In recent years the IMA has made a commitment to the Indianapolis community to become more conscientious stewards of the environment in its pursuit of fulfilling the museum’s mission. This has been a worthy challenge for an institution to take on within the confines of the museum itself, but we also have the unique position of having 152 acres of gardens and woodland that give us an advantage over many urban institutions when measuring our carbon footprint. In an effort to evaluate that advantage, we turned to a software analysis tool created by the USDA Forest Service called i-Tree.
The intention of i-Tree is to allow communities and other users to assess their current urban forest cover, create awareness and educational opportunities, and guide application for better management of those trees. It has frequently been applied on a city-wide scale, but can also analyze an entire state’s urban forest, or a small, local city park. The results are based on field data collected from random plots, accounting for tree species, height, trunk diameter, and canopy characteristics. The data is then entered into the Urban Forest Effects (UFORE) analysis model, which calculates the amount of air pollution removed, carbon sequestered and stored by the trees, and sustained economic benefits.
To elaborate on the terminology of carbon sequestration and storage, a brief review of plant photosynthesis may be helpful. Photosynthesis is the process of converting light energy to chemical energy in the form of sugar (glucose). Carbon dioxide (CO2) and water (H2O) molecules are broken down with energy from the sun into glucose (C6H12O6), a usable energy form, and oxygen (O2), which, lucky for us, is expelled into the environment as a waste product.
Eventually, that glucose can be reorganized into different forms: sucrose, starch and cellulose. Each of these sugars is made of a different 6-carbon compound, which are used as sources for plant energy, or stored as organic compounds to develop plant growth and the structural form of the plant (i.e. the inner wood of a tree). Think of these terms when discussing carbon sequestration and storage, where you can associate sequestration with removing carbon from the air for the process of photosynthesis, and associate storage with the amount of carbon that has been accumulated in the size development of the tree. This is important, because if the tree were to die, all that stored carbon would be released back into the air or soil as the tree decomposes.
The results of measuring carbon sequestration and storage have more meaning when you can understand, in part, how they fit into the plant’s life cycle. Now that you know some of the conditions and terminology, you’re ready to hear what we found about our own, IMA urban forest!
In evaluating the entire IMA campus, including 100 Acres and the Oldfields estate, we found that an estimated total of 750 tons of carbon is sequestered annually by our tree cover, and over 10 tons of pollutants are removed from the air. Assigning an economic value to that number means that these trees are naturally filtering the air for what would annually amount to a savings of about $47,500 associated with health costs and reduction controls. It is interesting to note that the amount of carbon sequestered by the Oldfields estate’s mature tree cover alone is enough to counteract the annual carbon emissions from 300 automobiles, which theoretically means that we balance out our yearly carbon emissions from all staff vehicles. That doesn’t even take into account the amount being sequestered by the remaining tree canopy. Of course, we could never achieve zero-output on emissions using vegetation alone, but it’s encouraging to realize the impact of what currently exists. Considering that the museum has reduced building emissions by 12,500 tons over the past five years (about 2,500 tons/year), it is clear that a significant means for balancing emissions comes not from enacting curative measures, but applying preventative measures and reducing output in the first place. Perhaps the next step would be to measure the total output of carbon and pollutants from the campus buildings for a scale comparison.
In terms of carbon storage, there are approximately 30,000 tons of carbon currently stored in tree mass at the IMA. The amount stored annually varies according to tree type, maturity, size and health of an individual tree, but taking into account that the process of decomposition is much faster than that of building and accumulating plant matter, it is wise to consider the amount of carbon that would be emitted back into the atmosphere if we were to lose or remove the current tree canopy. From one perspective it would seem that fallen trees themselves are contributors to the global concern for increased levels of carbon in the atmosphere, but bear in mind that a dead tree decomposing on the forest floor is a natural part of its life cycle and ecosystem. It provides habitat for wildlife, and the decaying tree releases carbon into the soil which supplies nutrients for the live vegetation around it, food for microbes and insects, and contributes to good soil structure. There are many such trees in 100 Acres.
What is of greater concern is a lack of balance, where trees are removed for the development of buildings and other such construction that will output large amounts of carbon, gases and particulate matter. Where there is no consideration for counterbalancing these outputs is where the danger lies. Nature is in a constant process of trying to maintain equilibrium in the environment, and with tools such as i-Tree to aid our understanding of where we currently stand, we can make educated decisions that will support that process.