About the Urban Forest: Environmental Benefits of Street Trees
Next to its people, trees are arguably the most important resource in Santa Monica. The City’s forest is actually a green element of its infrastructure and requires regular care just like streets, sidewalks, utilities and public buildings. Our trees work for us day and night year round, continually improving our environment and quality of life. Santa Monica’s forest provides environmental benefits in the form of improved air quality, reduced energy costs, reduced storm water runoff into the ocean, sequestered carbon in their woody mass, shaded streets to extend the life of the asphalt surfaces, and reduced irrigation usage for front yard landscapes. And, as if that isn’t enough, trees increase in value, providing more environmental benefits the older and bigger they get.
Improving Air Quality & Squestering Carbon
The Greenhouse Effect is created when heat from the Earth is trapped in the atmosphere as a result of increasing levels of carbon dioxide (CO2) and other gases that prohibit it from releasing heat into space. Trees remove, or sequester, CO2 from the atmosphere during their photosynthetic process to form carbohydrates stored in trunks, branches, leaves and roots. The byproduct of this process is oxygen that is released back into the atmosphere. Even though Santa Monica is a coastal city benefitting from cool ocean breezes, the shade that trees provide for homes and offices reduces the need for air conditioning during the summer or when the Santa Ana winds blow into town. This reduces the demand for electricity during periods of hot weather. The combination of the cooling effect that reduces energy consumption, the removal of CO2 from the atmosphere and carbon storage in wood, makes trees a very efficient tool in fighting the greenhouse effect.
- Trees are an essential tool for removing carbon from the air. It is in their trunks, branches, leaves and roots while releasing oxygen.
- Planting trees remains one of the cheapest, most effective means of drawing excess CO2 from the atmosphere.
- A single mature tree can absorb carbon dioxide at a rate of 48 lbs/year and release enough oxygen back into the atmosphere to support 2 human beings.
- Trees remove gaseous pollutants and particulate matter from the air by absorbing them with normal air components through their leaf surface. One only has to take a handful of foliage from a street tree and rub their fingers over the leaf surface to see how this actually works.
- Mature street trees can reduce as much as 60% the particulate matter that is in the air around them.
- It has been estimated that a total of 300 trees can counterbalance the amount of pollution one person produces in a lifetime.
Protecting Water Quality
Trees are natural pollution filters that help improve water quality in Santa Monica Bay. They slow down stormwater runoff and ensure that our groundwater supplies are continually replensihed. Tree canopies interrupt rainfall, while tree roots, trunks and surrounding soil remove particulate matter such as nitrogen, phosphorus and potassium from runoff before it reaches the ocean. The USFS estimates that for every 5% of tree cover added to a community, stormwater runoff is reduced by approximately 2%.
Trees act as natural air conditioners that lower air temperatures and reduce heat islands created by paved areas and tall buildings. They provide buildings with shade in the summer and block winds in the winter, which reduces energy use and costs associated with indoor cooling and heating.
- The evaporation from a single large tree can produce the cooling effect of 10 room size air conditioners operating 24 hours/day.
- The USFS estimates the annual effect of well-positioned trees on energy use in conventional houses at savings between 20-25% when compared to a house in a wide-open area with no trees.