This series of predictable changes that occurs in a community over time is called ecological succession.In another words, Ecological succession is the change in species composition over time; that is, the replacement of one group of species by another group of species. There are two major types of ecological succession: primary succession and secondary succession. In primary succession, a site that is initially absent of species becomes colonized for the very first time. In secondary succession, a site that supports an existing assemblage of species experiences a disturbance that changes the composition of species. Both types of succession can occur in terrestrial and aquatic ecosystems. The first species to arrive and colonize the newly formed habitat are pioneer species. These early colonizers contribute nutrients to the soil through organic matter accumulation from decomposition. Some early successional plant species can fix atmospheric nitrogen and thereby increase nitrogen availability in the soil for other plants. As soil nutrients increase over succession it allows for the colonization of previously nutrient-limited species that were unable to establish initially. This facilitates the turnover in species composition over time. In terrestrial ecosystems, this compositional shift corresponds to a change in life forms and distinct species assemblages transitioning from small herbaceous plants, to shrubs, and ultimately to stands of trees over the course of succession. Secondary succession in terrestrial ecosystems can initiate after fire, tornadoes/ hurricanes, or humans disturb an already established plant community, removing most species but leaving the soil intact. The disturbance changes exposure of the habitat to sunlight, wind, and water that alters colonization and the assemblage trajectory of the new plant community. Some plant species may arrive to the disturbed site from

1. Asian University For Women
BIOL/ENVS 3003: Ecology Lab, Fall 2022
Ecological Succession (Lab#3)
This content is prepared by Sayed Mohammad Nazim Uddin (Ph.D., Head, Science & Math Program, Associate
Professor in Environmental Science) and Syed Mohammad Lokman (Adjunct Faculty, Bioinformatics and
Environmental Science), Asian University For Women, Chittagong, Bangladesh.
References are cited in between the contents.

2. Ecological Succession Lab
INTRODUCTION: Ecosystems are constantly changing in response to natural and
human disturbances. As an ecosystem changes, older inhabitants gradually die out and
new organisms move in, causing further changes in the community. This series of
predictable changes that occurs in a community over time is called ecological
succession.In another words, Ecological succession is the change in species
composition over time; that is, the replacement of one group of species by another
group of species. There are two major types of ecological succession: primary
succession and secondary succession.
In primary succession, a site that is initially absent of species becomes colonized for
the very first time. In secondary succession, a site that supports an existing
assemblage of species experiences a disturbance that changes the composition of
species. Both types of succession can occur in terrestrial and aquatic ecosystems.
The first species to arrive and colonize the newly formed habitat are pioneer species.
These early colonizers contribute nutrients to the soil through organic matter
accumulation from decomposition. Some early successional plant species can fix
atmospheric nitrogen and thereby increase nitrogen availability in the soil for other
plants. As soil nutrients increase over succession it allows for the colonization of
previously nutrient-limited species that were unable to establish initially. This
facilitates the turnover in species composition over time. In terrestrial ecosystems, this
compositional shift corresponds to a change in life forms and distinct species
assemblages transitioning from small herbaceous plants, to shrubs, and ultimately to
stands of trees over the course of succession.
Secondary succession in terrestrial ecosystems can initiate after fire, tornadoes/
hurricanes, or humans disturb an already established plant community, removing most
species but leaving the soil intact. The disturbance changes exposure of the habitat to
sunlight, wind, and water that alters colonization and the assemblage trajectory of the
new plant community. Some plant species may arrive to the disturbed site from

3. dispersal (animal, water, wind) while other species may establish from the existing seed
bank. Over time, species replacement yields successional stages similar to primary
succession. Secondary succession in aquatic ecosystems can initiate after a habitat
dries and refills, after sedimentation occurs, or a natural or artificial (human-imposed)
dam is constructed.
Figure A. Primary succession begins when no plant life is present on the landscape, such as
after a lava flow or glacial retreat. Over centuries, soil forms and deepens and successive
communities of plants grow.
> What is a climax community?
A climax community is the “endpoint” of succession within the context of a particular
climate and geography. In the midwestern U.S., for example, such a community might
be a hardwood forest with oaks and hickories as the dominant tree species. A climax
community will persist in a given location until a disturbance occurs. However, in
many ecosystems, disturbance occurs frequently enough that a matrix of community
types may be consistently present on the landscape.

4. Figure B. Secondary succession begins after a disturbance, like a fire. Crucially, some soil and
nutrients remain present—fire, in fact, may help recycle those nutrients.
Figure C. Forest succession depicted over time

5. Exercise 3.1: Ecological Succession Lab Date:
Name :____________________________________ ID: ______________
In this lab you will apply what you have learned
about succession to the ecological changes that
occur in an abandoned hay field. After only 5
years, several types of trees have begun to grow
where there was once only hay. You will observe, by
counting, the number and types of trees that grow in
this field 5, 20, 50 and 100 years after
abandonment, in both the understory and the
canopy.
Procedure A:
For each figure 1-6, count how many of each species of tree are found in the field,
using the key as a guide. Add up all of the trees to find the total number of trees present
in the field. You will now calculate the percentage of each tree species at each observed
time period. Use the following formula:
Number of specific tree ÷ TOTAL number of trees = _______ X 100 = ______%
Figure 1 (Understory and Canopy after 5 years) Figure 2 (Understory after 20 Years)

6. Figure 3 (Understory after 50 Years) Figure 4 (Canopy after 20 Years)
Figure 5 (Canopy after 50 Years) Figure 6 (Canopy after 100 Years)
Tree species Number of Trees % of Total
Fig
1
Fig
2
Fig
3
Fig
4
Fig
5
Fig
6
Fig 1 Fig 2 Fig 3 Fig 4 Fig 5 Fig 6
Yellow birch ◯
Aspen ▲
Pin cherry ◼
Blackberry ⬤
Sugar Maple ▢
Beech ◇
TOTAL

7. Procedure B (Graded Quiz):
● Using the data in the tables you just completed, construct two graphs.
○ The first graph will show the changes in the percentage of each tree
species in the understory from 5 to 50 years after the hay field was
abandoned. Use the percentages of each tree species from figures 1, 2,
and 3 to construct your graph of the understory changes.
○ The second graph will show the changes in the percentage of each tree
species in the canopy from 5 to 100 years after the hay field was
abandoned. Use the percentages of each tree species from figures 1, 4, 5
and 6 to construct your graph of the canopy changes.
● After completing both graphs, answer the following analysis questions.
Graph 1:
Graph 2:

8. Q1. Describe, in terms of decreasing or increasing percentage, what happened to each
of the following tree populations from 5 to 100 years after the field was abandoned:
a. Yellow birch - ____________________________________________
b. Aspen - _________________________________________________
c. Pin cherry - ______________________________________________
d. Blackberry - _____________________________________________
e. Sugar maple - ____________________________________________
f. Beech - _________________________________________________
Q2. Using the understory figures 2 and 3, which tree species disappeared between 20
and 50 years after the field was abandoned? (Note: do not include trees that had
already disappeared after 20 years.)
______________________________________________________________
______________________________________________________________
Q3. Use the canopy figures 4, 5 and 6 to answer the following questions:
a. Which tree species disappeared between 20 and 50 years after the field was
abandoned? ________________________________________________________
b. What tree species appeared between 20 and 50 years after the field was
abandoned? _________________________________________________________