In several previous articles, I have written about the benefits of urban trees. Urban trees are defined as any tree located along streets, in parks, on your lot, or anywhere else people live in an urban or semi-urban area extending outward to the remnant forests or the outward edges of suburbia.
These benefits include shade for cooling our homes and reducing our energy consumption, sequestering carbon, reducing air pollution, reducing water runoff, providing wildlife habitat, producing oxygen, providing sound attenuation, providing aesthetic benefits, and increasing property values.
However, I have never attempted to quantify, in dollars, what these various ecological benefits contribute.
In recent years, several models have been developed to attempt to put a dollar amount on these ecosystem services. An article in the Spring 2021 Florida Arborist, the quarterly publication of the Florida Chapter of the International Society of Arboriculture, has summarized these benefits.
This article was written by a collaboration of authors from the University of Florida and the University of South Florida and is the basis for the information cited below.
Trees provide these benefits primarily based upon the size of their canopy. Larger trees such as live oaks provide greater benefits than smaller trees such as crape myrtles.
The tree canopy coverage of urban areas throughout Florida have been determined utilizing aerial photos and a “point-based” sampling methodology. A point either lands on a “tree or shrub” or “no tree or shrub” as viewed on an aerial photograph.
Tree canopy coverage varies from a low of 18.6% in the Okeechobee metropolitan area to a high of 74.4% in the Crestview/Fort Walton/Destin metropolitan area.
In general, canopy coverage in Florida decreased from north to south and west to east.
The Ocala metropolitan area averaged 56.4% coverage, while the Homosassa Springs metropolitan area (all of Citrus County) averaged 55.3%. This means that 56.4 and 55.3% of the land area is covered by tree or shrub canopy.
These averages placed ninth and 10th, respectively, out of the 29 areas studied within Florida. These 29 areas represent 51 of our 67 counties, but 98% of the population.
Air pollution removal includes carbon monoxide, nitrogen dioxide, sulfur dioxide, ground-level ozone and particulate matter. The first three are a byproducts of the burning of fossil fuels, while the ozone is produced when sunlight reacts with air pollutants.
Trees reduce these various pollutants by absorbing them through their foliage or capturing them on leaf surfaces. The ecosystem service models estimate that, within the 29 metro areas studied within Florida, trees remove over 600,000 tons of combined air pollution each year — saving Florida residents an estimated $605 million in air pollution health care costs.
These values have been quantified for the Ocala area and total $16.4 million and for Citrus County, $13.1 million.
Trees assist in stormwater runoff by capturing rainfall on their leaves and bark as well as absorbing water into the soil in which they are planted. The trees within the 29 metropolitan areas collectively absorb an estimated 50 billion gallons of water, resulting in a savings of over $451 million in avoided stormwater-treatment costs.
For the Ocala area, this total is $11.5 million and for Citrus County, the total is $6.6 million.
However, the largest cost benefit of trees is in their ability to absorb carbon dioxide, also known as carbon sequestration. Trees utilize carbon dioxide in the process of photosynthesis and store it as carbon in their trunks, branches and roots.
This carbon storage continues during the life of the tree. In total, Florida’s urban forests sequester a total of 65 million tons per year of carbon dioxide equivalent, which equates to an estimated $3 billion in annual benefits.
Over their lifetime, these urban forests will provide an estimated $76 billion worth of carbon sequestration as these trees continue to grow and store more carbon.
The estimated annual benefit of this carbon storage is $135.8 million for Ocala and $49.4 million for Citrus County. The total carbon storage value for Ocala is $3.4 billion and for Citrus County, the total is $1.2 billion.
Please remember the values presented here are estimates derived from scientific modeling. They are based on the best available science and are important for estimating the ecosystem services provided by our urban forests, but should not be taken as absolute.
It is also important to remember that ecosystem services increase as tree canopy size increases. Thus, protection and proper management of our urban forest is vital if we are to realize the full benefits that trees provide.
Eric H. Hoyer is a certified arborist, a certified forester, a registered consulting arborist and a qualified tree risk assessor with Natural Resource Planning Services Inc. He can be contacted at firstname.lastname@example.org.