The worth of trees

From carbon sequestration to stormwater remediation, trees have many hidden environmental and economical benefits. ForestWander Nature Photography

Growers know the benefits of trees, but how can those benefits be translated into something that anyone can understand? When city or community budgets are tight, money for urban forestry—planting and maintenance—tends to be hit first and sometimes hardest. The same goes for regular community members thinking of upgrading their landscape. That’s why it’s important to convince community stakeholders that the trees in your community have economic and environmental value.

Well, city and community planners understand money. And so does any regular Joe or Jane who is in charge of their family’s finances. So you need to show them why they should make room in their budget for tree planting and maintenance.

Carbon sequestration, storm water remediation, energy savings, the Green Cities Initiative, and the dangers of invasive species: these are all hot buzzwords, and they can be excellent examples of why trees matter.

“We know trees are worth energy savings, and that’s a big deal right now,” said Pamela Bennett, Ohio State University Extension Master Gardener Volunteer Coordinator. “Green Cities and LEED certification, becoming more sustainable. Your community is probably very focused on storm water remediation; it may have even been mandated to take care of your storm water. Invasive species is another key topic we need to address. This package of tools has the ability to take the data you gathered the inventory and measurements of trees and turn it into dollars and cents benefits of these trees.”

Bennett uses a software suite called i-Tree and the National Tree Benefit Calculator to quantify the value of these hard-to-measure categories. The i-Tree suite of tools was developed by the USDA National Forest Service and several collaborators. Since its initial release in 2006, numerous communities, non-profit organizations, consultants, volunteers and students have used i-Tree to create detailed reports on individual trees or full forest assessments. The i-Tree software is free, and available for download from its website (www.itreetools.org).

The National Tree Benefit Calculator (treebenefits.com/calculator) was co-developed by Davey Tree Expert Company and Casey Trees. It is designed to be a simple, accessible tool to estimate the environmental and economic value trees provide on an annual basis. Just enter your zip code and it will provide tree values in your area.

Value-added
As an example, the overall benefits of a 36 inch pin oak tree in Washington, D.C. are $265 every year. If you use the i-Tree model, it will break down the benefits by category. For this tree, stormwater runoff reductions and property value increases account for the largest proportion of total benefits for this region. Stormwater runoff reductions were valued at $144.19 and the property value increase was set at $70.45.

Trees are especially important in urban areas because of their effect on stormwater runoff, Bennett said. Because of overworked sewer systems that can’t handle the load of a large storm and large expanses of paved roads, parking lots and other impervious surfaces, rainfall washes quickly into streams and rivers, carrying silt downstream. Large shade trees act as mini-reservoirs, controlling runoff at the source, reducing and sometimes eliminating those problems. Trees intercept rain on leaves, branches and bark, and infiltration is improved through the tree’s root system. The pin oak used in our example will eliminate 14,565 gallons of stormwater runoff this year.

Trees also increase property value while saving the property owner in energy costs.

“Realtors have always known trees out front of a home increase the ‘curb appeal’ but were never able to say how much,” Bennett said. “Now we know home buyers are willing to pay 3-7 percent more for a home with ample trees versus one with little or no trees.”

This model uses a tree’s leaf surface area to make this calculation. The tree’s LSA will increase as it ages.

Trees modify climate and conserve building energy use in three ways, Bennett said. First, shading reduces the amount of heat absorbed and stored by buildings. Second, evapotranspiration converts liquid water to water vapor and cools the air by using solar energy that would otherwise result in heating of the air. Third, tree canopies slow down winds. This helps reduce the amount of heat lost from a home, especially from areas where conductivity is higher, like glass windows. The same 36 inch pin oak will conserve 351 kilowatt/hours of electricity for cooling and reduce the consumption of natural gas by 9 therm(s), and reduce atmospheric carbon by 1,022 pounds.

Carbon sequestration is another big sustainability buzzword. How significant is this number? According to Bennett, most car owners in an “average” car (mid-sized sedan) drive 12,000 miles generating about 11,000 pounds of CO2 every year. Trees reduce carbon in two ways: they sequester CO2 in their roots, trunks, stems, and leaves while they grow and in wood products after they are harvested. Second, trees near buildings can reduce heating and cooling demands, reducing emissions associated with power production.

Invasive species are another hot topic, especially in states that have experienced the Emerald Ash borer. Bennett said her i-Tree studies have shown a disturbing lack of diversity of our tree canopy.

“When you see it on paper, it really hits you in the face that we have an awful lot of ash trees or maples, or both, and we need to do a better job of planning,” she said. “Looking at invasive species wasn’t our goal when we started the tree surveys, but it rose to the top after we looked at it.”

Survey says…
It’s useful to know what economic and environmental benefit one tree can have, but the software really shines when providing tree data for entire neighborhoods, cities or states. Of course, to have that data, you need to conduct a tree inventory.

For communities, the best way to do a tree inventory is by utilizing volunteer groups or organizations. Master Gardener volunteers, boy scouts or girl scouts, 4-H or church groups, or green industry companies like growers or garden centers can help, because these surveys take time as well as manpower.

Nurseries should have an especially keen interest because they know the value of trees and the need for greater diversity in what’s planted.

“They are going to get feedback, PR, and potential tree sales,” she said.

The volunteers identify and measure trees for the inventory. If you don’t have Master Gardeners on hand, then you may need to train volunteers to ID trees, use a Biltmore stick or diameter tape to take measurements. Providing field guides is a good idea, too.

After the survey is done, the data is analyzed through the software. One of the tools is a a cost/benefit analysis. For instance, the city of Toledo, Ohio did a tree survey and determined the total benefit was $15 million, with a cost/benefit ratio of 366 percent.

“You’re not going to get that kind of ratio anywhere else than trees,” Bennett said.

Toledo’s trees accounted for 665 million pounds of stored carbon, a total of almost $5 million or $59 per tree. Many communities are looking to accumulate carbon credits. The data can be used for that purpose. The results also show you trees’ impact on air quality, carbon dioxide, energy benefits.

Most communities don’t have the money in their budgets to pay professionals to survey their trees. Bennett oversaw a survey in 2012 of the 15,445 trees in her hometown, Springfield, Ohio. She says a professionally-done survey typically costs $4 per tree. So by using volunteers, she saved $12,356.

The inventory helped Springfield’s city council understand why trees were vital to the community.

“When they look at the dollar value it really raises their awareness of trees’ value,” Bennett said. “They say ‘I had no idea we were getting this much back from our trees.’”

Bennett also saw the lack of tree diversity in her community.

“We had a lot of maples and ash trees,” she said. “Our community is also going to use this inventory to be able to estimate cost of taking down all ash trees due to EAB, because we are on the edge of EAB territory.”

Bennett plans to leverage the stormwater utility dollars reported in the tree inventory for future tree maintenance.

“A tree doesn’t start giving back until it is 30 years old,” she said. “So if you want your urban trees to do a good job, you need to get out of the mindset that you plant these trees, they die in seven years, and you replace them.”