How does lichens contribute to primary succession?

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

o 1. Always determined by the physical parameters of the environment
B. As ecosystems age, the kinds of organisms found in them changes until some stable type of community forms

o 1. Initial stages- high rate of replacement, unstable (prone to erosion and wind damage)

2. Later stages- low rate of community change, more stable
C. The relatively stable community at the end of succession is called a climax community

o 1. Climax community is thought to be in equilibrium with the environment

2. Permanent until there is some type of environmental change (flood, fire, wind, climate change)
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
D. In characterizing succession, we only list the dominant plants (the ones that shape the ecosystem)

E. Two kinds of succession, primary succession and secondary succession

II. Primary succession

* A. Primary succession occurs when plants become established on land completely devoid of soil and vegetation

o 1. Soil 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.

B. Succession on barren rock or lava (example: Mount St. Helens)

o 1. Possible primary succession for a forest habitat:

Lichens (pioneer species) --> mosses & ferns --> grasses --> shrubs --> trees
o
+ a. bare rock is first colonized by lichens and bacteria

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 community forms
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 2. Each stage alters the habitat in such a way that it prepares the way for the next invasion of species
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.

Last revised: September 1, 1998 - Browning
updated Dec. 2000 - Straney

Lichens contribute to primary succession by being pioneer species and aiding in the development of soil. In primary succession, plants establish themselves on land that is completely devoid of soil and vegetation. Initially, bare rock is colonized by lichens and bacteria. Lichens are unique organisms consisting of a symbiotic association between a fungus and an algal or cyanobacterial partner. They are able to grow on bare rock surfaces and secrete acids that help break down the rock, creating small amounts of soil.

As lichens continue to grow and die, they contribute organic matter to the soil and initiate the process of soil development. This enables other plants, such as mosses and ferns, to colonize the area and further contribute to soil formation. With the presence of these seedless plants, the soil continues to develop and thicken. Eventually, the soil becomes suitable for grasses to grow, leading to the establishment of a grassland community.

Each stage of plant succession, including the colonization by lichens, alters the habitat and prepares the way for the next invasion of species. As the succession progresses, the soil continues to form and thicken due to decomposition. This allows for the establishment of shrubs, and eventually, a forest community may replace the shrub community.

Overall, lichens play a crucial role in primary succession by initiating soil formation and creating favorable conditions for the establishment of other plant species. They pave the way for the development of more complex and diverse plant communities as succession progresses.