Yale University School of Forestry & Environmental Studies
FES519B - Methods of Ecosystem Analysis 1998
 ABOVE-GROUND 
BIOMASS 
and
NUTRIENT ESTIMATES
at a
MIXED DECIDUOUS 
and 
HEMLOCK-HARDWOOD FOREST
TOTOKET MOUNTAIN, 
NORTH BRANFORD, CT
1998
 
Photo credit: http://bluehen.ags.udel.edu/gopher-data2
/.conifers/.descriptions/t_canadensis.html
 


About this Web page
        The data presented below are the result of a term project for Professor Tom Siccama's FES 519b: Methods of Ecosystem Analysis class at the Yale University School of Forestry and Environmental Studies.  Field sampling was done from January-March 1998 at Totoket Mountain near North Branford, CT.  We are indebted to the Regional Water Authority for providing access to the site.

        The results are based on field measurements of 101 plots, each 6 m x 30 m, arranged along two transects.  Plots were established to study the composition and structure of the 70-100 year old mixed deciduous and hemlock/hardwood forest at Totoket Mountain (click here to get more information on the forest composition and structure).  The "Uphill" transect, plots 1-51, ran in a north-west direction, and ranged in elevation from roughly 290 ft to 510 ft above sea level.  The "Countour" transect, plots 52-101, ran in a  north-east direction, and stayed as near as possible the 350 ft contour line.  The "Uphill" transect is considered more xeric, the "Contour" transect is more mesic.

         Please note: Biomass results are expressed in Mg / ha, or metric tons per hectare.  1 Mg = 1,000 kg = 1,000,000 g


What's Below
        On this page, you'll find the following information about the above-ground live tree biomass and above-ground nutrient estimates at Totoket Mountain, CT:
How are biomass estimates computed?

     Allometry equations, usually in one of two forms,
               biomass = a x dbh b
               biomass = a + b log (dbh)
    allow a reasonable estimation of the above-ground biomass to be made, based solely on knowledge of tree species and tree diameter (the equation coefficients, a and b, are different for different species).

       The following figure illustrates how biomass estimates vary by species of the same diameter at breast height. One reason that different species trees of the same diameter have different amounts of above-ground biomass is that different species have different architectures.  Another reason is that the wood of some species is much more dense than that of other species: for example, hemlock has a wood density that is roughly one-half that of most hardwood species.
 

       Based on data collected in the field at Totoket Mountain, we applied (where possible) the species-specific allometry equations contained in Tritton and Hornbeck's (1982) "Biomass Equations for Major Tree Species of the Northeast" (USDA Forest Service, Northeastern Forest Experiment Station, GTR NE-69).   Generally, Brenneman et al.'s (1978) equations for West Virginia hardwoods were applied.  In the cases where Tritton and Hornbeck did not give an equation for the species in question, then we applied the Monk et al. (1970) "General Hardwoods" equation, or the Monteith (1979) "General Softwoods" (see Tritton and Hornbeck (1982) for Monk and Monteith sources).

         The numbers presented below are estimates: the validity of applying equations derived in West Viriginia to a site in Connecticut can be debated until the cows come home.

         For comparative purposes, 1997 data from the 80 year old forest at Watershed 6, Hubbard Brook, NH, are provided where appropriate.


Biomass Estimates: 1993 vs. 1998
 
Above-ground live tree biomass, Mg/ ha
1993
1998
Net %
Change
Totoket Mountain
Uphill plots (#1-51) (xeric)
142
148
+ 5%
Contour plots (#51-101) (mesic)
148
162
+ 9%
Total
145
155
+ 7%
 a
 
1997
Hubbard Brook 
195
 
 

Based on the above, aboveground live biomass at Totoket Mountain increased at approximately 2,000 kg / ha annually over the five-year period 1993-1998.
 


Biomass Estimates: Major Tree Species
 
Above-ground live tree biomass, Mg/ ha
1993
1998
Net % 
Change
% 1993 
Total
% 1998
Total
Totoket Mountain
Acer saccharum 
34
 37
+6%
23%
24%
Quercus alba
35
 36
+1%
24%
23%
Carya sp.
 14
 15
+4%
10%
10%
Quercus rubra
14
 13
-6%
10%
8%
Fraxinus americana
6
8
+34%
4%
5%
 a
Hubbard Brook 
 
 1997
% 1997
Total
Acer saccharum
 
71
36%
Fagus grandifolia
 
62
32%
Betula lenta
 
40
21%
 


QA / QC of Biomass Estimates

        We wondered "does it matter whether we use species-specific allometric equations? Or do we get a pretty good estimate of total biomass by just using a general hardwoods equation?"
 
        We compared our "best estimate" of total biomass (using species-specific equations) with  biomass calculated using

        We found that the Monk equation comes remarkably close to the "best estimate" of total biomass:
 
Above-ground live tree biomass, Mg/ ha
1993
1998
Species-specific equations
144
155
Harris et al. 
115 
122
Monk et al. 
147 
156
Brenneman et al. 
177
188
 


Nutrient Analysis
        We estimated the total calcium and magnesium content of the aboveground biomass by applying plant tissue nutrient concentrations measured by Hunter and Siccama (1996) at the Quinnipiac River and by a previous FES 519b class at Sea Hill.  For each tree species we used an average of the available data.  For an entire tree, the amount of a given nutrient is a function of four factors:         The fourth factor is somewhat problematic.  At Hubbard Brook, bole bark accounts for 4.0% of tree biomass for beech, 6.4% for yellow birch, and 7.8% for sugar maple (average 6.1% for the three species).  This does not take into account the amount of bark on the branches, however, so we did our best to adjust for this.  We believe that there is a higher percentage of bark in branches than in the bole, and therefore we thought it reasonable to add an additional four percentage points to the bole bark figures to arrive at a very approximate bark biomass percentage for the entire tree.  Therefore, we used 10% as a rough estimate of the total bark biomass percentage for all tree species.
 
         Based on this estimate, we calculate the following nutrient totals in the aboveground live biomass at Totoket Mountain:
 
 
kg / ha
1993
1998
Net % 
Change
Totoket Mountain
Calcium
558
583
+4%
Magnesium
34
37
+8%
a  
 
Hubbard Brook
1997
Calcium
551
Magnesium
48
 
       Nutrient levels at Hubbard Brook appear to be of the same order of magnitude as at Totoket Mountain.  Magnesium levels are quite a bit higher at Hubbard Brook, whereas Calcium levels are only a small amount higher at Totoket Mountain.
 
        As mentioned above, these estimates are sensitive to the bark biomass percentage assumed.  The following two graphs show how estimated nutrient totals change as the bark biomass percentage is increased or decreased.


 
 


Biomass Modeling
 
        As an experiment, we decided to try define a model to estimate the above-ground live tree biomass at Totoket Mountain five years from now (2003).   First, we checked the model using 1993 data to estimate 1998 data: the model performed quite well when the totals were compared with what we estimated based on this year's field measurements.  We then ran the model using the actual 1998 data to forecast 2003 data. We will leave it to a future FES 519b to check the validity of  these results!

        In order for the model to work, we had to make a number of assumptions above mortality, tree growth, and regeneration.  These assumptions are as follows:

 
Above-ground live tree biomass, Mg/ ha
Established Trees
Ingrowth
Total Tree Biomass
Run 1
158
0.6 
159
Run 2
157
0.8 
158
Run 3
158
0.7
158
Run 4
159
0.7 
160
Run 5
155
0.9 
156
Average
157
0.8 
158
± std dev
2
0.1 
2
 
The average 1998 biomass predicted by the model is 158 Mg / ha, which is quite close to the estimated biomass of 155 Mg / ha.
   
Above-ground live tree biomass, Mg/ ha
Established Trees
Ingrowth
Total Tree Biomass
Run 1
165
0.6 
166
Run 2
167
0.4 
 167 
Run 3
167 
0.5 
168
Run 4
170
0.8 
171
Run 5
163
0.6
164
Average
166 
0.6
 167 
± std dev
0.1 
 2 
 
The average 2003 biomass predicted by the model is 167 Mg / ha.  Hopefully someone will re-survey our transects in five years to see how close the model is to being right!
 
       Model Sensitivity

        The model is quite sensitive to the mortality rate and annual growth rate assumed.  On the other hand, the amount of ingrowth is so small as to be more or less insignificant.

        The following figures compare the effect of changes in the level of annual mortality and annual growth rate on the forecasted biomass.


 


Species-by-species Biomass and Nutrient Data

        Click here to see the table of biomass and nutrient data.
          Click here to see the species list.


Download the Biomass Modeling Spreadsheet

        You can download our biomass model as a Microsoft Excel spreadsheet.  It may take some time.  Click here to download.



 
Biomass estimates brought to you by: 
        Nancy Fresco 
        Andrew Richardson 
        Yale School of Forestry and Environmental Studies 

With thanks to: 
        New Haven Regional Water Authority 
        Tom Siccama 
        Dan Vogt 
        and the Plantheads (Phytosociology Crew)