Terrestrial Succession,
Biomass Per Unit Area and Carbon Sequestration
The amount of plant biomass per unit area on a tract of land can provide information about the age of the tract
of land and its capacity to sequester CO2 from the atmosphere (which counteracts man-made greenhouse
gases). The "succession" age of a tract of land indicates if it is old growth (rare primeval forests ) or has
developed its plant community more recently. Forested tracts of land which developed on lands which were
farmlands abandoned in the late 1800's or 1900's are termed secondary growth. Tracts of lands that were clear
cut for timber and subsequently developed forests are also termed secondary growth.
Succession (Fig. 1) is the change in plant and animal communities that occurs after new land is created or after a
major disturbance. Landslides and floods can destroy plant communities and bury them in soils and rocks
resulting in barren land. Volcanoes also create barren ground by means of laval flows and explosive events.
Succession beginning with barren land is termed "Primary Succession." Succession beginning after a disturbance
such as a forest fire is termed "Secondary Succession." The succession that occurs after agricultural land is
abandoned and after clear cutting timber is "Secondary." Secondary succession takes less time than primary
succession because the soil base or foundation exists. Primary succession begins with early colonizing species
such as lichens, grasses and short lived annuals. Soil builds up slowly from accumulated detritus (dead organic
matter) and minerals. As the soil gets deeper larger plants can take root from seeds brought in by wind, rain and
animals. Succession stages are normally described by the plant communities which develop on the land over
time. Of course animal communities also change. The final plant community is termed the "climax community."
The climax community will be determined by the biome in which the tract undergoing succession is in. A
succession event in central Canada would produce a Boreal Forest. A succession event in central Eastern United
States would result in a Temperate Deciduous Forest.
Figure 1. Succession from barren soil to hardwood climax forest over 100 or more years.
Annual production (kg biomass/unit area/year) increases rapidly during early succession years then levels off
after 100-150 years (Figure 4). Once a tract of forest is about 200 years old it capacity to sequester CO2 is fairly
constant. The biomass per unit area increases over the first hundred to one hundred fifty years then levels of at
about 400 Metric tons per hectare (written as 400 Mg/ha; equals 400,000 kg/ha or 40 kg/m2).
Figure 2. Succesional age of tree stand and accumulated biomass in metric tons per hectare (Mg/ha).
Smithsonian Environmental Research Center. (www.serc.si.edu/labs/forest_ecology/production.aspx)
Forested tracts of land have value on the world carbon credit market. The value of a tract of land in terms of
carbon credit1 ($/ha/year) is related to the biomass/ha and its location (biome) since forests closer to equator
can sequester more CO2 per year. A tract of land sold for its carbon credit value is placed into "long-term
reserve" status. The land is more-or-less long term leased. The concept is simple. A large tract of land is left
alone or subject to lesser timber harvest and allowed to remove CO2 from the atmosphere by means of
photosynthesis from is photo-autotrophs (plants). The land can still be used recreationally. Many countries have
adopted the concept of carbon credits. An industrial producer of CO2 can pay fines, reduce CO2 outputs or
purchase carbon credits and allow mother nature to reduce CO2. The concept of carbon credits recognizes that
truth that CO2 is a global problem and can be solved globally. sequestration of CO2 can be accomplished at a
distant location. Depending upon the current cost of carbon credits (expressed as kg CO2 e) an acre of land can
yield $5 or more per acre per year ($13 per ha per year). Large tracts of land can generate enough money to
pay for taxes. If the value of CO2e increases carbon credits might even exceed the value of timber.
The goals of this lab are to:
1) Estimate the mean biomass per unit area (Mg/ha ) of trees from field data and spreadsheet. (Steps 1-3)
2) Estimate the age of a forested tract of land based upon its biomass density.
3) Plot a Histogram of the size distribution of the sampled trees. (from pooled data on field sheets)
4) Calculate the value of a tract of land in terms of its value for carbon credits (40 ha times current $/ha)
5) Estimate the capacity of a tract of land to sequester the CO2 produced by a typical university student’s
annual driving. (Steps 4,5,6,7)
Your instructor will identify one or more locations for you measurements by marking with a flag.
All trees with DBH values > 10 cm within the plot radius (e.g., 8-m) will be measured individually (Fig 3).
Trees with DBH’s less than 10 cm (circumference < 31 cm) will be enumerated.
Your instructor will tell you what radius to measure (e.g., 8 meters).
A tree’s diameter at breast height2 (measure about 4 feet above ground) will be measured to nearest centimeter
(cm). A special tape measure will be used.
Figure 3. All trees in a specified radius will be measured.
The tape measure is wrapped around the tree (Fig. 4) and the “special side” of the tape measure is read. The
special side makes the mathematical conversion of circumference to diameter. For this exercise you will not be
recording species of tree and you will use a generalized equation in your computations which works well for
typical hardwood species of trees.
Figure 4. Diameter at Breast Height (DBH) is recorded in cm by wrapping a special converting tape measure around tree
at about four feet off the ground.
Dry Weight to Carbon and Carbon to CO2
Plants and algae sequester CO2 from the air and water CO2 is in equilibrium between air and water) by
incorporating CO2 into sugars in the Calvin Cycle of Photosynthesis. CO2 is sequestered mostly as cellulose (and
other structural carbohydrates which are polymers of sugar) which we commonly call “wood.”
Q -Question: What is the AVERAGE biomass per m ?
2
Steps 1 to 3 are computed in the spreadsheet linked on syllabus.
Step 1. Diameter at Breast Height (DBH) will be converted to dry weight in kilograms using the equation
(Uses Formula and Coefficients from Table 4 in "National Scale Biomass Estimators For United States Tree
Species. Jenkins, et al. Forest Science 49(1) 2003)
Dry kilograms Biomass mixed hardwood = EXP (β0 + β1 ln dbhcm)
Where β0 = -2.4800,,and β1= 2.4835
Step 2. After the dry weight of all the trees are added for your 8-m radius plot, compute the weight (kg) per
square meter by dividing by 200.96 the area of your plot (e.g., 8-m radius plot has area of 200.96 m2; 3.14 x 82)
Step 3: Next multiply by 10,000 to arrive at your estimate of dry kg per hectare (note: there are 10,000 m2 in a
hectare).
Example: Suppose mean is 35 dry kg /m2
Then the biomass is 350,000 dry kg/ha.or 350 Mg/ha
Q -Question: What is the estimated age of this tract of land based upon its AVERAGE biomass per m ?
2
If the average biomass is 350 Mg/ha (350,000 kg/ha), the tract of land is about 135 years old using Figure 5.
Figure 5 . Smithsonian Environmental Research Center. (www.serc.si.edu/labs/forest_ecology/production.aspx)
Q –Question What is the size distribution of trees? Use the data from all groups to plot a Histogram which
shows the frequency (Y-axis) as function of the different tree sizes (X-axis) (measured as DBH in cm). An
example Histogram is shown below.
Figure 6. Example histogram.
Q -Question: What is the annual value of the Carbon Credits for the 40-ha tract based upon current market
value ($10-20/ha) (note: 1 acre = 0.4045 ha)
Q -Question: What is the annual capacity for the tract of land to sequesterCO ? (its CO e)
2
2
(Convert dry biomass to weight of Carbon, then CO2),then divide by years to get annual CO2 sequestration rate)
USE MEAN FROM POOLED CLASS DATA FROM STEP 3 (350,000 dry kg/ha in example).
Step 4. Convert MEAN dry kg trees/ha to MEAN kg carbon/ha equivalent by multiplying by 0.45.
(note: Carbon is 45% of the weight of a sugar monomer C6H12O6)
Example: 350,000 dry kg/ha x 0.45 = 157,500 kg C/ha
Step 5. Convert MEAN kg carbon/ha to MEAN kg CO2 /ha equivalent by multiplying by 1.65
(note: a CO2 is 1.65 times as heavy as just a carbon atom).
Example: 157,500 kg C/ha x 1.65 =͌260,000 kg CO2/ha
Step 6a. Since the tract of land is 40 hectares, multiply MEAN kg CO2 /ha by 40 ha to estimate TOTAL kg CO2
sequestered in this tract of land.
Example:260,000 kg CO2/ha x 40 ha = 10,400,000kg CO2
Step 6b. Express as Metric Tons of CO2. A metric ton is 1,000 kg. So divide TOTAL kg CO2 by 1,000.
Example: 10,400,000 kg CO2 ÷ 1,000 = 10,400 metric tons of CO2 has been sequestered by the tract of
land.
This is the CO2 e (CO2 equivalent) expressed as metric tons.
Step 7. It has taken that many years to store the amount of CO2 estimated in Step 6b. Divide Metric tons of CO2
by years in order to estimate annual metric tons CO2 e sequestered by the tract of land.
Example: 10,400 Metric tons of CO2 ÷ 60 years = 173 metric tons of CO2/year
Q -Question: What is capacity of the tract of land to sequester CO produced by student driving?
2
Trees CO2, Gasoline & Cars
A gallon of gasoline produces 0.008887 metric tons of CO2.(US EPA)
Suppose a typical Furman Student drives 1,000 miles per year. Then the student body (@ 3000 students) drives
3,000,000 miles per year. If the cars driven by students average 20 miles per gallon then they use150,000 gallons
of gas per year.
150,000 gallons per year x 0.008887 metric tons CO2 per gallon = 1,333 metric tons of CO2 per year.
This means that the tract of land sequesters the CO2 produced by driving for about 13% of the Furman Student
body (this is based upon a mean biomass of 350,000 kg/ha from Step 3)
APPENDIX
Appendix Figure 1. The 40 hectare tract of land adjacent to Furman University Campus.
References
Jennifer C. Jenkins, David C. Chojnacky, Linda S. Heath, and Richard A. Birdsey.2003. National-Scale Biomass
Estimators for United States Tree Species Forest Science 49(1):12-35. 2003
1
http://en.wikipedia.org/wiki/Carbon_credit
2
http://en.wikipedia.org/wiki/Diameter_at_breast_height
http://esa21.kennesaw.edu/activities/trees-carbon/trees-carbon.pdf; "Above ground biomass and nitrogen
allocation of ten deciduous southern Appalachian tree species", Martin, Kloeppel, Schaefer, Kimbler, and
McNulty, Can J. For. Res. 28: 1648-1659 (1998).
3
DBH
(cm)
Table/Plot
DBH
(cm)
Table/Plot
Table/Plot
DATE:
Trees with DBH 10 cm or greater (Circumference > 31 cm) are Individually Measured.
DBH
(cm)
Trees with DBH values < 10 cm (Circumferences < 31 cm) Are Enumerated (counted) (use IIII )
TOTAL NUMBER < 10 cm =
Assume Average of 5 cm and Average Wt of 4.1 kg for these small trees; Multiply the number
of small trees x 4.1 kg to arrive at their combined estimated weight in kg =
(transfer this number to spreadsheet)