TITLE

Determining the diversity of plant species communities on the forest interior and forest edge on the UTM campus and testing the association of two plant species; garlic mustard and Crown Vetch

INTRODUCTION

The underlying purpose of this field exercise was to determine the two main

components of species diversity; richness and evenness. Richness is defined as

the number of species along a transect while evenness is the dominance or

distribution of species. In the first part of the exercise, In order to measure the

richness (species diversity), 20m line transects were laid in the forest interior and

forest edge on the UTM campus and the total number of individuals of each plant

species were recorded. In the second part of the exercise, to measure the

the association of two plant species; Garlic mustard and Crown vetch

was determined by looking for the presence or absence of the species within the

hoop. The hypothesis for the first part of the experiment would be that there will

be higher species diversity on the forest edge. The prediction for the first

exercise will be that more number of individuals will be found on the forest edge

along the transect (richness) and the distribution of species will be highly uneven

on the forest edge. The hypothesis for the second exercise will be that there will

be an association between Crown Vetch and Garlic mustard and the prediction

will be that both species will be present.

MATERIALS AND METHOD

The materials required in the exercise were two 20m line transects and a

document with pictures used to identify the different plant species commonly

found UTM. In the first part of the exercise (assessment of plant species diversity

in the forest interior and forest edge), two 20m transects were laid in groups in

the forest interior and forest edge respectively. Spanning a distance of 1m on the

transect, students in pairs of 2 identified and counted the total number of

individuals of different plant species and all the data reported was later

condensed into a table showing the total number of individuals of different plant

species found along the 20m transect in both the forest interior and edge. Based

on the findings in part 1, Jaccard’s index of similarity between the interior and

edge transects was calculated and the percent similarity was obtained. For part 2

of the exercise (testing the association of the 2 plant species), each student

randomly placed a hoop in the field and looked for the presence or absence of

Crown Vetch and Garlic mustard. Based on the results, a Chi-squared test was

performed to determine if there is indeed an association between the two

species.

RESULTS

Figure 1.1: The Bar Graph above shows the number of individuals of different plant species observed along a 20m line transect in the forest interior on the UTM campus 3
Figure 1.2: The Bar Graph above shows the log (number of individuals) of different plant species observed along a 20m line transect in the forest edge on the UTM campus

Jaccard’s Index of similarity

ISJ = c____ a + b – c

where a = total number of species along transect 1 b = total number of species along transect 2 c = number of species in common

Based on the results,

a = 7 (total number of species along the forest interior transect) b = 18 (total number of species along the forest edge transect)

c = 6 (number of species in common)

ISJ = 6 / (7+18-6)

ISJ = 0.3158

The percent similarity between the forest interior and forest edge is 31.58% (0.3158/1X100%)

Chi-Squared test

Contingency table

Crown Vetch Present Absent

Present 38
(36.6) 1
(2.4) 39
Absent 7
(8.4) 2
(0.6) 9 45 3 48

Garlic
Mustard

χ2 – Chi square

χ2 = ∑ (observed – expected)2 expected χ2 = 0.054 + 0.233 + 0.817 + 3.27 χ2 = 4.374

Based on the results in figure 1.1 and figure 1.2, it is apparent the forest edge

is much richer in species diversity in contrast to the forest interior. This is due to

the fact that the forest edge has 18 different plant species as opposed to the

forest interior which houses only 7 different plant species (fig 1.1 and fig 1.2). In

addition to that, there are more number of individuals found in the forest edge in

comparison to the forest interior. Based on the calculated Jaccard’s index of

similarity (0. 3158), the percent similarity between the forest edge and forest

interior is 31.58%. The chi-squared value obtained was 4.374. The critical value

for a contingency table with 2 colums and 2 rows (4 outcomes) and a 5% level of

significance is 3.84. As the calculated chi-squared value is more than the critical

value, it can be concluded that there is indeed an association between Crown

Vetch and Garlic mustard.

DISCUSSION

Based on the results, a higher number of individuals were found on the forest

edge (richness) and the distribution of plant species on the forest edge was

highly uneven (evenness) in comparison to the interior. The results obtained

supported the hypothesis and prediction for the first exercise. The richness of

species on the forest edge could be accounted for in terms of abiotic factors such

as temperature, light, soil richness and many more which enable certain plant

species to thrive. Grass species tend to thrive in this environment and grow at a

very rapid rate as a consequence of rich surrounding conditions and receiving

high sunlight (on the forest edge). As a result, this makes them the most

abundant species (Grass species 1- 14802, Grass species 2 – 1970) on the edge

causing the distribution of species to be highly uneven. On the other hand, the

forest interior was low in species diversity (richness) and was highly even. From

the Jaccard’s index of similarity (0.3158) and the percent similarity (31.58%)

between the forest edge and interior, it can be deduced that though the edge and

interior are not highly similar, they have a number of species in common (6

species). Based on the results from the second exercise, As the calculated chi-

squared value (4.374) is more than the critical value (3.84), it can be concluded

that there is indeed an association between Crown Vetch and Garlic mustard. A

possible ecological reason as to why these two species are found together is

symbiosis. Symbiosis is a process by which two independent species depend on

each other in several ways such as food, shelter and nutrients.