A Better Approach to Forest Monitoring
Understanding the variety of species composition between rural and urban areas is very important in improving the models intended to show the response of trees and other vegetation types to heat. According to Alonzo, understanding the changes in the life cycle of a plant can be done better by zooming in on individual trees to see how they respond to their environment.
Alonzo and his team used satellite technology to study large areas of trees and their growing seasons. They utilize the potential of CubeSats in forest monitoring. These miniature satellites orbit as small as a shoebox, helping environmental scientists make better measurements about trees' response to global warming. With CubeSat imagery, scientists can monitor changes like the day-to-day development of leaves as soon as the growing season begins.
From the high-resolution images taken by Cubesats, Alonzo and his team conducted new research regarding the role of heat in the advance growing season of urban forests. They monitored over 10,000 tree crowns in Washington, D.C., From 2018 to 2020; they observed the growing seasons of 29 broadleafs and leaf-shedding trees.
After downloading the CubeSat imagery, the team pieced together hundreds of photographs taken almost every day, focusing on when the trees green up in the spring and lose their leaves in the fall. Then they tried to connect the type of tree species and the duration of their growing season. They also considered how other factors like air temperature and impenetrable surface cover could affect the observed timings.
From the result of their study, it was revealed that urban heat is not the culprit for the early onset of the growing season in urban trees. Although the research was done on trees in Washington, D.C., Alonzo is confident that their findings can be applied to other urban and non-urban regions involving various trees.
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