Reasons to Save Existing Big Trees in Urban Areas

Saving big trees in urban areas is difficult, particularly during development as cities grow in size.. But there are many reasons why saving big trees and planting new trees that will become big over time is important. Excerpts from 3 separate articles  below help to explain why.
Note – The bolding of the text below is mine to help focus on the issue of the value of big trees, not that of the original authors.
1. The Large Tree Argument – the Case for Large-Statue Trees vs Small-Stature Trees , Center for Urban Forest Research, Southern Center for Urban Forestry Research & Information 2004
Large trees pay us back. We now know that, dollar for dollar, large-stature trees … deliver big savings and other benefits we can’t ignore. Small-stature trees like crape myrtle deliver far fewer benefits. In fact, research at The Center for Urban Forest Research shows that their benefits are up to eight times less. Compared to a small-stature tree, a strategically located large-stature tree has a bigger impact on conserving energy, mitigating an urban heat island, and cooling a parking lot. They do more to reduce stormwater run off; extend the life of streets; improve local air, soil and water quality; reduce atmospheric carbon dioxide; provide wildlife habitat; increase property values; enhance the attractiveness of a community; and promote human health and well being.
And when we use large stature trees, the bottom-line benefits are multipliedWhen it comes to trees, size really does matter. Don’t forget the established “Old Guard” We can’t forget the already-established trees. These older trees provide immediate benefits. The investment that community leaders made 30, 40, 50 years ago is producing dividends today. Dr. McPherson, Director of the Center for Urban Forest Research, points out that “since up-front costs to establish these large-stature trees have already been made, keeping these trees healthy and functional is one of the best investments communities can make.”” 
     
2.  The Struggle to Save Seattle’s Urban Forest in the Face of Development, Seattle Magazine, October 2017, University of Washington social scientist Kathleen Wolf, Ph.D
“Wolf knows this research well, because her own work is focused on how people experience nature in cities, including the human health and economic benefits of the urban forest—the phrase used to describe the trees and understory plants in a city. Forest bathing aside, research shows our health is boosted by having access to urban trees and other nature. “Neighborhood greening reduces depression, may help kids reduce ADHD symptoms, reduces our stress response, encourages physical activity, reduces signs of mental distress, increases cognitive memory, improves air quality and, overall, promotes significantly higher well-being,” she says.

City trees can also raise property values, reduce crime and muffle urban noise. They help the environment, absorbing water, decreasing flooding and the need for water treatment, and absorbing and storing carbon dioxide, directly fighting climate change. “Up until recently, trees really didn’t have a place at the table with city decision making, but now, because we know about their environmental services and the health benefits, trees are an important component of city decision making,” says Wolf. ” ….

Wolf says large trees provide “a much greater proportion of benefit” to cities compared to small trees, in terms of ecosystem services, such as water quality, air quality and carbon sequestration. “Are we going to relegate large trees only to parks and green spaces, or can we incorporate them into development?” she asks. “I’m not sure.”

3.  When it comes to the Climate, Older trees do it Better, Bryan Walsh, Time.com, Jan.15, 2014

“…according to a new study published in Nature, it turns out that the oldest trees are actually still growing rapidly, and storing increasing amounts of carbon as they age. An international research group led by Nate Stephenson of the U.S. Geological Survey Western Ecological Research Center reviewed records from forest studies on six continents, involving 673,046 individual trees and more than 400 species, going back as far as 80 years ago. For 97% of the species surveyed, the mass growth rate—literally, the amount of tree in the tree—kept increasing even as the individual tree got older and taller. Even though trees tended to lose leaf density as they aged…the total amount of leaf cover kept increasing as the tree itself got bigger and older. In other words, the number of leaves per cubic foot fell off but the leafy surface area grew and grew. That enabled the tree to keep absorbing an increasing amount of carbon as it aged.For some species of trees, that increase could be enormous. A single big tree could sequester the same amount of new carbon in a year as might be contained in an entire mid-sized tree.”


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