BSCI 124 Lecture Notes
Undergraduate Program in Plant Biology, University of Maryland
LECTURE 34 - PLANT SUCCESSION
I. Plant succession - a series of predictable changes over time
in the kinds of plants growing in an area
A. Ecosystems mature and change with time
II. Primary succession
B. As ecosystems age, the kinds of organisms found in them changes until
some stable type of community forms
1. Always determined by the physical parameters of the environment
C. The relatively stable community at the end of succession is called a
1. Initial stages- high rate of replacement, unstable (prone to erosion
and wind damage)
2. Later stages- low rate of community change, more stable
D. In characterizing succession, we only list the dominant plants (the
ones that shape the ecosystem)
1. Climax community is thought to be in equilibrium with the environment
2. Permanent until there is some type of environmental change (flood,
3. Climax varies depending on the local conditions
4. Climax in some Maryland habitats is a hardwood
forest, in some California habitats is a grassland,
and in some Arizona habitats is a desert
E. Two kinds of succession, primary succession and secondary succession
A. Primary succession occurs when plants become established on land completely
devoid of soil and vegetation
III. Secondary succession
B. Succession on barren rock or lava (example: Mount
is that portion of the earth's surface consisting of disintegrated rock
and organic materials or humus. Primary succession is the development of
soils. The plant communities will generally change as the soil develops.
Lichens (pioneer species) --> mosses & ferns --> grasses --> shrubs
1. Possible primary succession for a forest habitat:
C. What is soil?
2. Each stage alters the habitat in such a way that it prepares the way
for the next invasion of species
a. bare rock is first colonized by lichens
b. small amount of soil formed by the lichens is colonized by mosses,
which do not have roots and require little soil, and ferns
c. as the seedless plants live and die, the soil continues to develop
to the point that grasses can successfully grow and a grassland
d. over time, the soil level increases to the point that shrubs can
grow in the grassland. The grassland is replaced by a shrub community
e. shrub community may be replaced by a forest
3. As succession proceeds, soil
is formed and thickens - the result of decomposition
4. When the changes in the composition of plants stop and the plant
community remains generally the same for many years, the community is mature
or at climax. A climax community is the relatively stable community at
the end of succession.
D. Succession on a body of water such as a pond or lake
1. Soil provides essential nutrients to all land plants, including water
and mineral nutrients.
2. Soil is the product of the living environment and is influenced
by climate, topography, parent material, and time.
a. 4.5 billion years ago, Earth was little more
than a mixture of rocks.
b. These rocks were transformed by glaciers, wind,
rain, and organisms into soil.
c. In eastern North America, where rainfall is abundant,
it can take more than
200 years to form only 2 cm of soil.
3. Soil characteristics (soil
material - soil particles consist of naturally occurring inorganic
compounds usually made of two or more elements.
texture - all soils contain three kinds of soil particles: sand, silt,
with different kinds of soils having different proportions
of particles. Clay is the
most important soil particle because its structure
helps hold nutrients, then
available to the plants.
matter - humus
organic matter in the soil.
occurs through the action of bacteria and fungi. Earthworms,
beetles, and termites mix the humus into the parent
material of the soil.
i. humus is lightweight
and spongy which aids in its water-holding capacity
ii. humus is rich in organic
iii. humus swells and shrinks
as it absorbs water and dries, aerating the soil; air
in the soil is necessary
for cellular respiration in the roots
iv. humus is a reservoir
for plant nutrients
v. most plants grow best
in 10-20% humus
d. soil pH - directly influences soil fertility
and the availability of nutrients. When
soils are acidic (low pH), nutrients are very soluble
and can easily be removed by
plants from the soil. However, acidic soils
increase the release of ions, such as
aluminum, which can poison the soil. When
soil is basic or alkaline (high pH),
nutrients become insoluble and are difficult to
for plants to remove. Maximum
soil fertility occurs when the pH is neutral or
4. Throughout history, soil water content, fertility, and productivity
have been the determining factors for humanity's standard of living.
(single-celled algae) -> submerged aquatic plants (Elodea)
-> floating plants (water
lilies ) -> rooted emergents/bog plants (cattails,
2. over time, these plant communities accumulate organic debris and silt
a. submerged aquatics are limited by light
b. rooted emergents are limited by depth
3. eventually pond is completely filled in and plant communities undergo
succession characteristic of a particular area
a. this fills in the pond
b. because it is shallower at the edges, they
fill in first and the edge of the pond moves toward the center
a. in Maryland the progression will be: woody shrubs and trees that can
tolerate a high water table (willows and red maple) --> pine --> deciduous
forest (climax- oak, hickory) with understory of holly and dogwood
A plant community may be disturbed causing some plants to be destroyed,
as from a fire or from human logging or cultivation. If the disturbance
stops, the community will begin a secondary succession, changes in the
vegetation that will lead back to a climax community.
IV. Why is it important for you to know about succession?
A. The progression of plant communities occurring on areas where there
has been previous vegetation (destroyed by fire,
B. Since the soil is already in place, secondary succession can
take place five to ten times faster than primary succession.
C. It is important to remember that the abiotic factors (such as weather,
humidity, and temperature) affect the nature of the plant community.
D. Also the plant community affects these abiotic factors. Therefore,
if a plant community is significantly disturbed, the loss of the vegetation
may change the abiotic conditions. If this occurs and the habitat has changed,
secondary succession may lead to a different climax community.
E. Example: secondary succession on abandoned farm in Maryland
1. An example is the tropical rain forest. The forest "creates" the rainfall
through the process of transpiration (the water in the air comes from the
water that has evaporated from the leaves). When the trees are removed,
the rainfall stops. The land then becomes arid. The resulting new climax
community is often desert shrubs
1. Annuals (weeds like crabgrass) 1-2 years
(herbs and tall grasses) 2-5 years
3. Young pine seedlings in tall grass 5-10 years
forest 10-150 years
hardwood forest (climax) 150+ years
A. You should understand that natural systems can maintain themselves,
whereas disturbed systems cannot.
Other sites of interest
B. Human influence on succession- generally, humans knock out the climax
C. Example of human interference with succession- producing a green,
1. Producing such a lawn means a constant battle against natural plant
2. What you must do to maintain such a system
3. Thus, when humans interfere with plant communities -> many problems
that would be controlled in a natural system (this same thing happens in
a. plant grass seed- to complete against natural seed dispersal of many
b. mow- limits the establishment of trees and other tall species
c. apply herbicides- to eliminate interspecific competition (competition
between different species) and to cut down on species diversity- must be
done because broad-leaved species are often more adaptable and successful
than grasses and can out-compete them
d. apply fertilizer- grass species use up soil nutrients quickly (particularly
when clippings are bagged)
e. irrigate- natural rainfall is often inadequate for lawn grass
f. apply fungicides and other chemicals to control disease and insect
pests- must be done because an unnatural ecosystem (such as a lawn) is
more prone to disruption
4. Without the continued interference of humans, the yard would have
a natural sequence of succession over time
succession, Ojibway Prairie Complex
- Okanagan University College
example - Alaska
example - Vermont
- University of Idaho
Got the lawnmower blues?
- Creating a natural yard.
BSCI 124 main page
Last revised: September 1, 1998 - Browning
updated Dec. 2000 - Straney