Your Urban Carbon Capture Farm

I’ll admit it. I sometimes feel like we are all in the bucket and the bucket is going straight to… a really hot place. Oh wait, Earth in 30 years. I feel helpless, like there is nothing I can do that will alter the current trajectory we’re on. As it turns out, there is something we can all be doing to mitigate atmospheric carbon dioxide levels, and we better start doing it right now because we’re running out of time. 

It’s called carbon farming, and we could be doing it in our own yards. If we were to individually practice this method on a global scale, it could prove an effective tool in helping mitigate global warming. 

Upon researching carbon farming, I had a duh moment. The opposite of aha; because it involves no exotic solution, no strategically engineered machines or parts. In fact, it is extremely simple and very familiar to us, and it involves the photosynthetic process of trees and plants. But before we get into that, there is something we are currently doing in our yards that isn’t helping the situation of global warming at all. 

One Gas Mower Pollutes As Much As 11 New Cars
There are 22,000 households in Corvallis, according to data, and the average yard size for the state of Oregon is 9,071 sq ft, using Lawn Starters numbers. Of these, many still have sizable lawns, and that can prove problematic for the planet. 40.8 percent of Oregonians mow their lawn once a week, and 31.2 percent mow biweekly. That is significant because, “one gas mower running for an hour emits the same amount of pollutants as 11 new cars driving 55 mph for the same amount of time,” states the EPA. That is a lot of carbon making its way into the atmosphere, and not a lot we get in return besides a place for the neighbors’ dogs to visit. 

We spend a lot of money on lawn care too. We purchase fertilizers and herbicides (which cause serious environmental problems in themselves). We pay water bills. And, if you don’t mow your own lawn, the average cost for a weekly mowing service in the state is $42.51. That is $170.04 every month during the growing season. 

Okay, so they’re expensive and a bit of a time sink. Is that it? Why do lawns get such a bad rap? 

Studies show that lawns, and the way we care for them, are causing a lot of environmental problems. Urban turf practices produce large amounts of greenhouse gases through fertilization, irrigation, and emissions generated by fuel combustion. Of particular concern, is the greenhouse gas nitrous oxide (N2O), which was found in a study by Amy Townsend-Small and Claudia I. Czimckik, to be released through urban turf practices in “significant amounts.” This is important to note because N2O is known to be 300 times more effective in terms of trapping heat in the troposphere than carbon dioxide. Just to be clear; that is really, really bad.

Another important reason lawns have lost their popularity among environmentalists is that they are inefficient at carbon sequestration. Carbon sequestration is the process of capturing and storing atmospheric carbon through the use of plants, soils, geologic formations, and the ocean. 

All plants sequester carbon, but some are better at it than others. The main consideration is that the biomass (the total volume of organic matter in a given area) of an urban lawn is relatively small, especially because for most homeowners, like my husband, allowing the grass to get higher than the lawn mower causes a special type of stress I will call, “Meadow-Dread”. Yet, it is biomass that determines a plant’s ability to photosynthesize and trap carbon. The smaller the plant, the less carbon it removes. In other words, lawns make a huge mess and they don’t do a good job of cleaning up after themselves. 

Instead, Plant a Carbon Capture Garden
A possible solution to the environmental problem of the urban lawn is to plant a carbon capture garden instead. This gardening method, also known as carbon farming, is essentially a way of cultivating a power-packed greenhouse gas reduction and storage system through the utilization of the natural photosynthetic process of perennial plants and the implementation of a multistrata system. 

Er, ahem. In simpler terms; planting a sort of jungle-yard. You know that crazy house you lived nextdoor to with all the moss on the roof, the vines and ivy growing on the walls, and with so many shrubs and bushes that you couldn’t see the windows? In fact, you weren’t even sure anyone actually lived there? Turns out, they got it right. Well, sort of. 

To help explain what a carbon-capture garden is, I went to Eric Toensmeier. He is the author of The Carbon Farming Solution, and is recognized as an expert in the field of permaculture and biosequestration. 

Carbon farming uses the rule of agroforestry (a method of integrating trees and shrubs into a farming system), and the system of permaculture (permanent, sustainable agriculture) to plant a sort of carbon bank using multiple layers of trees, shrubs, vines, and herbs to get the most out of every inch of earth. 

“Growing perennial plants (plants that live more than two or three years) around, above, and underneath other crops is the very best system for sequestering carbon that we have agriculturally,” he says. This is what we could be doing with our yards, instead of mowing grass. 

Effective Results: Offsetting An American’s Emissions
Toensmeier has around 300 species of perennials packed into one-tenth of an acre, and he says his yard is roughly “offsetting the emissions of a single American Adult every 10 years.” This would equate to 20.15 metric tons of CO2 each year. The median yard in America is 0.14 acres currently, so this density of growth could be very achievable in our own yards.

A significant increase occurs in relation to acreage. If his same yard “was an acre, it could offset the emissions of an American adult every single year,” Toensmeier states. However, “it is not an exact measurement,” he clarified. These calculations “are based on a rough estimation using guides to measure the soil carbon and soil organic matter.” 

The idea of using urban yards as a means to reduce greenhouse gas emissions is an exciting one, but if we can only roughly estimate our impact, is it viable? Enter the agroforestry wizards.

The U.S. Forest Service has done much to formulate accurate equations to calculate carbon sequestration down to the tree and the growing region. The Urban Tree Database and Allometric Equations report by Gregory McPherson, Natalie van Doorn, and Paula Peper, is an incredible resource. Within it, there are “365 sets of tree growth equations developed for the 171 distinct species,” along with methods for collecting data on the biomass of trees. There are equations for calculating carbon storage and a user guide on how to apply the equations to arrive at the amount of carbon stored over multiple years.

Okay, so calculating carbon sequestration accurately can be done, but how can it be done? 

James Cassidy, Soil Superstar
I asked James Cassidy, the Senior Soil Science and Sustainable Organic Agriculture Instructor at OSU, who was also described to me as the “soil superstar.” He said, “The math of the wood is related to the atomic mass of carbon.” In other words, using the atomic mass units of carbon and oxygen, we can calculate the molecular weight of carbon dioxide. It is a complicated series of calculations to arrive at an accurate value for carbon sequestration of a single tree, but you can go deep into algebraic ecstasy on it with the U.S. Department of Energy’s, Method for Calculating Carbon Sequestration by Trees in Urban and Suburban Settings, if you want to. 

Measuring carbon capture accurately is possible, in fact. But how does it work? How do plants capture the carbon? I am imagining a tree dressed like the Hamburglar running around grabbing giant Cs and Os and 2s out of the air and stuffing them in his big black sack, but somehow I don’t think that’s it.

How Plants Capture Carbon
Here’s how it works. Plants transfer carbon from the atmosphere to the rhizosphere (the soil) where carbon is stabilized and stored. While the plants are growing, they draw water and CO2 from the atmosphere through photosynthesis. The CO2 gets broken down into oxygen, which the plant releases back into the air, leaving carbon and water. These two products combine to form carbon sugars, or “liquid carbon,” which travels down the phloem (the vascular system, or veins of the plant) to the roots. The carbon then leaks out of the roots and into the soil, where if left undisturbed, it becomes stable and can be stored safely out of the atmosphere.

This process becomes most effective when cultivating plants that are fast growing, large, longer-lived, have large leaves, and wide crowns (the part of the plant that consists of the leaves and branches). Plants that meet all or most of these criteria trap the most carbon. A few of the many tree species that have these characteristics are yellow poplar, silver maple, oak, chestnut, dogwood, fir, spruce, and pine. 

One silver maple, for example, can sequester 25,000 pounds of CO2 in a 55-year period, according to the Center for Urban Forests and the U.S. Forest Service. That equates to 455 pounds of carbon dioxide pulled from the atmosphere each year. I ran these numbers by Greg McPherson, who is a Research Forester for the USDA Forest Service, who agreed that “455 pounds per year of CO2 sequestration for this type of large tree would be an accurate number.”

Creating the Perfect Yard
I am picturing my yard. How many silver maples could be planted on one-tenth of an acre? 

“A single tree with a 50 foot crown diameter has a crown area of 1,963 square feet,” says McPherson. A one-tenth acre yard equates to 4,356 square feet. If we use these numbers, we could plant two silver maples in a one-tenth acre yard, and capture 50,050 pounds of CO2 in 55 years. That’s nothing to shake a stick at, and according to the agroforestry system, this is not even reaching the maximum potential of carbon sequestration in our gardens. 

It is the multistrata approach that makes carbon capture gardens so successful. The upper canopy of trees offers just one layer of biomass. Planting successively lower tiers of perennials creates the formulaic density that traps the most carbon per acre. In other words, grow a whole bunch of perennial plants like dwarf fruit trees, edible shrubs, vines, and herbs around, in-between, and underneath those trees.

I asked Eric Toensmeier, why perennials? Why not just plant lots of annuals? 

He responded that “perennial plants have more above-ground biomass that stays year after year and grows, and half of that is carbon. The woody mass has a bunch of carbon in it, and that’s carbon that is removed from the atmosphere and held in place for the life of that plant. Annual crops don’t do that. They die at the end of the year, they totally break down, and most of the carbon goes back into the atmosphere.” 

Some Say It’s Just a Nice Theory
Some say that carbon farming is not a successful method for CO2 sequestration. In an article published by the Guardian, Gabrielle Chan reports that “carbon farming is a nice theory, but don’t get your hopes up.” 

A conservation cropping test plot in Australia formed by agronomist Dr. John Kirkegaard, and soil scientists Dr. Clive Kirkby and Dr. Mark Conyers showed that over 20 years, the carbon in the soil decreased by 30 percent, rather than increasing as predicted. 

However, it is important to point out that this test site used crop rotation, which means annual plants, not perennials. The soil is therefore disturbed more often, and carbon sequestration is disrupted and minimized. In addition, the multistrata approach of permaculture and agroforestry (trees, bushes, vines, herbs, etc.) was not examined. 

I asked Eric Toensmeier about this study, and he said, “a lot of people have taken that [study] to say there is no such thing as carbon sequestration, which is fundamentally not true.” 

“In annual cropping (growing various annual plants in a continuous rotation), no-till alone does not sequester carbon. It’s only when you add crop rotation and cover cropping, or add compost application, or add mulching, that the no-till system with annual cropping reaches its potential.”

There is an obvious need for further research on the viability of bio-sequestration utilizing agroforestry and permaculture farming practices on a global scale. And it needs to be on a global scale, Toensmeier says, to help solve the problem of global warming.

On an individual level, Toensmeier assured me, “we are so far from maximizing the potential of gardens in this country.” Utilizing this method of farming to sequester carbon “is important, and has to be seen in that light,” he said, “but there is no silver bullet. That’s not going to do it on its own. Every sector of civilization has to be redesigned and rebuilt on a fairly short timeline in order to do this, 10 to 15 years, and the whole landscape is one of those things we can use.”

I am feeling a bit optimistic at the moment, which is something I have not felt in a long time. We could be doing something right now in our own yards that can help mitigate global warming. It can cool our homes and produce food for our families. And if I’m going to be getting in that bucket anyway, at least I will have tried and will have something good to eat on my way.

By Blair Girard

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