Carbon Sequestration in an Urban Forest

Carbon Sequestration in an Urban Forest

Monica Szarvas, Evan Neims, Fletcher Klaykamp, and Hailey Ryneski

3/8/2015

Abstract:

Urban forests provide multiple environmental benefits. As urban areas expand, the role of urban vegetation in improving environmental quality will increase in importance. Mitigating climate change is imperative to human survival. Weaning off fossil fuel addiction is a slow process, that does not have a simple solution. Quantification of the sequestration rates of dominant tree species in our region can help us to mitigate climate change in the future. In this paper we will discuss our quantified results of carbon sequestration measurements. We will talk about the importance of continued partial mitigation of carbonic effluent. As well as the efforts its co benefits achieves.

As we have learned the last 8 weeks, the way many of us live life results in a lot of carbon waste.Anthropogenic climate change has caused a build-up of Carbon Dioxide and other greenhouse gasses (GHG) in our atmosphere. The accumulation of these GHG has raised the global temperature. With 50 to 70 percent of the population living in Washington state’scoastal areas [Gregory McPherson,Carbon Dioxide Reduction Through Urban Forestry,1999] the rise of sea level could have detrimental and direct effects on the Pacific Northwest.There is only one way to remove carbon from the atmosphere that we have yet discovered. That process is known as carbon sequestration. This is where trees absorb this carbon. Our group’s goal is to go out and take carbon sequestration readings from common native trees in the urban forest behind Evergreen’s F LOT.

Urban forestry and trees can reduce atmospheric CO2 inmanyways,including the restoration of nutrient lacking soils. Additionally,the responsible planning and planting of trees around a home can reduce its energy costs and emissions by up to 40% [David Nowak,A Short Course for Land Managers,2013] and through the process of Carbon sequestration. Treesuse photosynthesis to convert carbon dioxide (CO2) into sugar, cellulose and other carbon-containing carbohydrates that they use forbothfood and growth. Trees are unique in their ability to lock up large amounts of carbon in their wood, and continue to add carbon as they grow.

Hypothesis:

“Certainnativetree species can sequester more carbon than othernativespecies” This was our guiding question throughout the project. After researching the tree species on campus [Kevin M. McFarland,Campus Reserves Forest Species Composition Report,2007] we found that there were four dominant tree species on campus.Acer Macrophyllum(Big Leaf Maple),AlnusRubra(Red Alder),Pseudotsugamenziesii(Douglas Fir), andThujaplicata(Western Red Cedar). We found that one of these species,Pseudotsugamenziesii,was especially climate sensitive. “For the coastal variety of Douglas-fir, we found positive correlations of ring width with summer precipitation and temperature of the preceding winter, indicating that growth of coastal populations was limited by summer dryness and that photosynthesis in winter contributed to growth.” [PEI-YU CHE,Geographic Variation in Growth Response of Douglas-fir to Interannual Climate Variability and Projected Climate Change,2010] According to this if the Pacific Northwest becomes dryer our endangered Douglas-fir could die out,or travel to more suitable climates.

The alternative hypothesis was that “certainnon-nativetrees” sequester more carbon” since the dominant tree species in The Evergreen State College forest reserves were all native we did not get any data on Non-Native tree species.

Methods:

To incorporate the sequestration of urban trees in mitigating climate change, the rates of sequestration in tree species need to be quantified. The urban forest functions that appear to be most critical to environmental quality and associated regulations are tree effects on air, water, soil quality, and carbon sequestration.

Through our research we have discovered that there are many different methods to calculate the aboveground biomass of individual tree species. To find the appropriate equation for our research project we had to find a document that accounted for both conifers and deciduous trees,onethat calculated the biomass and the dry weight of above ground biomass.Our first step was to take the measurements required to complete the equations for finding out the sequester rate by tree. These measurements included the circumference of the trunk. For the tree I focused my research on,Acer Macrophyllum(Big Leaf Maple), themeasurements are as follows; Tree #1 Circumference at breast height is 11 feet 10.5 inches with a height of 128 feet and 8 inches. Tree #2 measured in with a circumference of 12 feet four inches, with a height of 114 feet and five inches. The third and final tree measurements came in with a circumference of three feet and five inches and a height of 79 feet and seven inches .These solutions were determined using a tape measurer. After figuring out the circumferences and heights, we put our measurements into the biomass equations and got our answers, which depended on what the species was and whether it was a softwood or a hardwood. After these details were established we converted the diameters from inches and feet into centimeters; the resulting numbers being: 362, 375, and 104 centimeters. We then entered these numbers it into the biomass equation.

BM= Exp(-1.9123+2.635 Ln(362))/2

BM=Exp(.4528 Ln(362))/2

BM=Exp(.4528*5.8916)/2

BM=445.563/2

BM=222.781 Kg

This is an example of the methodology used to solve one of the equations for one of the big leaf maples measured. We learned after collecting height data that it was not necessary, and quite variable. Therefore, we determined it did not play a role. Yet, it was an important part of time spent, so we found it necessary to include it.

As a group of four, we each had a specific native tree species that we would be focus on. We went together into The Evergreen State College forest reserve and measured three of each species to get an average of Diameter at breast height (dbh).

To calculate current carbon storage and annual carbon sequestration, biomass for each measured tree is calculated using equations from the literature [Jennifer Jenkins,Comprehensive Database of Diameter-based Biomass Regressions for North American Tree Species,2003]. Equations that predict above-ground biomass were converted to pounds from kilograms. Total tree dry weight biomass was converted to total stored carbon by dividing the weight by 0.5. Each species group has their own unique parameters, so we attuned our equations as such.

Results:

Urban forests can directly and indirectly affect the air quality of a region. “In the US, urban forests are estimated to remove about 71 1,000 metric tons ($3.8 billion value) of air pollution per year” [David Nowak,Institutionalizing urban forestry as a "biotechnology" to improve environmental quality,2006] by sequestering atmospheric CO2 trees are mitigating climate change and improving our air quality. Focusing on the four dominant tree species on campus,Acer Macrophyllum(Big Leaf Maple)AlnusRubra(Red Alder)Pseudotsugamenziesii(Douglas Fir) andThujaplicata(Western Red Cedar) research shows that the species sequestering the most CO2 areAcer MacrophyllumandPseudotsugamenziesii.

The above graph shows the sequestration rates of the species in its lifetime. The information was gained through research of the individual tree species, and the measuring of the trees in The Evergreen State Colleges forest reserve.AlnusRubrahas a significantly shorter life span than the other trees, its lifespan is on average 60 years.However, itsequesters CO2 annually at around the same rate as the other four native species we studied.Acer Macrophyllumsequesters the most CO2 compared to the three other species of tree. Bigleaf Maple has an average lifespan of 180-200 years. A possible theory for the higher sequestration rate is thatAcer Macrophyllumis a deciduous tree; when a deciduous tree comes out of dormancy in the spring time it has does a sort of “resource rush” and begins to photosynthesis at a faster rate than that of a conifer that is photosynthesizing all year. Additional research could help us get a larger average for Acer Macrophyllumto see if it really is sequestering the largest amount of CO2.Pseudotsugamenziesiihas an average lifespan of 500 years, with its long life span it learns to sequester carbon more efficiently as it gets older.Thujaplicataa conifer with an average lifespan of 220 years.Historically referred to as the “tree of life” by the Pacific Northwest Native Americans.Researched showed that the Western Red Cedar can sequester about 70,000 lbs of CO2 in its lifetime.

Discussion:

According to the researchAcer MacrophyllumandPseudotsugamenziesiisequester the most CO2. Looking to native trees to mitigate climate change in our region could be problematic. Recent studies show thatPseudotsugamenziesiiis an endangered tree species that may not be around in the next 50 years [Soo-Hyung Kim, Assessing the Impacts of Climate Change on Urban Forests in the Puget Sound region: Climate Suitability Analysis for Tree Species, 2012] Monitoring our Urban Forests sequestration rates is an excellent start in using trees to clean up our atmosphere. In the urban forests of cities however, climate change will very likely increase several stressors on trees - making it even more important that we manage the fundamentals of urban forest health such as soil volume, soil quality and soil oxygen availability, as well as species diversity so we can increase the biodiversity of the urban forest overall, rather than attempting to select the “right” species for predicted future conditions, the plasticity of a species, or its ability to thrive in a wide variety of conditions, may be more important in selection for resilience than any single variable, such as drought tolerance or temperature range, alone.

Significance:

These findings are significant because we have yet to find a way of removing carbon dioxide from the air in another manner. Urban forests are not only a way to mitigate anthropogenic carbon dioxide, they also play an important role in energy conservation and soil quality. Planting more trees and maintaining healthy urban forests is a very important part of partially mitigating fossil fuel effects until we can really start to move over to renewable energies. They are they are the only way we know how to remove the pollutants we are creating, besides not emitting them at all.The Evergreen State College is trying to become carbon neutral. We believe harboring an urban forest is an important part of that goal.

Continued research on this topic might include answering questions like; How much carbon does The Evergreen State College urban forest actually counter? What is the real carbon footprint of Evergreen if we include that in our emissions analysis? We could also look into non-native higher carbon sequestering trees and the ways that urban sidewalk trees affect people and their willingness to walk and spend more. We could look more in-depth at individual species, where they thrive, what soil do they prefer, what service could they provide in an urban setting or as a street tree.

Acknowledgements

This project was made possible by the continuous support of our program faculty, E.J Zita and Nancy Koppelman. Zita was with us in every step of our research, helping it grow and expand, and challenging us to think of new aspects to our project. Nancy Koppelman aided us in writing workshops, without which this paper couldn't have been articulated.

Kevin M. McFarland, Campus Reserves Forest Species Composition Report, 2007

This document kick-started our research it pointed us in direction we needed to go and told us what trees were dominant, so that we could research the species.

PEI-YU CHE, Geographic Variation in Growth Response of Douglas-fir to Interannual Climate Variability and Projected Climate Change, 2010

This is one of two documents that I read about Douglas-fir climate sensitivity.

Jennifer Jenkins, Comprehensive Database of Diameter-based Biomass Regressions for North American Tree Species, 2003

This document had the equation that we used to get the dry weight above ground biomass for our tree species.

Soo-Hyung Kim, Assessing the Impacts of Climate Change on Urban Forests in the Puget Sound region: Climate Suitability Analysis for Tree Species, 2012

This paper was about how climate change would affect native tree species in the Pacific Northwest.

Forest Sequestration Controversy: Old-growth vs Young-growth Forests as Viable Carbon Offsets

This is a small article about young trees and old growth trees and thier sequestration rates. Which one is better? The article is inconclusive.

David Nowak, Institutionalizing urban forestry as a "biotechnology" to improve environmental quality, 2006

The benefits of an Urban forest as a biotechnology, meaning that trees benefits could be more than just there sequestration abilities.

Joe Roush, The City of Olympia Master Street Tree Plan, 2011

This is a comprehensive document of all the current street trees in olympia, as well as the maintenance for them.