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’s coastal 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 in many ways, 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. Trees use
photosynthesis to convert carbon dioxide (CO2) into sugar, cellulose and other carboncontaining carbohydrates that they use for both food 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:
“Certain native tree species can sequester more carbon than other native species” 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), Alnus
Rubra (Red Alder), Pseudotsuga menziesii (Douglas Fir), and Thuja plicata (Western Red Cedar).
We found that one of these species, Pseudotsuga menziesii, 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 “certain non-native trees” 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, one that 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),
the measurements 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) Alnus Rubra (Red Alder) Pseudotsuga
menziesii (Douglas Fir) andThuja plicata (Western Red Cedar) research shows that the species
sequestering the most CO2 are Acer Macrophyllum and Pseudotsuga menziesii.
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. Alnus Rubra has a significantly shorter
life span than the other trees, its lifespan is on average 60 years. However, it sequesters CO2
annually at around the same rate as the other four native species we studied. Acer
Macrophyllum sequesters 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 that Acer Macrophyllum is 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 Macrophyllum to see if it really is sequestering the
largest amount of CO2. Pseudotsuga menziesii has an average lifespan of 500 years, with its
long life span it learns to sequester carbon more efficiently as it gets older. Thuja plicata a
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 research Acer Macrophyllum and Pseudotsuga menziesii sequester the
most CO2. Looking to native trees to mitigate climate change in our region could be
problematic. Recent studies show that Pseudotsuga menziesii is 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 nonnative 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
http://oldvsyounggrowthforestasoffset.weebly.com/why-is-it-controversial.html
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.