Urban Trees, Human Impact on Nature

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On Wednesday, April 4, Richard Olsen, a Research Geneticist from the National Arboretum, visited St. Mary’s to present his lecture called “The Urban Forest.” Olsen discussed the evolution of trees over the years in urban, rural, and suburban areas. This Natural Science and Mathematics (NS&M) Colloquium was co-sponsored by the St. Mary’s Arboretum Association.

“I’m trying to make this more of a philosophical, fun talk today,” began Olsen. His presentation consisted entirely of photographs as he spoke freely about them. He started off his lecture by talking about root systems of trees and how they work.

“After a storm, we see trees fall over, and we see a pancake of a root system,” he said about the structure of roots. Ninety percent of the root system of a tree is in the top 18 inches of the soil. He showed pictures of effective and ineffective ways of planting trees, and how ineffective ways can lead to girdling roots, which can ultimately kill a tree.

“We’re setting up our urban forest for disaster,” said Olsen as he showed pictures of trees planted directly below power lines. Their top branches will eventually have to be trimmed or cut off, which is not good for the tree.

Olsen explained that the 400 year old dogma of planting urban trees in symmetrical lines along the side of a road needs to be abandoned. Trees need more space to grow.

“We weren’t planting trees in cities until the 1600s,” said Olsen. This is because at that point in time, cities were smaller and usually surrounded by trees, so there was no reason to plant more of them in the city. Poplar trees were the first type of popular street trees in the United States. They symmetrically lined the original Pennsylvania Avenue in Washington, D.C.

Just like expecting them to be symmetrical in layout, building planners also expect trees to look the same. “If you grow things from seeds, you have all sort of different growth rates,” said Olsen. However, if clones are used, every tree grown from a clone will look exactly the same.

Olsen emphasized that planters need to be careful about where they plant trees and with what they surround the trees. Some trees grow best in a dry, arid area, while others are best in wet, swampy areas. For example, the weeping willow is healthiest when grown in a swampy area. Some trees grow steadily over time, while others spend years building up a root system and then suddenly shoot up out of the ground.

Human action widely determines the encouragement or elimination of a species, and humans have the power to lead to the extinction of a particular species of tree. “If you don’t think we’re not affecting pretty much the entire planet, just look at us at night,” said Olsen, showing the audience a nighttime satellite photograph of the Earth.

“Just the presence of all this concrete and asphalt… is affecting the climate,” said Olsen as he discussed how urban land cover can impact seasonal change.

“If you give trees the right space, they’ll grow for maybe 150 years,” concluded Olsen.

“I thought he was funny and was a great speaker, and he started off great with a focused topic on the impact we have on nature,” said senior Don Rees. “He progressed in a sensible way to trees in cities but then at the end just rattled off pictures and examples of trees in cities. He seemed excited but there was no deep analysis or discussion at this point, just a picture show. Overall, not bad but the ending needed work.”

“I agree with Don, it wasn’t the most organized colloquium I’ve seen,” said senior Julie Frank. “Though I really appreciated how excited and passionate he was about his work. Every picture he showed seemed to have a story behind it and a personal connection.”

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