The Scientific Benefit of Trees: A literature review

 

 

 

By 2050, an estimated 66% of the total world’s population will be urban¹. Urbanization, coupled with a changing climate, is a challenge on a global scale that greatly impacts the health and well-being of humans. In order to establish healthy and vibrant communities, trees need to be part of the global discussion. Over the past 30 years, science has demonstrated how trees in our landscapes benefit people and that well-maintained trees are an important asset to keep a community healthy and safe. Planting and maintaining trees, as part of urban planning and engineering solutions, can serve as a nature-based solution to many challenges communities face: managing stormwater, supporting mental and physical health for people, reducing crime, addressing pollution, and providing wildlife habitat. Despite the critical importance or urban forest, urban tree cover continues to decline nationwide each year ².

 

Investing in trees through planting, care, and maintenance will produce a significant return on investments, especially as older and larger trees provide the most benefits³. Trees are a long-term solution for many issues people face and they are a valuable resource for every community, especially those in urban or suburban settings. Botanical gardens and arboreta play an important role in this pursuit for a healthy and vibrant urban forest. These institutions provide valuable insight and leadership due to their expertise in botany and horticulture, as well as an established track record of public outreach and training. The future of urban forestry should focus on protecting large trees, as well as improving age structure, standards and planning management.

 

While not comprehensive, this list provides an overview of the many scientific benefits that trees, and greenspace with trees, provide to people both directly and indirectly.

 

 

Experts suggest that every dollar invested on tree planting and management can result in a high return on investment ^4,5, even as high as over 500%⁴. The compensatory value of the urban forest in the continental US is estimated to be worth more than $2.4 trillion⁶, with $18.3 billion worth of ecosystem benefits occurring annually⁷. Trees and greenspace provide important direct and indirect benefits social and biological benefits ^8,9, such as:

 

● Reducing stormwater runoff ^10–12

● Reducing air and water pollution^13–17

● Reducing energy costs and use associated with heating and cooling^18–21

● Reducing the urban heat island²²

● Protecting roadways and reducing the amount of asphalt sealers required ²³

● Reducing noise pollution²⁴

● Providing valuable carbon storage and sequestration ^25,26

● Increasing food security of urban areas ^27,28

 

Trees stimulate the local economy The presence of well-cared for trees encourages shoppers to spend more time at a business district, and they will travel a greater distance to visit that center, research has shown. Further, shopping areas with trees are more likely to be ranked as being more comfortable and having better upkeep, friendlier staff, and higher quality products²⁹. Additionally, having well-maintained trees along city streets and retail areas, as well as in residential areas can:

 

● Increase rental rates of business properties³⁰

● Increase the sale price of a home^31–34

● Decrease the time a house is on the market³⁴

 

 

The presence of trees and green space on people can:

 

● Increase attention, memory,35,36, reflection37 and focus³⁸

● Reduce stress39 or increased ability to recover from stress⁴⁰

● Increase life satisfaction41 and positive thoughts or emotions^42–44

● Lower mortality rates from non-accidental deaths^45–47

● Shorten recovery times in the hospital48 and increased perception of health⁴⁹

● Increase physical activity⁵⁰

● Reduce diastolic blood pressure⁵¹

 

Children and students benefit from the presence of trees, which can:

 

● Reduce symptoms of attention deficit disorders52,53 and increase attention^54,55

● Increase in classroom engagement⁵⁶

● Improve test scores in reading and mathematics⁵⁷

● Improve the mood of teenagers and lower their emotions of depression, anger, and fatigue⁵⁸

● Increase self-discipline, impulse inhibition, and concentration in young girls⁵⁴

● Improve physical health⁵⁹

 

 

Trees evoke positive strong emotions in people⁶⁰. Urban residents value trees 61 and people like looking at trees⁶². Well-maintained trees can reduce crime in a neighborhood. In fact, the loss of trees in neighborhoods due to pest infestation has been positively associated with increases in crime⁶³.

 

This phenomenon of trees reducing crime rate has been observed in numerous studies:

 

● Well-maintained trees are related to lower crime rates^64–66

● A green view from a home can lower aggression and violence in that home⁶⁷

● Well-maintained trees are related to reduced property crimes and violent crimes⁶⁸

 

Trees encourage people to gather in common outdoor space, causing:

 

● Increased social capital^69,70 and ultimately increased supervision of children⁷¹

● Increased sense of community and safety^69,72,73

 

 

Large, old trees are critically important worldwide from an ecological and cultural perspective³. Despite their importance, these trees are declining globally⁷⁴. While trees in natural environments can survive for 100’s of years, the half-life of an inner street tree is 10 to 15 years⁷⁵. It is difficult to develop a universal definition for a large, old tree³, largely given the diversity of tree species worldwide^3,76, so there are limited management and conservation plans³. Nevertheless, emphasis must be made to preserve large, old trees as they provide numerous benefits³, especially in urban environments⁷⁷. Once large old trees are lost from the community, it is difficult if not impossible to replace their cultural and ecological function ³.

 

Large trees provide critical benefits for their role in:

 

● Creating habitat for other species^3,77,78

● Managing important environmental cycles and processes ³

● Storing and sequestering significant amounts of carbon⁷⁹

 

 

 

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