We know that trees are good — but just how good?
To answer that question, signs have been added to eight leafy giants around Mellon Park in Pittsburgh that quantify the benefits of specific species. It’s part of an initiative between the City of Pittsburgh Forestry Department, Friends of Mellon Park, and Tree Pittsburgh to give visitors a better understanding of how trees improve our daily lives.
Mellon Park made local history in 2021 by becoming Pittsburgh’s first public arboretum. The eight trees are the newest additions to the arboretum. One requirement for arboretum certification is to tag every tree with its Latin and common names. Cathy Droz, with Friends of Mellon Park, said that park officials added some facts about the trees’ benefits in the hopes of cultivating a deeper sense of appreciation among visitors.
“When people have even just a little more knowledge about the trees, they are more likely to be more willing to care about them,” Droz said.
Trees improve our lives in myriad ways, from tangible benefits like improving air quality and cooling homes, to intangible benefits like reducing stress and enhancing cognition.
Take the European Hornbeam for example, one of the more than 100 different species found in Mellon Park. A single Hornbeam has provided $121 worth of benefits over ten years, according to a vinyl sign strung around its trunk. (The temporary sign will soon be replaced with a more permanent tag bearing the same information, Droz said.) A deciduous tree in the birch family, found along a path leading south from Fifth Avenue, the Hornbeam has removed 407 pounds of carbon dioxide from of the air. It also has absorbed pollutants like sulfur dioxide and particulate matter, which, considering its proximity to the heavily trafficked avenue, makes it an invaluable resource for cleaner air.
Finally, this single European Hornbeam has avoided 3,273 gallons of stormwater runoff in the last decade. Stormwater diversion is of particular importance in urban areas, which can overwhelm sewer systems during intense rainstorms. In the Delaware River Basin, PEC encourages the use of Green Stormwater Infrastructure (GSI), such trees along city streets, to filter and absorb stormwater where it falls, reducing the amount of water entering storm sewers.
Other signs offer fun facts about the park’s trees. A gingko, for example, identifiable by its fan-shaped leaves, is one of the oldest species on earth. The oldest gingko fossil dates back 200 million years.
Growing trees in urban spaces can prove difficult. Compacted, nutrient-poor soils, salt damage from winter, pest and disease issues, and the effects of climate change all contribute to a lack of adequate growing spaces. Despite these challenges, groups like Tree Pittsburgh make it their mission to improve biodiversity through their planting efforts.
“In order to have a healthy future urban canopy, we strive for age and species diversity to achieve the many benefits and environmental services that trees provide,” said Joe Stavish, manager of community education with Tree Pittsburgh.
When site conditions allow, his organization prioritizes native heritage trees. Trees with large canopies are especially advantageous. Other factors that go into which trees to plant are seasonal appearances, like spring flowers, leaf shapes, fall color, and winter interests, such as evergreens.
Pittsburgh Parks Conservancy (PPC), which restores and maintains many city parks through an official public interest partnership agreement, understands that a mixture of trees in the same soil layers lead to a healthier, more resilient ecosystem.
“The more diversity of tree species planted, the better chance the trees can cope with environmental stresses,” explained Jaci Bruschi, horticultural manager for the PPC.
“In our restoration areas we plant both canopy, understory trees, and even shrub layers, as many shrubs can growing over 15 feet and provide many ecological benefits,” Bruschi said.
In the natural world, trees supply habitat and food, and fallen leaves provide nutrients for future growth. Roots stabilize riverbanks, and leaves shade the water, keeping it cool.
“Cold water holds higher levels of oxygen than warm water. This is essential for the aquatic life to thrive,” Bruschi explained.
To bring the benefits of trees home, consider planting native species in your yard. The Arbor Day Foundation an online guide, the Tree Wizard, to help you choose the right fit for your specific desires and site conditions.
Pittsburgh also has a new program called the Remarkable Trees of Pittsburgh. Residents can nominate great trees in public spaces, and Pittsburgh Shade Tree Commission selects the winners. Mellon Park is home to three trees from the inaugural list: a bald cypress, a Katsura, and a lacebark pine. You can view a full list of this year’s remarkable trees here.
Exploring these trees presents an opportunity for “forest bathing,” a practice that originated in Japan and that studies suggest offers immense health benefits. Forest bathing involves walking slowly through a forest and focusing on the senses, a kind of ambulatory photosynthesis. Doing so can reduce stress, anxiety, depression, and anger; strengthen the immune system; improve cardiovascular and metabolic health; and boost overall well-being, according to Dr. Qing Li, author of Forest Bathing: How Trees Can Help You Find Health and Happiness.
Scientists are still trying to explain the advantages of forest bathing, but two factors seem to be at play. First, forests contain more oxygen than urban settings, as well as plant chemicals called phytoncides that are part of trees’ immune systems. Exposure to of these, Li writes, provides measurable benefits.
Forest bathing is simple: find a spot in a green area, take a deep breath, and appreciate your leafy companions.