Ecosystem Services of Urban Trees

We have been reading about and discussing the importance of forests for providing habitat for native species and ecosystem services for humans, such as flood control, air pollution mitigation, cooling/shading, and carbon sequestration. For this field activity, you will measure and identify 3 trees near your house or on campus, and then calculate and compare their benefits using an online model developed by the US Forest Service.
Field activity preparation. Please read this section before going out into the field.
For the field portion of this activity, you will need to find 3 trees, identify them, and then measure their diameters. These trees can be located anywhere, though I would like for you focus on cultivated areas rather than natural areas. For example, find trees that are growing in an urban park, your front or back yard, on a city street, or on the St. Edward’s campus. They should be three different species of trees.
Tree Identification: You should have already created an account with iNaturalist, and that app will be helpful during this activity for identifying the trees. You may also want to search for and download any online tree guides available for your area.
Tree Diameter: To measure tree diameter, you can either use a regular tape measure and then calculate the diameter later, or you can make your own “DBH tape” or “diameter tape”. Diameter tapes are calibrated so that wrapped around a tree, you can get a direct reading of the circumference rather than the diameter. They are based on the geometric formula:
d = C/pi
where d= diameter; C = circumference; and pi = 3.14

To make a diameter tape,

1. Cut a 31.4-inch strip of flagging tape (or paper)
2. Divide into 10ths
3. Draw lines at each 10th
4. Mark each line: 0, 1, 2, 3, 4, and so on
   Further instructions about how to use a diameter tape in the field will be given below.
   Field checklist.
   Before heading out to the field, make sure that you….
   o Read over, print and/or download the instructions for the activity
   o Bring a notebook (or a way to take notes), camera/phone, and water
   o Bring a tape measure or a diameter tape
   o You may also want to bring/wear: bug spray, a sunhat, sunscreen, and sturdy shoes
   Part 1. Collecting Tree Data

Choose 3 trees to measure and compare.
Be strategic about which trees you will measure because you will need to come up with hypotheses about what you might find. For example, which of the three trees do you think provides the greatest benefit in air pollution mitigation? Which tree do you think provides the greatest benefit in cooling and shading, and thereby reducing energy bills, if you were to plant it by your house? The three trees must be three different species.

Once you have identified the trees, you will have to measure their diameter at breast height (DBH). Wrap your diameter tape around the trunk at a distance of 4.5 above ground level and record the diameter to the nearest ½ inch. If your tree has multiple trunks, just measure the biggest one. If you have a measuring tape, you will need to calculate the diameter later from the equation d = C/pi.

For each tree, collect the following information:

Tree 1
Species: ________ Diameter (DBH): _________

Is it growing in a cultivated/ ornamental or natural area?

How much area would you estimate the crown of the tree is covering in square feet?

What do the leaves looks like?

Take a photo of the whole tree and insert it here:

Take a photo of the leaves and insert it here:

 
Tree 2
Species: ________ Diameter (DBH): _________

Is it growing in a cultivated/ ornamental or natural area?

How much area would you estimate the crown of the tree is covering in square feet?

What do the leaves looks like?

Take a photo of the whole tree and insert it here:

Take a photo of the leaves and insert it here:

Tree 3
Species: ________ Diameter (DBH):_________

Is it growing in a cultivated/ ornamental or natural area?

How much area would you estimate the crown of the tree is covering in square feet?

What do the leaves looks like?

Take a photo of the whole tree and insert it here:

Take a photo of the leaves and insert it here:

Part 2. Hypothesis Testing
You will be calculating the following ecosystem services associated with the three trees: carbon sequestration, property value, electricity savings, air pollution mitigation, and stormwater mitigation. Come up with 2 hypotheses that you can test with your data and give a short justification for each one. For example, “I predict that tree #1 will be better at reducing heating and cooling costs than tree #2 because it has a much denser canopy”.

Hypothesis 1:

Hypothesis 2:
Part 3. Calculating Ecosystem Services of Urban Trees
With the DBH data and species information you collected, you can now use the National Tree Benefit Calculator to calculate ecosystem services and test your hypotheses. According to a tree’s DBH, there are allometric equations that have been developed to determine its biomass and carbon storage potential. The USFS has developed a model that use these equations and others to estimate a whole range of other benefits, including air pollution mitigation, storm-water diversion, and energy savings from heating and cooling. These numbers vary by species, which is why it was important that you correctly identified the trees that you measured.

To calculate your trees’ benefits, take the following steps:

1. Go to the National Tree Benefit Calculator: http://treebenefits.com/calculator/index.cfm.
2. Enter the zip code of which corresponds to the data collection location. If you are not in the US, use the map feature. Click on “Select a location from the map” and then choose the zone that best approximates the climate where your trees are located.
3. For each tree, select the tree species from the dropdown menu. If the tree species is not available on this list, choose the closest relative. If there are no related trees on the list, choose the type of tree it is under “Other”. You will need to know if it is a broadleaf or conifer, deciduous or evergreen, or palm.
4. Enter the DBH in inches of the tree species.
5. Select “single family residential” as land use type from the dropdown list. Even if your tree is located in a park, we will pretend that it is near a housing unit because otherwise you won’t get to see the potential energy savings or property value. The model gives similar numbers for Single family, multi-family, small commercial, and industrial for energy savings, but property value changes. To standardize, we will all use the same location type.
6. Select “Calculate”
7. Record the cost values provided by this tree in the following table according to these guidelines:
   • Total savings- this appears as a dollar amount on the first tab “Overall Benefits”
   • Strom water - click on the second tab and enter the number in gallons of stormwater that your tree will intercept
   • Property value - click on the third tab and enter the dollar amount that this tree will add to your property value per year
   • Energy - Click on the 4th tab and enter the number for total kwh of savings in energy use through cooling
   • Air quality - Click on the first tab “Overall Benefits” to get the total savings for air quality mitigation from the pie chart. Then, click on the 5th tab and estimate the savings associated with the first column - ozone.
   • CO2- Click on the CO2 tab and enter the number of pounds of carbon that this tree will reduce atmospheric carbon by through both direct sequestration and avoided emissions.

Tree Species DBH (in) Total savings $/year Storm
water (gallons) Property value
($) Energy (kwh) Air quality (total $) Air quality- O3 ($) CO2 (pounds)

8. Once you are done calculating your three trees’ savings, set the diameter of three trees at 20 inches to compare what their value would be if they were the same size. Enter the data here:
   Tree Species DBH (in) Total savings $/year Storm
   water (gallons) Property value
   ($) Energy (kwh) Air quality (total $) Air quality- O3 ($) CO2 (pounds)
   20
   20
   20

Part 4. Evaluating your findings

1. Which tree provided the greatest overall benefit? Was this surprising? Why or why not?
2. Which tree provided the greatest benefit for air pollution mitigation? Is that what you would expect based on their leaf shape and/or size? Why or why not?
3. Did you find that your hypotheses were supported by your data? If not, what could explain your findings?
4. When you calculated the savings of your 3 trees at the same diameter, were your findings surprising? Why or why not?
5. Lastly, as explained in the “About the Model” tab, this model is intended to be simple and accessible, and give a basic understanding of the environmental and economic benefits that trees provide on an annual basis. What are the limitations to this kind of a model, and what do you think it could or should be useful for, if anything?