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The Value and Management of Street Trees

The majority of Cook County is residential land. The amount of green, unbuilt area in residential neighborhoods is almost double what we have in publically-owned natural areas. This vegetated area is split fairly evenly between tree canopy cover and herbaceous vegetation, which is mostly turf grass. With such an abundant coverage in direct proximity to people’s houses, residential nature is arguably the most common interaction people have with their environment. This is a double-edged sword. On one hand, it is important for people to feel connected to their land, and ownership helps promote land care. On the other hand, this large land expanse is essentially the sum of individually-managed parcels. Individual households manage their land differently, which results in a fine-scale patchwork across the landscape.

Aside from requiring that areas be up-kept, it is very difficult to manage privately owned land for environmental benefits on a large scale. Street trees, which are planned, planted, and maintained by the municipality, are an excellent method by which cities and townships can help connect individual land parcels by exerting some overarching environmental management.

Street trees are more than just beautiful additions to our urban landscapes. They are hugely beneficial to ecological, social, and economic function in cities. These three facets are the three pillars of sustainability; a major focus in urban development in light of climate change. While there are many other aspects of sustainability planning, street trees are generally a popular and well-received aspect of municipal land management.

Street trees are critically important to the ecology of urban areas. Trees in the parkway help ameliorate some of the most pressing environmental concerns that affect people, such as stormwater runoff. Unlike in natural areas where rainwater infiltrates rapidly, rain that falls in cities often lands on impervious surfaces. When this happens, the water must flow until it finds a low point or a storm sewer, picking up pollutants as it goes. Street trees—especially large ones with established canopies and roots—help prevent this from happening. Water that falls on leaves and stems is intercepted, where it will either evaporate back into the atmosphere or it will flow along the branches toward the stem, ultimately entering the soil at the base of the trunk. Below ground, a tree’s network of roots are simultaneously taking up soil moisture, which increases the infiltration rate and aids in preventing flooding.

Socially, street trees make areas safer. Interestingly, accidents—particularly those that result in incapacitating injury or fatality—are much less common on streets that are lined with trees. This is a complex social reaction to an inherent human preference for natural-looking spaces. Researchers believe that the reduction in serious accidents is a combination of several factors. Firstly, tree-lined roadsides provide a more definitive boundary for the road, which helps drivers maintain control and respond more quickly. Furthermore, street trees reduce the mental and physical stressors of drivers commuting in urban areas. People are more willing to take the slower, longer scenic route if it has beautiful trees along the roadside, which also alleviates traffic on main thoroughfares. The safety of an area doesn’t just increase for drivers. Neighborhoods that have higher vegetation and tree cover experience less crime than less treed neighborhoods; this trend is true for both property crimes and violent crimes.

Installing street trees has a fairly high return on investment, especially when we look at their capacity to provide economically-valuable ecosystem services. In the United States, trees in urban areas store over 600 million tons of carbon and sequester another 25 million tons annually. These benefits total over $50 billion dollars annually, just in terms of carbon mitigation. Street trees also dramatically increase residential property values. A comparison of sales of comparable homes on treed and un-treed streets demonstrated that homes on treed streets sold for approximately $10K more, and averaged two fewer days on the market. Businesses also benefit because customers are willing to travel farther and spend more time shopping in treed districts.

But, for all of their benefits, being a tree in the city is hard! Ambient heat, human-inflicted damage, anthropogenic pests, and soil compaction are a small sample of the challenges that trees in cities face. However, best practices in urban forestry can help alleviate these stresses. Increasing the size of new tree pits, selecting hardy native species, and constructing grates or fencing to protect vulnerable roots and trunks goes a long way to protect the planting investment and maximize potential benefits. As land managers and city planners in and around Chicago continue to plant and manage street trees, we all benefit.

If you love trees and want to protect them, consider becoming a Tree Health Monitor. Monitors assess tree health using a nationally recognized protocol developed by The Nature Conservancy and the USDA Forest Service. Contact Volunteer.FPD@cookcountyil.gov for more information.

Article by Elsa Anderson, stewardship program aide.