Seriously Cool Science: Estimating the Carbon Cost of Producing Trees in the Nursery

Posted by: Alison O’Connor, horticulture agent, CSU Extension in Larimer County

I spend a lot of time reading scientific journal articles. Now, before you make your assumptions and claim that I’m a weird, unsocial hermit, remember that I’m also a student and working on my PhD in horticulture at CSU. Reading published work comes with the territory and it’s not as bad as you think—and it also keeps me up-to-date as an Extension agent. But there are many days that I feel like Elton John’s Rocket Man: “…And all this science I don’t understand; it’s just my job five days a week.”

Not my beagle, but still cute!

There are many top-notch researchers in horticulture…people I admire and secretly stalk in a non-creepy way…and I’m always grateful to find articles that relate to my study. There’s something really satisfying about tying together another’s research with my own and helping me prove (or disprove) my research findings.  But I can only think of a couple articles that get me so excited that I bring them up to anyone who will listen…my dental hygienist (“Moooah…muhha…trees.”), my mother (“Uh huh…that’s nice Al.”), my beagles (who are excellent at looking the part with their heads cocked to one side)….  One such article was just published in September 2013:

Ingram, D.L. and C.R. Hall. 2013. Carbon footprint and related production costs of system components of a field-grown Cercis canadensis L. ‘Forest Pansy’ using life cycle assessment. J. Environ. Hort. 31(3):169-176.

This study, in my eyes, is brilliant. Dewayne Ingram (University of Kentucky) and Charles Hall (Texas A&M) attempted to answer some simple questions: How much carbon does it “cost” to produce nursery trees?  And does the carbon “cost” offset what the tree “absorbs” in carbon?

Carbon. Everyone talks about it and it’s currently popular to try to be “carbon neutral.”  That means that the carbon (carbon dioxide and other greenhouse gases) it takes to produce a product will be equally offset by the amount of carbon the product stores.  Many major companies and organizations have posted their carbon footprint for products or services.  Timberland, maker of your hiking boots, has an average carbon cost of 40 pounds of CO₂ per product.  Compare that to Patagonia’s Talus jacket, which is 66 pounds of CO₂. New Belgium Brewery, located in Fort Collins, has their beer production down to science: a 6-pack of Fat Tire comes in at 7 pounds of CO₂. 

Photo from www.craftbrewingbusiness.com

But finding the carbon footprint of trees…why is it necessary? Trees are touted as the carbon-munching beasts of the landscape.  We, in part, plant trees, to offset carbon being spewed into our atmosphere.  Trees are good. Trees are green. Trees beautify our landscapes. Trees need carbon to complete their essential process of photosynthesis. Trees are a win-win.

But it does take carbon to produce trees. Something I never really thought about.  But yes, trees are produced using equipment, fertilizer, herbicides, etc.—which all release carbon dioxide into the atmosphere. But no one, until Ingram and Hall, had looked carefully at the carbon production costs of producing trees in the nursery. Their study can help nursery producers locate areas of production where they may be able to reduce carbon inputs. And this is what they found:

By using ‘Forest Pansy’ redbud as one example (they also studied maple and blue spruce), they found that the total carbon input to produce a redbud from seed to landscape “costs”

Trees being loaded for transport at Van der Berk Nurseries
www.vdberk.co.uk

about 30.2 pounds of CO₂.  This includes everything that goes into producing the tree: equipment, chemicals, loading and unloading the tree, harvesting, etc. They found that about 1/3 of the total carbon input was from loading and unloading the tree.  They also accounted for the carbon that the tree stored during production (~23 pounds of CO₂). 

But then these clever researchers took this study a step further…they estimated how much the tree would sequester in carbon during its lifetime.  And this is where things get incredibly interesting. One thing to keep in mind is that the average life of a landscape tree is only 8 years. There are numerous reasons for this, but basically, the majority of our landscape trees don’t become the shade under which our children will lay.

Photo from Mark Adams, Adams Arbor Care, LLC
www.bugwood.org

Being optimists and knowing that some trees do live beyond 8 years, Ingram and Hall used the hopeful number of 40 years (the estimated long-term life of a redbud). Over a 40-year lifespan, the estimated carbon sequestration of redbud was 323 pounds of CO₂. That means, the tree is doing exactly what we expect trees to do…offset carbon inputs into the atmosphere by storing a greater amount of carbon than it took to produce it.  But what about when that tree eventually dies? Let’s not forget that it takes carbon to remove it…by using equipment. So Ingram and Hall took this into account as well. They estimated carbon released when driving to the site, running a chainsaw, running a chipper and then moving the mulch. All told, to remove a mature redbud, there is a release of 194 pounds of CO₂ into the atmosphere. So the tree absorbs 323 pounds of CO₂ during its lifetime, but it takes 194 pounds to remove it from the location. A net benefit of 129 pounds CO₂ stored by the redbud during its lifetime.  Not bad, but only about three pairs of Timberland boots.

Let’s go back to that average life of a landscape tree. Again, most trees don’t live to be 40 years old. Based on information that Dr. Ingram shared with me, in order for the tree to be carbon neutral in its life (from seed to death), the tree has to live an estimated 22 years—almost 3 times as long as the current average.

So what does this mean? Well, several things. One is that we need to do a better job of producing, planting and maintaining trees to last longer in our landscapes. Another is that Ingram and Hall’s study can be crucial to a grower who is looking to not only save money on production costs, but to be more environmentally responsible. Part of the article focuses on reducing carbon inputs, like driving trees a shorter distance to a job site (driving 240 miles vs. 120 miles reduces carbon inputs by half, to ~4 pounds of CO₂). Eliminating a year of production on the tree can reduce carbon by 2.6 pounds of CO₂ per tree (from 4 years to 3 years). All important evidence a grower can use to make his/her businesses more economical and viable. Plus, let’s face it…don’t you think marketing a “sustainable” tree would be appealing to consumers?

I also think that this article is timely with the recent detection of emerald ash borer in Boulder. If we lose the majority of our urban ash forest due to this insect, a tremendous amount of carbon dioxide will be released in their removal, but also to replace them with other trees. And we lose the carbon absorption benefit from those dead, removed trees. That reinforces why it’s even more important to ensure that our newly planted trees survive, to help offset some of the potential new carbon emissions in our atmosphere. Whoa.

Seriously.Cool.Science.