The Classical Concept of Succession

A. Definition:

The replacement of the biota of an area by one of a different nature. Closely related to the concept of understory tolerance.

B. Cause of succession:

Major changes in the composition of a community can only follow changes in the environment.

Two ways the environment can change:

1. Caused by the organisms living there: Autogenic Succession
*Increasing shade, litter accumulation, temperature and humidity modifies, and differences in nutrient availability*

2. Physical changes in environment: Allogenic Succession

"Disturbances"= Natural Processes: e.g. landslides, drought, fire, flooding, grazing, hurricanes, and insect attack.

Disturbance (definition): Mechanisms which limit plant biomass by causing its partial or total destruction.

C. Stabilization and Climate

1. Succession proceeds from less stable to more stable communities.

Early successional community ----------------------> Late successional community

Successional Stages (Sere; Community Type)

• Clear-cut
• Grasses and shrubs
• Intolerant trees
• Mid-tolerant species
• Tolerant and mid-tolerant species
• Tolerant species (self-perpetuating)

2. Succession eventually terminates

In a complex of species so adjusted to each other and the environment that a condition of dynamic equilibrium or steady state is reached. Barring any disturbance or climatic change, the community may continue indefinitely.

Late successional community = Climax vegetative type

3. Late successional vegetation in the field: Individuals lost are replaced by their own progeny

D. General Trends During Succession

1. Species enrichment
2. Increased cover and biomass
3. Increased structural complexity
4. Competitive replacement

E. Types of Succession

Two broad categories of succession:

1. Primary Succession: on newly formed land surfaces not previously vegetated. Examples: lava flows, glacial retreat, bog fill-in, sand dunes, and rock outcrops.

Generally divided into:

Hydrach: on wet substrates
Xeraih: on dry substrates

2. Secondary Succession: on land that has been recently vegetated, but the vegetation has been destroyed. Examples: abandoned crop lands, fire, logging, windthrow.

F. Classical Concept:

Succession was traditionally thought to be directional, highly predictable, and repeatable: All communities eventually lead to the climax community.

F. E. Clements: original authority on plant succession (early 1900's)

"Organismic Theory", likened succession to the birth, growth, maturity and death of an organism.

Back To Main FW302 Page!