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Forest Ecology and Silvics

Laboratory 1

Analysis of the Phytosociological Field Data

Compiled by:______

______

Name of Sample Area:______

Laboratory Section:______

Date:______

Laboratory 1 - Analysis of the Phytosociological Field Data

Calculation of Importance Values

General Information

Having completed the data collection, the information must be summarized into useable format. This involves a series of calculations that will be outlined in this handout. As with any calculations, care must be taken to ensure that the work is performed correctly. To assist you in this undertaking, the summary sheets have been designed to include all the necessary steps and totals so that you will be able to continually cross-check your addition, and to make the necessary corrections before they are used in further calculations. (Note - Please refer to your first year mensuration lab notes for the correct procedures for rounding and carrying decimal places.)

Once all calculations are completed, an Importance Value will be determined for each of the three strata. The Importance Value for the tree layer will be determined by totaling the Relative Density, the Relative Dominance, and the Relative Frequency. Since all “Relative” values are out of 100, the Importance Value for the tree layer will be out of 300. This differs slightly from the Importance Value for the shrub and herb/moss layers. The Importance Value for these two layers is out of 200 as only the Relative Dominance and Relative Frequency are considered. On the last page of the tally sheets for this lab, the Importance Values, by species, for the tree, shrub, and herb/moss strata will be listed and totaled to produce an overall Importance Value that will be used to describe the community as a whole. It is very important, however, to be well aware of the components of the total Importance Value and to use that knowledge to describe the structure of the community in your upcoming “Stand Description” assignment.

The following instructions include calculation examples (Table 2) based on the numbers listed in Table 1 (Sample field data for Tree Strata). You will be able to follow along step by step, as outlined, and see how the calculations were performed by referring to the data sheets.

The data that you will be using in Lab 1 is a composite of that collected during field school. Information from several tally sheets has been combined in order to produce a working document. You will need your notes from Field School in order to recall details about the topography, geomorphology, the soils and the stand condition for the Forest Community Description Lab (Lab 2).

Part 1 - Tree Stratum

Example calculations for Relative Density, Frequency and Dominance are all based on the data provided for jack pine in Table 1.

1. Determine the average density (number of trees per hectare) for the community as follows:

  • add the distances measured to each tree in each quarter to obtain the Total Distance.
  • count the number of trees that were recorded in all of the quarters (No. of Trees).
  • divide the Total Distance by the No. of Trees to determine the Mean Distance. Since one hectare equals 10,000 m2, dividing 10,000 by the (Mean Distance in metres)2 will provide you with the number of trees per hectare, or density, for your plots.
  • the following example is based on the sample tally sheets

Total distance = 98.6 mNo. of Trees = 40

Mean distance = 98.6  40

= 2.5 m

No. of trees per hectare = 10,000  (2.5)2

= 1600 trees per hectare

2. Determine the Relative Density of all species in the tree stratum.

  • list each tree species encountered under “Species” (column C1).
  • count the number of individuals for each species; list the count under “No. in Quarters” (column C2).
  • count the total number of trees in all quarters, this should be the same as the “No. of Trees” per sample from step 1. This number will fill the column “Total in Quarters” (C3), and will be the same for all species.
  • calculate Species Density, (this expresses the number of times that trees of a species occurred in the sample):

Frequency = (No. in Quarters  Total in Quarters) or (C2  C3)

= 2  40 (for jack pine)= 0.05

  • transfer the No. of Trees per hectare value (from step 1) to column C5 “Mean Density”. This number will fill the column, and will be the same for all species.
  • calculate the No. of Trees per hectare by species(column C6):

No. of trees per hectare (by species)

= Frequency x Mean Density or (C4 x C5).

= .05 x 1600 (for jack pine)= 80 jack pine per hectare

  • total the number of trees per hectare column (C6), it should sum to the Mean Density value. This total is listed in the appropriate “Total” box at the bottom of column C6.
  • calculate the Relative Density (remember that relative values are always out of 100):

Relative Density = (No. of trees per hectare  Mean Density) x 100
or (C6  C5) x 100) = (80  1600) x 100= 5.0

  • total the Relative Density values to confirm that they do indeed, sum to 100. If the total is not 100, then review and/or redo the preceding calculations to find, and correct, the error. (Use whole numbers and follow the rounding rules to eliminate more than one decimal place.)

3. Determine the Relative Frequency of all species in the tree stratum.

  • Relative Frequency is calculated in much the same way as was Relative Density. The main difference between Frequency (and Relative Frequency ) and Density (and Relative Density ) is that frequency looks at only presence or absence, while density deals with actual numbers of individuals.
  • List each tree species encountered under “Species”.
  • count the number of points (not individuals or quarters ) in which each species occurs. List this under “No. of Points”.
  • count the number of points tallied. List this number in the “Total Points” column. (Note - it isn't always 10!)
  • calculate the Frequency:

Frequency = (No. of Points  Total Points) x 100

= (2  10) x 100= 20

  • sum the Frequency column and list the total in the appropriate Total box.

  • calculate Relative Frequency (remember that relative values are always out of 100):

Relative Frequency
= Frequency (of a species)  Total Frequency (of all species)
= (20  210) x 100= 9.5

  • sum all the Relative Frequency values. These should total 100. If this is not the total, then there has been an error in the calculations. Review and redo, if necessary, the preceding steps until this total equals 100.

4. Determine Dominance by species, using diameter and basal area.

  • list each individual tree by species and corresponding diameter (each species is listed in a separate Dominance column).
  • calculate the basal area per tree (in dm2) by squaring the tree’s diameter (in cm) and multiplying by the constant 0.007854. The resulting value is the basal area expressed in m2:

Basal area = (diameter in cm)2 x 0.007854

= (34) 2 x 0.00007854

= 9.0 dm2 (for a tree with diameter 34 cm)

  • basal area must be calculated for each of the trees tallied
  • sum the basal area by species to determine a Total Basal Area and list the total in the appropriate space at the bottom of each Dominance section.
  • divide the Total Basal Area by the number of individuals of the species to determine the Mean Basal Area.
  • multiply the species Mean Basal Area by the No. Trees/ha (from column C6 in the Relative Density section) to determine the Dominance by species:

Dominance = Mean Basal Area x (No. Trees/ha)

= 0.071 x 80= 5.68

  • Dominance is determined for each species.

5. Determine the Relative Dominance of all species in the tree stratum. This is done in the same way as for Relative Density and Relative Frequency.

  • list each tree species encountered under “Species” in the Relative Dominance table.
  • list the corresponding Dominance values.
  • sum the Dominance column and list the total in the appropriate Total box.
  • calculate Relative Dominance (remember that relative values are out of 100):

Relative Dominance

= Species Dominance (of a species)  Total Dominance (of all species)

= (5.68  24.64) x 100= 23.1 (for jack pine)

  • sum all the Relative Dominance values. These should total 100. If this is not the case, then there has been an error in the calculations. Review and redo, if necessary, the preceding steps until this total equals 100.

6. Determine the Importance Value for all species in the tree stratum.

  • list each tree species and its corresponding Relative Density, Relative Dominance and Relative Frequency.
  • sum across the rows to determine an Importance Value for each of the species in the tree stratum.
  • sum each column (all the Relative values and the Importance Values). If all calculations have been performed correctly, all the Relative values will sum to 100 and the Importance Value will sum to 300. If this is not the case, then review your calculations, to find and correct the error.
  • transfer the Importance Value by species to Part 4 - Combined Strata (under the column “Tree Importance Value”).

Part 2 - Shrub Stratum

(sample calculations are based on balsam fir occurring in 5 points as per step 1 example)

1. Determine the Mean Percent Cover (for each species) by summing the total percent cover listed and dividing it by the total number of points.

Mean Percent Cover = Total Percent Cover  Number of points

= (30  10  50  20  30)  10= 14%

  • sum the Mean Percent Cover for all species and list the total in the appropriate Total box.

2. Determine the Frequency of occurrence for each species in the shrub layer:

Frequency = (No. of points the species occurs in  total number of points ) x 100

= (5  10) x 100= 50

  • sum the Frequency values for all species and list the total in the Total box at the bottom of the page.

3. Determine the Relative Dominance:

Relative Dominance

=(Mean percent cover of species  Total Mean percent Cover) x 100

= (14  39) x 100= 36

  • sum the Relative Dominance values for all species and list the total in the appropriate total box at the bottom of the page. This sum should equal 100.
  • Note that the Relative Dominance for both the Shrub and Herb/Moss layers is based on Mean Percent Cover, rather than basal area (as in the Tree stratum).

4. Calculate the Relative Frequency:

Relative Frequency = (Frequency of the species  Total Frequency) x 100

= (50  190) x 100= 26

  • sum the Relative Frequency values for all species and list the total in the appropriate total box at the bottom of the page. This sum should equal 100.

5. Calculate the Importance Value for all species in the Shrub stratum:

Importance Value = Relative Dominance  Relative Frequency

= 36  26= 62

  • sum the Importance Values for all species and list the total in the appropriate total box at the bottom of the page. Note that the Importance value in the Shrub layer should total 200; if not, then review the calculations.

6. Transfer the Importance Value for all species to Part 4 - Combined Strata under the Shrub column.

Part 3 - Herb and Moss Stratum

Mean Percent Cover, Frequency, Relative Dominance, Relative Frequency and Importance Value are all calculated in the same way for the Herb and Moss Stratum as they were in the Shrub layer.

Part 4 - Combined Strata

1. Sum the Importance Value by species for the Tree, Shrub and Herb/Moss layers (across rows):

Total Importance Value (TIV) of a species = Tree IV + Shrub IV + Herb IV

TIV (for balsam fir)= 0 + 62 + 86= 148

List this value under the Total column for the species

2. Sum each of the three Importance Value columns (i.e. Tree, Shrub, and Herb/Moss) and list the total at the bottom of the last page. Note that the Importance Values for the tree layer should sum to 300 (Relative Density + Relative Dominance + Relative Frequency) while the Shrub and Herb/Moss Importance Values should sum 200 each (Relative Dominance + Relative Frequency).

3. Sum the Importance Value “Total” column to ensure that it totals 700; this is the same total you should get when the individual Tree, Shrub and Herb/Moss Importance Values are added together. Be sure to carry out the cross check.

Conclusion

Once all calculations have been completed, marked and returned to you, the results will be used to describe your forest community (Laboratory 2). Use of a larger data base would provide a clearer ‘picture’ of the forest as you go about interpreting this data but we will be content with only one set per forest community. When you write the next paper, be sure to utilize information that is found in each of the three strata. Not only should you address the issues of which species occur in which strata and why, but also what do the relative values tell you about the structure of each layer? How do these relative values affect the Total Importance Value, and why must they be taken into consideration in describing the community?

Table 1. Completed field sheets for an example forest stand

Latitude: 48° 1'Longitude: 89° 2'Stratum: Tree

Observer(s): FarmerDate: July 22, 1992

Point / Quarter / Distance
(m) / Species / Diameter
(cm) / Point / Quarter / Distance
(m) / Species / Diameter
(cm)
1 / 1 / 2.1 / Sb / 15.0 / 7 / 1 / 2.2 / Bw / 10.5
2 / 3.1 / Sb / 13.5 / 2 / 1.0 / Bw / 11.0
3 / 3.5 / Sb / 13.0 / 3 / 1.8 / Bw / 11.0
4 / 2.7 / Sb / 13.0 / 4 / 3.2 / Bw / 9.0
2 / 1 / 2.4 / Pj / 34.0 / 8 / 1 / 2.7 / Sb / 15.0
2 / 1.5 / Sb / 12.0 / 2 / 1.7 / Sb / 9.5
3 / 1.3 / Sb / 10.5 / 3 / 2.1 / At / 14.0
4 / 1.3 / Sb / 15.5 / 4 / 2.5 / Bw / 11.5
3 / 1 / 2.1 / Sb / 8.5 / 9 / 1 / 2.4 / Bw / 8.5
2 / 3.1 / Bw / 13.0 / 2 / 1.1 / Sb / 8.0
3 / 2.1 / Bw / 19.5 / 3 / 1.4 / At / 8.5
4 / 0.8 / Bw / 11.0 / 4 / 3.7 / At / 12.0
4 / 1 / 1.7 / Sb / 22.0 / 10 / 1 / 2.3 / Sb / 8.0
2 / 0.7 / Bw / 13.0 / 2 / 1.5 / Bw / 13.0
3 / 3.0 / Bw / 13.0 / 3 / 1.0 / Sb / 14.0
4 / 2.9 / Sb / 21.0 / 4 / 4.4 / Sb / 11.0
5 / 1 / 2.9 / Sb / 13.0
2 / 2.0 / Bw / 9.5
3 / 2.8 / Bw / 10.5
4 / 2.6 / Bw / 8.0
6 / 1 / 9.1 / At / 14.0
2 / 3.5 / At / 9.5
3 / 3.1 / Pr / 8.0
4 / 3.3 / Pj / 26.0
Total Distance = 98.6 m
Number of trees = 40
Mean distance = 2.5 m / Number of trees/ha = 10,000 = 1600
(mean distance)2

Table 2. Example of calculations

Relative Density / Relative Frequency
Species / No.
in
Qtrs. / Total in
Qtrs. / Spec
Dens / Mean
Dens. / No.
Trees
per ha / Rel.
Dens. / Species / No.
Pts. / Tot.
Pts. / Freq. / Rel.
Freq.
C1 / C2 / C3 / C4
(C2/C3) / C5 / C6
(C4x
C5)
Pj / 2 / 40 / 0.05 / 1600 / 80 / 5 / Pj / 2 / 10 / 20 / 10
Bw / 15 / 40 / 0.38 / 1600 / 608 / 38 / Bw / 7 / 10 / 70 / 33
Sb / 17 / 40 / 0.43 / 1600 / 688 / 43 / Sb / 8 / 10 / 80 / 38
At / 5 / 40 / 0.12 / 1600 / 192 / 12 / At / 3 / 10 / 30 / 14
Pr / 1 / 40 / 0.02 / 1600 / 32 / 2 / Pr / 1 / 10 / 10 / 5
Total / 1600 / 100 / Total / 210 / 100
Dominance
Spp. / Diam
(cm) / BA
(m2) / Spp / Diam
(cm) / BA
(m2) / Spp. / Diam
(cm) / BA
(m2) / Spp. / Diam
(cm) / BA
(m2)
Pj / 34.0 / .090 / Sb / 15.0 / .018 / Bw / 13.0 / .013 / At / 14.0 / .015
26.0 / .053 / 13.5 / .014 / 19.5 / .030 / 9.5 / .007
13.0 / .013 / 11.0 / .010 / 14.0 / .015
Total BA = .143 m2 / 13.0 / .013 / 13.0 / .013 / 8.5 / .006
Mean BA = .071 m2 / 12.0 / .011 / 13.0 / .013 / 12.0 / .011
Dominance* = 5.68 / 10.5 / .009 / 9.5 / .007
15.5 / .019 / 10.5 / .009 / Total BA = .054 m2
8.5 / .006 / 8.0 / .005 / Mean BA = .011 m2
Pr / 8.0 / .005 / 22.0 / .038 / 10.5 / .009 / Dominance* = 2.07
21.0 / .035 / 11.0 / .010
Total BA = .005 m2 / 13.0 / .013 / 11.0 / .010
Mean BA = .005 m2 / 15.0 / .018 / 9.0 / .006
Dominance* = 0.16 / 9.5 / .007 / 11.5 / .010
8.0 / .005 / 8.5 / .006
8.0 / .005 / 13.0 / .013
14.0 / .015
11.0 / .010
Total BA = .249 m2
Mean BA = .015 m2
Dominance* = 10.08 / Total BA = .164 m2
Mean BA = .011 m2
Dominance* = 6.65

Basal Area (BA) in m2 = (diameter in cm)2 x .00007854 OR

Basal Area (BA) in dm2 = (diameter in cm)2 x .007854

* Dominance (m2/ha) = Mean BA x No. Trees/ha

Table 2. Example of calculations (con't)

Relative Dominance
Species / Dominance / Relative Dominance
Pj / 5.68 / 23
Sb / 10.08 / 41
Bw / 6.65 / 27
At / 2.07 / 8
Pr / 0.16 / 1
Total / 24.64 / 100
Importance Value
Species / Rel.
Den. / Rel.
Dom. / Rel.
Freq. / Imp.
Val.
Pj / 5 / 23 / 10 / 38
Sb / 43 / 41 / 38 / 122
Bw / 38 / 27 / 33 / 98
At / 12 / 8 / 14 / 35
Pr / 2 / 1 / 5 / 7
Total / 100 / 100 / 100 / 300

Summary Sheets for the Phytosociological Analysis of Field Data

Tree Stratum (Step 2)

Relative Density
Species / Number in
Quarters / Total.in
Quarters / Species
Density / Mean
Density * / Number of
Trees/ha / Relative
Density
C1 / C2 / C3 / C4
C2/C3 / C5 / C6
C4xC5
Totals /  / 100

* expressed in number of trees/ha

Tree Stratum (Step 3)

Relative Frequency
Species / Number of
Points / Total Number
of Points / Frequency
% / Relative
Frequency
C1 / C2 / C3 / C4
(C2/C3) / C5
(C4/C4
Totals /  / 100

Tree Stratum (Step 4)

Relative Dominance
Species 1 - / Species 2 - / Species 3 - / Species 4 -
Dbh
(cm) / BA
(m2) / Dbh
(cm) / BA
(m2) / Dbh
(cm) / BA
(m2) / Dbh
(cm) / BA
(m2)
Total BA = m2 / Total BA = m2 / Total BA = m2 / Total BA = m2
Mean BA = m2 / Mean BA = m2 / Mean BA = m2 / Mean BA = m2
Dom.* = m2/ha / Dom. = m2/ha / Dom. = m2/ha / Dom. = m2/ha
Relative Dominance
Species 5 - / Species 6 - / Species 7 - / Species 8 -
Dbh
(cm) / BA
(m2) / Dbh
(cm) / BA
(m2) / Dbh
(cm) / BA
(m2) / Dbh
(cm) / BA
(m2)
Total BA = m2 / Total BA = m2 / Total BA = m2 / Total BA = m2
Mean BA = m2 / Mean BA = m2 / Mean BA = m2 / Mean BA = m2
Dom. = m2/ha / Dom. = m2/ha / Dom. = m2/ha / Dom. = m2/ha

Basal Area (BA) in m2 = (diameter in cm)2 x .00007854

* Dominance (m2/ha) = Mean BA x No. Trees/ha (C6)

Tree Stratum (Steps 5 and 6)

Relative Dominance and Importance Value
Species / Dominance
(from Step 4) / Relative Dominance / Relative Density / Relative Frequency / Importance Value
Total /  / 100 / 100 / 100 / 300

Shrub Stratum (Steps 1 to 5)

Relative Dominance and Relative Frequency
Species / Mean %
Cover / Relative Dom. / Freq. / Relative Freq. / Importance Value
C1 / C2 / C3 / C4 / C5 / C6
(C2/C2) / (C4/C4) / (C3+C5)
Total /  / 100 /  / 100 / 200

Herb and Moss Stratum (steps 1 to 5)

Relative Dominance and Relative Frequency
Species / Mean %
Cover / Relative Dom. / Freq.
(%) / Relative Freq. / Importance Value
C1 / C2 / C3 / C4 / C5 / C6
(C2/C2) / (C4/C4) / (C3+ C5)
Total /  / 100 /  / 100 / 200
Combined Strata
Importance Value / Total Importance
Species / Tree / Shrub / Herb/Moss / Value
Total

Comments ______

______

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Forest Ecology and Silvics