SUCCESSION

1. Introduction
2. Types of succession
3. Examples of Succession
4. Making sense of succession
• Facilitation, inhibition, tolerance
• Climax theories
5. Stages of Forest Recovery
6. Disturbance

INTRODUCTION

Succession: Non-seasonal change in species composition as a function of time, usually following disturbance. (contrast with glossary definition)

Although it is defined in terms of species composition, succession is always accompanied by changes in the environment (soil depth, soil nutrients, light characteristics, fuel characteristics, etc.).

Succession is often directional, and sometimes predictable.

Sere: A series of successional stages (equivalently, a continuum with time as the environmental gradient).

Seral stage (successional stage): recognizable types of communities during succession. For example, annual herb, perennial herb, shrub, forest. Stages do not need to be distinct.

TYPES OF SUCCESSION

autotrophic vs. heterotrophic

Autotrophic succession: Succession in which most of the organic matter is fixed by autotrophs; most living biomass is in plants.

Heterotrophic (Degradative) succession: Succession on a degradable source; most living biomass is animal, fungal, or microbial material.

primary vs. secondary

Primary succession (glossary): sequence of communities developing in a newly exposed habitat devoid of life (eg. succession on bare rock, newly deposited sand).

Secondary succession (different from glossary): sequence of communities taking place on sites that have already supported life (eg. oldfield succession, clearcut forests, burned areas, etc.).

Perhaps the most useful distinction between primary and secondary succession is that the latter originates with soil.

EXAMPLES OF SUCCESSION

• Glacier Bay, Alaska: pioneer species -> willow -> alder -> spruce -> hemlock/spruce
• North Carolina Piedmont: crops -> horseweed -> aster/goldenrod -> pines -> oak forest
• Lake filling in upper Midwest: sedge mat -> shrub zone -> hydric forest -> mesic forest
• Utah Mountains: talus slope -> spruce-fir -> tall-shrub -> upland herbs
• Cyclic succession

STUDY TABLE 22-2: Characteristics of plants during early and late succession

Succession rarely follows precise pathways.

CONNELL AND SLATYER'S THREE MECHANISMS OF SUCCESSION

1. Facilitation: The organisms at a given successional stage make the environment more suitable for later successional stages. Examples: lichens breaking down rock into soil, nitrogen-fixing plants improve fertility of soil, nurse plants
2. Tolerance: The organisms of a given successional stage have little impact on later successional stages. Example: Oldfield succession (possibly)- species of all stages get started at the same time, but are dominant at different times because of different life histories.
   
3. Inhibition: The organisms at a given stage resist invasion by organisms of later stages. Succession proceeds when the individuals of a given stage die. Example: allelopathy
   

 

CLIMAX

Climax (in glossary): the end point of a successional sequence, or sere; a community that has reached a steady state under a particular set of environmental conditions.

CLIMAX THEORIES

• Monoclimax theory (Clements): all vegetation within a region will converge to the same vegetation type, which is regulated by homeostasis.
• Polyclimax theory (Tansley): there are a number of types of climax within a region, each of which reflects a different soil type, local climate, etc.
• Climax-Pattern theory (Whittaker): Succession will result in a continuum of climax types, varying along environmental gradients.
• Nonequilibrium hypotheses: Climax rarely, if ever, occurs; change is continual. History and random events are important. Even if equilibrium is theoretically possible, disturbance is too frequent to allow it.

Shifting mosaic steady state: Although the vast majority of sites in a landscape are changing (recovering from disturbance), the landscape may be in a steady state. This is because there is, through time, a reasonably constant portion of the landscape in each successional stage. A shifting mosaic steady state is a special case of a Dynamic Equilibrium.

The disturbance regime (discussed later) must be constant for this to hold.

This allows the evolution of disturbance specialists (many of which have become weeds).

STAGES OF FOREST RECOVERY

Although a steady state or equilibrium may exist for total biomass, this does not necessarily hold for species composition.

DISTURBANCE

Disturbance: an abrupt event that removes individual organisms or biomass and opens up space (or frees resources) which can be exploited by other organisms.

Disturbances vary in spatial scale, intensity, frequency, and type.

 

Disturbance regime: The sum total of all the kinds of disturbance expected to occur in a region, along with the frequency and spatial scale of each kind.

patch: that area of ground which is disturbed

return interval (turnover time): The average amount of time between disturbance events for a given patch

The study of organism's response to the disturbance regime is called patch dynamics, which views communities as open systems, with potential for immigration and extinction.  Patch dynamics is important in land management. 

This page was created and is maintained by Mike Palmer.

carex@okstate.edu
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