Ecology
May 16, 2018
ASSESSMENT OF DISTRIBUTION, DENSITY AND IMPORTANCE VALUE OF
TREE COMMUNITY IN MINDANAO STATE UNIVERSITY
Nasser M. Sabandal
Secondary Education Department, College of Education, Mindanao State University General
Santos City 9500
Abstract
Ecologists face the need to estimate the number of individuals present in a
population or community. Conveniently, it would be impractical to count all of the
individuals so, coming up with the appropriate methods kicks in here. Assessment of
distribution, density, and importance value of trees would be quite heavy in the part of
Ecologist because sampling of trees would be very difficult especially if the area to be
sample is large. So, this study utilizes Point-Quarter Method to assess the distribution,
density and importance value of tree community in ROTC Headquarters, Mindanao State
University specifically aims to achieve the following objectives: (1) determine the
density, cover dominance and frequency of each tree species. (2) Determine the
importance value. The results obtained showed that Neem Tree and Ipil-ipil have high
relative density and relative frequency compare to Malunngay, Palm Tree and Tamarind with
low relative density and frequency, three (3) plants appeared to have the highest importance
value of 50.8, 60.1, and 50.8 respectively. Accordingly, we can conclude that Neem Tree and
Ipil-ipil have high distribution in the area. We can also posit that Neem Tree, Ipil-ipil and
Mango have high importance in the community. Notwithstanding, the research have some
shortcomings in obtaining the complete and sound health of the tree community occupying
the area, so, it is advisable the pioneer researcher will include the soil moisture, pH level, and
light intensity in the area as a parameters.
Keywords- density, frequency, importance value, Point-Quarter Method
INTRODUCTION
In studying number of individual present in a population or community there is the
need to use a methodology which will appropriate, convenient disregard subjective biases.
Oftentimes, Ecologists face the need to estimate the number of individuals present in a
population or community. Conveniently, if there are few large individuals, then it can be
done directly by counting each individual. Meanwhile, if there are many individuals, the
community is large, or the individuals are small. It would be impractical to count all of the
individuals so, coming up with the appropriate methods kicks in here.
Assessment of distribution, density, and importance value of trees would be quite
heavy in the part of Ecologist because sampling of trees would be very difficult especially if
the area to be sample is large. Plot sampling (quadrats, belts) is unwise to use in describing
the tree community, so it may easiest to sample trees by utilizing plotless techniques. Since
trees are stationary organisms, plotless technique would be best option because it involves
measurement of distance and girth of sample tree.
In one hand, our country is also one of the ‘biodiversity hotspot’ where extinction of
species endemics showed an alarming rate. This is evident as mentioned by Medina (2014)
that Foundation of Philippine Environment reported that Philippine forests deforestation have
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May 16, 2018
been dwindling at an average rate of 2% per annum (rate of 550,000 hectares a year or 63
hectares per hour) – one of the highest in the world. We also have some threatened endemic
fauna of 711 and flora of 984 (DENR, 2018). So, considering trees have significant
ecological value because it supports local wildlife, serves as a corridor between other
important habitats and nesting site for other birds. Those species that are dependent on the
tree are themselves of ecological importance.
Consequently, the application of plotless survey method like Point-Quarter Method is
more effective compare to that of plot-less methods as it provides more estimate of density
(Beasom and Haucke, 1975). So, this study utilizes Point-Quarter Method to assess the
distribution, density and importance value of tree community in Mindanao state university.
In doing this, the study aimed specifically to achieve the following objectives;
1. Determine the density, cover dominance and frequency of each tree species.
2. Determine the importance value.
METHODS & MATERIALS
The procedure outlined below describes how to carry out point-centered quarter
method data collection along a 100 m transect. It can be scaled up or down, as appropriate,
for longer or shorter transects. While this analysis can be carried out alone, groups of two or
three can make for very efficient data collection. Material requirements include 50 or 100
meter tape, a shorter 5 or 10 meter tape, a notebook, a calculator, and a table of random
numbers if the calculator cannot generate them.
1. Generate a list of 15 to 20 random two-digit numbers. If the difference of any two is 4
or less, cross out the second listed number. There should be 10 or more two-digit
numbers remaining; if not, generate additional ones. List the first 10 remaining
numbers in increasing order. It is important to generate this list before doing any
measurements.
2. Lay out a 100 m transect (or longer or shorter as required).
3. The random numbers represent the distances along transect at which data will be
collected. Random numbers are used to eliminate bias. Everyone always wants to
measure that BIG tree along the transect, but such trees may not be representative of
the community.1 The reason for making sure that points are at least 5 meters apart is
so that the same trees will not be measured repeatedly. Caution: If trees are
particularly sparse, both the length of transect and the minimum distance between
points may need to be increased.
4. The smallest random number determines the first sampling point along transect. At
this (and every sampling) point, run an imaginary line perpendicular to transect. This
line and transect divide the world into four quarters (hence the name, point-centered
quarter method).
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May 16, 2018
Figure 1. Sample points along a transect with the nearest trees in each quarter
indicated by · · · · · ·
5. Select one of the quarters. In that quarter, locate the tree nearest to the sampling point.
For the purposes of this exercise, to be counted as a “tree” it should have a minimum
diameter of 4 cm or, equivalently, a minimum circumference of 12.5 cm. (Caution: In
other situations, different minimum values may apply.)
For the each sampling point, record:
(a) the quarter number (I, II, III, or IV);
(b) the distance from the sampling point to the center of the trunk of the tree to the
nearest 0.1 m (Caution: Review Appendix A on the 30–300 Rule.);
(c) the species of the tree; and
(d) the diameter at breast height (DBH) or circumference at chest height (CCH) to the
nearest cm, but again observe the 30–300 Rule.
6. Repeat this process for the entire set of sampling points.
7. Carry out the data analysis as described below. For trees with multiple trunks at breast
height, record the diameter (circumference) of each trunk separately. What is the
minimum allowed diameter of each trunk in such multi-trunk tree? Such decisions
should be spelled out in the methods section of the resulting report. At a minimum,
one should ensure that the combined cross-sectional areas of all trunks meet the
previously established minimum cross-sectional area for a single trunk tree. For
example, with a 4 cm minimum diameter for a single trunk, the minimum cross-
sectional area is
πr2 = π (2)2 = 4π ≈ 12.6 cm2
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May 16, 2018
Field Sampling
This research utilized Point-Quarter Method to collect sample in area situated in
ROTC Headquarter, GSC, 6°3’46” N, 125°7’41”E. The data collection started from 2:00 PM
to 4:00 PM afternoon at 33˚C. Having 60% humidity during the day of May 14, 2018. The
sampling site was slightly bushy with some sandburs.
Plants and Animals Identification
Using Google Image Search, the researchers identify the plants by either describing
the characteristics of the specimens or dragging the pictures. PictureThis app is also utilized
to scan the picture of plants specimens.
Data Analysis
The researcher utilized the protocol for data analysis for Point-Quarter Method
(Cottam, Curtis, and Hale, 1953).
Density
Absolute Density
The absolute density λ of trees is defined as the number of trees per unit area.
Since λ is most easily estimated per square meter and since a hectare is 10,000
m2, λ is often multiplied by 10,000 to express the number of tree per hectare.
The distances measured using the point-centered quarter method may be used to
estimate λ to avoid having to count every tree within such a large area.
Note that if λ is given as trees/m2, then its reciprocal 1/λ is the mean area
occupied by a single tree.
This observation is the basis for the following estimate of λ.
From the transect information, determine the mean distance r¯, which is the
sum of the nearest neighbor distances in the quarters surveyed divided by the
number of quarters,
Mean distance r= 5.93 m
Absolute density= 0.0284 trees/m2
Cottam, Curtis, and Hale (1953) showed empirically and Morisita (1954) demonstrated
mathematically that r¯ is actually an estimate of √ 1/ ƛ , the square root of the mean area
occupied by a single tree.
Consequently, an estimate of the density is given by
Absolute Density of Each Species
The absolute density of an individual species is the expected number of trees of that
species per square meter (or hectare). The absolute density λk of species k is estimated as
the proportion of quarters in which the species is found times the absolute density of all
trees.
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May 16, 2018
Relative Density of a Species
The relative density of each species is the percentage of the total number observations of
that species,
Cover or Dominance of a Species
Absolute Cover
The cover or dominance of an individual tree is measured by its basal area or cross-
sectional area.
Let d, r, c, and A denote the diameter, radius, circumference, and basal area of a tree,
respectively. Since the area of a circle is A = πr2, it is also A = π (d/2)2 = πd2/4. Since the
circumference is c = 2πr, then the area is also A = c2/4π. Either A = πd2/4 or A = c2/4π can
be used to determine basal area, depending on whether DBH or CCH.
The first step is to compute the basal area for each tree sampled, organizing the data by
species. This is the most tedious part of the analysis. A calculator that can handle lists of
data or a spreadsheet can be very handy at this stage. The basal area for each tree was
obtained using the formula A = πd2/4. For trees with multiple trunks, the basal area for each
trunk was computed separately and the results summed.
No. /ha
(Species) = Mean BA in cm2
Relative Cover (Relative Dominance) of a Species
The relative cover or relative dominance [see Cottam and Curtis (1956)] for a
particular species is defined to be the absolute cover for that species divided by the total
cover times 100 to express the result as a percentage. The relative covers should sum to
100% plus or minus a tiny round-off error.
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May 16, 2018
The Frequency of a Species
Absolute Frequency of a Species
The absolute frequency of a species is the percentage of sample points at which a
species occurs. Higher absolute frequencies indicate a more uniform distribution of a
species while lower values may indicate clustering or clumping. It is defined as,
Relative Frequency of a Species
To normalize for the fact that the absolute frequencies sum to more than 100%, the
relative frequency is computed. It is defined as,
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May 16, 2018
RESULTS
Below shows the results obtained from survey which includes density and
frequency.
TABLE 1. THE LIST OF TREE SPECIES IN EACH POINT-QUARTER WITH COORDINATES, DISTANCE
AND GIRTH.
Sampling Quarter No. Coordinates Distance Girth
Point
1: Neem Tree 6°3’46” N, 125°7’41”E 2m 30cm
2: Mango Tree 6°4’15”N, 125°7’38”E 10m 270m
1 3: Malunggay 6°3’31”N, 125°7’47”E 3m 25cm
4: Ipil-ipil Tree 6°4’15”N, 125°7’47”E 15m 20cm
1: Mansanitas 6°4’15”N, 125°7’38”E 3m 25cm
2: Ipil-ipil 6°3’31”N, 125°7’47”E 3m 20cm
2 3: Neem Tree 6°4’9”N, 125°7’34”E 1m 10cm
4: Malunggay 6°4’15”N, 125°7’38”E 1m 5cm
1: Neem Tree 6°3’31”N, 125°7’47”E 3m 50cm
3 2: Mansanitas 6°4’15”N, 125°7’38”E 3m 40cm
3: Ipil-ipil 6°3’54”N, 125°7’44”E 5m 30cm
4: Tamarind 6°3’31”N, 125°7’47”E 1m 35cm
1: Ipil-ipil 6°3’49”N, 125°7’5”E 5m 20cm
4 2: Mansanitas 6°3’31”N, 125°7’47”E 35m 15cm
3: Neem Tree 6°4’15”N, 125°7’38”E 5m 50cm
4: Palm Tree 6°3’31”N, 125°7’47”E 7m 35cm
1: Ipil-ipil 6°4’9”N, 125°7’34”E 4m 40cm
5 2: Neem Tree 6°3’46”N, 125°7’29”E 6m 100cm
3: Neem Tree 6°3’31”N, 125°7’47”E 3m 60cm
4: Gemelina 6°4’9”N, 125°7’34”E 4m 80cm
1: Neem Tree 6°4’9”N, 125°7’34”E 2m 125cm
6 2: Ipil-ipil 6°3’31”N, 125°7’37”E 5m 20cm
3: Neem Tree 6°4’15”N, 125°7’38”E 4m 150cm
4: Gemelina 6°3’31”N, 125°7’47”E 10m 60cm
1: Ipil-ipil 6°3’48”N, 125°7’40”E 4m 20m
2: Gemelina 6°3’31”N, 125°7’34”E 2m 40m
7 3: Neem Tree 6°4’9”N, 125°7’34”E 15m 120cm
4: Ipil-ipil 6°4’9”N, 125°7’36”E 5m 20cm
Total
166
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May 16, 2018
Species Curve
9
6
No. of Species
0
1 2 3 4 5 6 7
Sampling Point
Figure 2. Species curve which is use as and indicative to the limit of sampling.
TABLE 2. The absolute density of each species.
SPECIES FREQUENCY/QUARTER TREES/HA
Gemelina 3/28=0.11 0.11 X 0.0284=0.003
Ipil-ipil 8/28=0.29 0.29 X 0.0284=0.008
Malunggay 2/28=0.07 0.07 X 0.0284=0.002
Mango Tree 1/28=0.04 0.04 X 0.0284=0.001
Mansanitas 3/28=0.11 0.11 X 0.0284= 0.003
Neem Tree 9/28=0.32 0.32 X 0.0284=0.009
Palm Tree 1/28=0.04 0.04 X 0.0284=0.001
Tamarind 1/28=0.04 0.04 X 0.0284=0.001
TOTAL
0.028
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May 16, 2018
Figure 3. The relative density of each species.
TABLE 3. The absolute cover of each species.
SPECIES ABSOLUTE FREQUENCY
Gemelina (3/7) X 100= 42.86
Ipil-ipil (8/7) X 100= 114.29
Malunggay (2/7) X 100=28.57
Mango tree (1/7) X 100=14.29
Mansanitas (3/7) X 100=42.86
Neem tree (9/7) X 100=128.57
Palm tree (1/7) X 100=14.29
Tamarind (1/7) X 100=14.29
Total 400.02
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Figure 4. The relative frequency of each species.
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May 16, 2018
TABLE 4. The basal area of each tree.
Gemelina Ipil-ipil Malunngay Mango Mansanitas Neem Tree Palm Tree Tamarind
Total
D130 Area D13 Area D13 Area D13 Area D130 Area D130 Area D130 Area D130 Area
(cm) (cm2) 0 (cm2) 0 (cm2) 0 (cm2) (cm) (cm2) (cm) (cm2) (cm) (cm2) (cm) (cm2)
(cm) (cm) (cm)
252 50009.4 63 3125.5 78 4791.1 850 568968.7 78 4791.1 94 6958.3 110 9528.7 110 9528.7
189 28130.2 63 3125.5 15 177.1 126 12502.3 31 756.7
126 12502.3 94 6958.3 47 1739.5 157 19411.0
63 3125.5 157 19411.0
126 12502.3 315 78139.6
63 3125.5 189 28130.2
63 3125.5 393 121628.5
63 3125.5 472 175442.4
378 112521.1
Total BA 90641.9 38213.6 4968.2 568968.7 19032.9 562398.8 9528.7 9528.7 1303281.5
X
Mean BA 30213.9 4776.7 2484.1 568968.7 6344.3 62488.7 9528.7 9528.7 694333.8
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May 16, 2018
Table 5. The total basal area of each species.
Species Mean BA (cm2) No. /Ha Total BA/ Ha (m2/ha)
Gemelina 30213.9 0.003 0.009
Ipil-ipil 4776.7 0.008 0.001
Malunggay 2484.1 0.002 0.0005
Mango tree 568968.7 0.001 0.057
Mansanitas 6344.3 0.003 0.002
Neem tree 62488.7 0.009 0.056
Palm tree 9528.7 0.001 0.001
Tamarind 9528.7 0.001 0.001
Total 0.1275
Figure 5. The relative cover of each species.
TABLE 6. The importance value of each species.
Species Relative Relative Relative Importance
Density Cover Frequency
Gemelina 10.7 7.0 10.7 28.4
Ipil-ipil 28.6 2.9 28.6 60.1
Malunggay 7.1 0.4 7.1 14.6
Mango tree 3.6 43.7 3.6 50.8
Mansanitas 10.7 1.5 10.7 22.9
Neem tree 32.1 43.2 32.1 107.4
Palm tree 3.6 0.7 3.6 7.9
Tamarind 3.6 0.7 3.6 7.9
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May 16, 2018
DISCUSSION & CONCLUSION
As shown the graph in figure 2, we can obtain that Neem Tree and Ipil-ipil have high
relative density compare to other trees. Moreover, the high relative frequency (see. Figure 2
and 3) indicates that the species occurs near relatively in many different sampling points, to
simply put, the species is well-distributed along transect. A high relative density indicates
that the species appears in a relatively large number of quarters (Mitchell, Kevin 2007).
Consequently, as shown the figure 2 and 4 (see graph in fig. 2 & 3) the three trees
namely; Malunngay, Palm Tree and Tamarind have low relative density and frequency thus
means that the species have appears in just on quarter in a point. Furthermore, if the relative
density is high and the relative frequency is low, then the species must appear in lots of
quarters but only at a few points then the distribution is in clumps but this feature in not
apparent in the data obtained (see Table 6) where the relative density and relative frequency
are very close. Whereas, if both are high, the distribution is relatively even and relatively
common along transect as can be observe to be apparent in Ipil-ipil and Neem Tree.
On the other hand, the importance value of three (3) plants appeared to have the
highest importance value of 50.8, 60.1, and 50.8 respectively. This result is an indication that
they are the most important species within the community. Although, as we can observed that
the frequency and density of Mango is relatively low it turns out to have high importance
value because of its apparent large basal or cover dominance of 568968.7 (see Table 5).
Moreover, Neem Tree and Ipil-ipil have the largest importance value because of their high
relative density, and frequency which also add up as factors in determining the importance
value of tree in a community. This indication simply means that small trees (i.e., with small
basal area) can be dominant only if there are enough of them widely distributed across
transect which are evident in the case of Neem Tree and Ipil-ipil. Accordingly, as shown in
the result obtained we can conclude that Neem Tree and Ipil-ipil have high distribution in the
area. We can also posit that Neem Tree, Ipil-ipil and Mango have high importance in the
community. Notwithstanding, the research have some shortcomings in obtaining the complete
and sound health of the tree community occupying the area, so, it is advisable the pioneer
researcher will include the soil moisture, pH level, and light intensity in the area as a
parameters.
Literature Cited
Beasom, Samuel L. and Harry H. Haucke. 1975. A comparison of four distance sampling
techniques in South Texas live oak mottes. J. Range Management. 28: 142–144.
Cottam, Grant, J. T. Curtis, and B. W. Hale. 1953. Some sampling characteristics of a
population of randomly dispersed individuals. Ecology. 34: 741–757.
DENR. 2018. STATUS OF THE PHILIPPINE BIODIVERSITY. Biodiversity Management
Bureau.Retrieved from http://www.gov.ph.
Medina, Milton Norman D. 2014. PLECOPTERA FAUNA IN COMPOSTELA VALLEY
PROVINCE, MINDANAO ISLAND, PHILIPPINES.The Rufford Foundation.
Mitchell, Kevin 2007. Quantitative Analysis by the Point-Centered Quarter Method.
Department of Mathematics and Computer Science. 2.15: 1-34.
