Throwing Shade – How Trees Help Lower Temperatures In Urban Areas
Trees add value to houses and provide beauty for humans to look at. However, trees are more than just attractive. Research in recent years has identified many benefits of trees in urban areas.
Functions Of Urban Trees
In addition to increasing home values by up to 15%, urban trees make cities more livable.
Trees can reduce the urban heat island by providing shade. A tree-lined street is 20-30 degrees cooler than one without trees. In addition, trees lose water vapor from the pores on their leaves or needles to humidify the air.
Trees filter the air. In addition to producing oxygen, trees absorb volatile pollutants. Their leaves and trunk filter small particles out of the air as well. A mature tree can sequester 350 lbs. of carbon dioxide a year.
Trees can help mitigate floods caused by hardscapes like roads, driveways, and sidewalks. A mature tree uses about 5,000 gallons of water a year, which would otherwise flow into stormwater drains, flooding them in heavy rains.
When trees are placed correctly around a home, they can reduce the energy needed to cool it in the summer by 30%. Deciduous trees can be planted on the southern sides of homes to shade them in the summer. During the winter, the leaves on deciduous trees have fallen so they do not intercept the weak winter sun. Evergreen trees can be planted on the northern side of structures to provide a wind break and a screen.
Fruit and nut trees provide food for humans and wildlife. They can be planted on city streets to improve the food available to people in food deserts.
Urban trees represent crucial food and habitat for insects, birds, and small mammals. Without them, urban areas would be bare of life. Trees can also serve as a bridge between habitats for birds.
People living near trees and other plants are healthier and happier. People who can see trees and other plants have lower blood pressure than those without access to green spaces.
A 2013 study found increased deaths from heart and respiratory illnesses in the 15 states where the emerald ash borer has killed the ash trees in the urban forest.
Urban Challenges for Trees
Trees planted in cities have an average lifespan of 20-30 years. For comparison, a white oak tree can live 600 years in the country, and red maples can live 75-150 years there. Urban trees must tolerate pollution, lack of space for roots, and pressure from diseases and pests.
In addition, urban trees are often planted where a city planner thinks they should go, without regard to sunlight, water, soil, and climate. Trees can’t thrive without having their basic needs met.
Improving the Health of Urban Trees
Trees have the exact requirements in the city and the country. Before planting a tree, check what type of sunlight it needs, the amount of water required, how large it gets, and what kind of soil and soil pH it needs. Plant the right tree in the right place.
Trees that are planted by inexperienced planters are often put into the ground too deeply. The tree's root ball should be planted at the same level as the tree was growing before being harvested. Planting the tree too deep means its roots struggle to get the needed air. Ensure that the root flare – where the top root comes out of the trunk, is level with the top of the soil.
When you dig a hole for a tree, dig it two and a half times bigger than the rootball. Fill it with the soil you removed from the hole. If you fill the hole with amended soil such as potting, compost, or some other rich soil, the roots grow in a circle instead of spreading out. This eventually girdles the tree. Do not put fertilizer in the hole. It burns the small feeder roots that absorb most water and air. The tree may die. Even if it lives, the tree will struggle to get the water it needs, stunting it.
Urban trees must be properly pruned to stay healthy and avoid falling limbs. Never top a tree or cut off the branches and leave a stub. This is very bad for the tree. Prune trees to open up the canopy and improve air circulation. Remove damaged or diseased branches and water sprouts. Do not cut off more than one-third of the tree a season unless it is an emergency.
Trees need to be mulched. However, the mulch should not touch the tree. Leave a three-to-six-inch space between the tree and the first bits of mulch. The mulch should look like a bagel, not a volcano around the trunk. To provide the best outcome, use hardwood mulch to a depth of three inches. The mulch should extend to the edge of the canopy. If that is not possible, extend it as far as possible. Mulch keeps the soil cooler and moist, making the soil more hospitable for the tree. A layer of mulch around the tree also protects it from being hit by a mower or string trimmer, both significant sources of tree injury.
Make sure you space trees for their mature size. Don’t plant the tree too close to buildings or sewer lines. The roots will damage hardscapes as they try to expand. Do not plant a tree over 20 feet tall under power lines at maturity.
Choosing Trees for Urban Areas
The exact species of tree that will do best in your landscape varies by where you live. Native species of trees will be best able to adapt to living in urban environments. For example, sweetgum, redbud, and river birch are good choices, depending on the habitat you have in your landscape. Your extension agent can give you a list of trees that do well in your area.
Author: Tammy Sons, an experienced garden writer and plant expert with over 30 years of experience, shares her gardening expertise. She offers helpful advice and care tips specifically for native plants. She is the founder and CEO at TN Nursery:https://www.tnnursery.net
