Monthly Archives: July 2022

“I never saw a discontented tree.” ― John Muir 

Trees work hard. From taking the heat to covering the street, from helping our health to growing our wealth, entering a tree-lationship can be good for you – and your city – in more ways than one. So, if you take care of your trees, they’ll really take care of you! 

Here are eight research-backed ways to prove that trees are excellent neighbors.  

1. They fight crime. Research₁ indicates that a 10% increase in tree canopy can be associated with a roughly 12% decrease in crimes such as robbery, burglary, theft and shootings. 

2. They keep us cool. Trees can cool cities by up to 10 degrees, fighting off the heat island effect and preventing heat-related illnesses in urban areas like Denver. This comes from cooling and evaporation,₂ not just shade.  

3. They save us money. Trees properly placed around buildings can reduce air conditioning needs up to 30% and can save 20–50% in energy used for heating. By providing protection from the sun and wind, trees can reduce energy costs by as much as 30%. Urban tree cover supplies heat-reduction services worth $5.3–12.1 billion annually.₃ 

4. They might make us feel better. Research has shown that spending time around trees and nature can reduce depression and anxiety. One study₄ suggests that unintentional daily contact with nature through street trees close to the home may reduce the risk of depression, especially for individuals in under-resourced communities. 

5. They help us breathe. One large tree can provide a day’s supply of oxygen for up to four people!  

6. They keep us healthy. In some cases, just seeing trees does the trick! Often cited as one of the earliest studies₅ of the possible relationship between access to greenspace and health: surgery patients with windows overlooking natural views had shorter postoperative hospital stays!  

7. They even clean our air! In one year, an acre of mature trees absorbs the amount of CO₂ produced by a car driven 26,000 miles.  

8. They can make us money. Every dollar spent planting and caring for a community tree, yields benefits that are 2X to 5X that investment! Healthy trees can boost your property’s value by 5 to 20%.  

 Because as the Lorax, who spoke for the trees, once said, “Unless someone like you cares a whole awful lot, nothing’s going to get better. It’s not.”  

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1. Troy et al. 2012   
2. Rahman et al. 2020 
3. McDonald et al. 2020 
4. Marselle et al. 2020 
5. Ulrich 1984 

Other resources:  

• U.S. Forest Service: https://www.fs.fed.us/psw/news/2011/110308_arborday.shtml     
• National Arbor Day Foundation: https://www.arborday.org/trees/treefacts/     
• Colorado State University Extension: https://csfs.colostate.edu/colorado-trees/     

Trees are our first line of defense when it comes to combatting the urban phenomenon of the Heat Island. No, Heat Island isn’t a new reality show. Although it is a reality.  

What is a Heat Island? 

The easy explanation by NASA’s Climate Kids is that an urban heat island occurs when a city experiences much warmer temperatures than nearby rural areas. The difference in temperature between urban and less-developed rural areas has to do with how well the surfaces in each environment absorb and hold heat. Cities tend to have more impervious surfaces, such as buildings, sidewalks, roads and patios, which hold more heat.  

Cities throughout the world are experiencing urban heat islands, and Denver is no different. Take a look at Denver’s Heat Island map:

This map uses impervious surfaces as a proxy for heat. In this map, the darker colors represent hotter areas 

…and now take a look at the map of the city’s trees:  

In this map, the darker the color, the higher percentage of tree canopy cover there is. 

See how they are essentially opposites of each other? Meaning, the places with lower heat vulnerability are also the places with the highest tree canopy coverage. It’s clear to see that trees make a difference.  

Now that we know it’s this easy, what can we do? You guessed it.  

Plant. More. Trees.   

Now you may be asking, what is it about trees? It can’t just be the shade they offer. What else is taking place? It’s a great question with only a halfway-surprising answer. Because a lot of it does have to do with the shade they provide and the sunlight they deflect. But there is also something else happening that helps trees cool their surrounding area… 

Evapotranspiration.  

Over at USGS.gov (United States Geological Survey), a science bureau within the United States Department of the Interior, there is a simple illustration that says it all: Evapotranspiration simply describes how water working through the tree ends up cooling the air around it. Water (precipitation) comes in through the roots and is released as vapor (transpiration). And, as an added bonus, the soil releases even more water to cool the air down low (evaporation).

So, one of the best ways we can combat heat islands is by planting more trees. Two ways you can do that: apply for a free tree in your public right-of-way and plant more trees downtown.  

All of the above combined results in a drop in temps and a happier, healthier – and much cooler –community. If you’ve read all the way through and you still want to learn more, check out this PBS interview from 2021, featuring Denver’s own City Forester Mike Swanson talking about Heat Islands.