Succession and Seral Stages

Successional Stages

As newly formed land becomes available to terrestrial plants, it goes through a series of developmental stages. Sand dunes created along the coast go through stages to become coastal forest. Land formed around lakes starts out as water bogs before becoming meadows and forests. Each stage is called a sere.

The most important idea to remember in the succession of seres is that plants that grow well in one condition can create an environment that gives the survival edge to another plant.

For instance, Black Cottonwood tree seedlings grow well in full sunlight. When their seeds land in open meadows they grow quicker than competing trees. Eventually they form a shade canopy over smaller trees, including their own children. The second generation of Black Cottonwood seedlings is now growing in a shaded environment their own parents created. In this shaded environment, they no longer have an edge over trees that are more shade tolerant. Eventually, the trees that thrive in their own shade will succeed over the Black Cottonwoods. (Don't worry, by this time there's a new meadow somewhere else for the Black Cottonwoods to go and the cycle continues.)

Plant B succeeds Plant A when B is better adapted to the environment created by A.

Biologists have a lot of names for the beginning seres. These are the first stages of terrestrial plant takeover of newly formed land. Depending on the specifics of the situation, different plants will thrive. Some of these seres are:

(All of the images on this page come from the CalFlora Website)

Juncus lesueurii (salt rush) replaces the pioneer cordgrass after the later has built up the marsh soil of the halosere.

Photographer: Charles Webber

Halosere:

Land that is first raised out of the ocean is often waterlogged with saltwater and subjected to a lot of wind. A plant that thrives in the halosere is a halophyte.

An example of succession in a halosere is as follows: Spartina alterniflora (smooth cordgrass) is a pioneer in newly formed saltwater marshes in Texas and Louisiana. As it grows, it stabilizes the area, and by adding its own organic debris, it builds the soil up both in quality and elevation. Once it does, other Spartina species as well as saltgrass (Distichlis spp.), and rushes (Juncus spp. shown at left) can thrive often replacing the original S. alterniflora

Psammosere:

Land created by sand dunes creates a very hostile environment to which only a few plants are adapted. These plants tolerate abrasion by sand, desiccation by wind and high temperatures and the occasional dowsing with saltwater or sea spray.

While you'd think a plant suited to this environment would be called a "psammophyte" (compare halosere and halophyte), I haven't actually found that would used.

Succession in the psammosere might go as follows: Sand twitch (Agropyron junceiforme) thrives under the initial conditions of the psammosere. As it grows, its underground rhizomes stabilize the sand dune reducing ground shift and abrasion.

Marram grass (Ammophila arenaria, shown at right) can now grow more easily although it has also been know to be a pioneer plant. It stabilizes the dune more with its rhizomes.

Both species contribute organic plant matter increasing soil quality. Later grasses such as lyme grass (Elymus arenarius) come in at this point further stabilizing and improving the soil. Eventually, the land is built up and away from the sea. Protected from the higher winds and sand abrasion at the coast and containing more organic matter, the land can now support more pasture type grasses and wildflowers. Eventually, shrubs and trees will emerge.

Marram grass (Ammophila arenaria) pioneering a sand dune.

Photographer: Charles Webber


Scirpus robustus
(bull tule, alkali bulrush, big bulrush)
This kind of plant can grow partially submerged after the soil has been built up by more water adapted species.

Photographer: Brother Alfred Brousseau

Hydrosere:

Inland lakes are constantly being filled in by the silt brought down by their rivers. As the soil gets built up, it provides a new environment for different kinds of plants, starting with water plants and ending with the introduction of fully terrestial plants.

Initially, the soil is completely underwater and too deep for any plants that thrive in air. Eventually, the soil is built up to a point that some plants, such as water lillies, can grow. These plants have their roots and buds submerged, but their leaves float on the surface of the water.

When the soil is built up a little more, grass like plants, such as Scripus robustus shown at left, begin growing. At this point organic matter from the plants themselves contributes to soil build up. Swamp and then coarse grassland develops as the soil is raised and drained.

Other Primary Situations: 

These are just some of the beginning stages. Other primary situations might be from lava flow, severe fire, and the ubiquitous "human interference". In all of these situations there will be some local species that are really good at taking over the newly cleared land.

In the Pacific Northwest, Epilobium angustifolium (shown at right) has the common name, "fireweed" because it's just so good at coming back to places recently destroyed by fire. In fact the north face of Mount Saint Helen's is already home to a lot of the stuff. In Hawaii there are many plants that readily invade each new layer of rich volcanic soil Mauna Loa lays down. All of these plants are considered pioneer plants.

 
The fireweed in this picture is coming back to an area recently denuded by fire.

Photographer: Charles Webber

Grindelia stricta (Puget Sound gumweed) is a mesophyte that comes into marshlands after they've been developed by halosere pioneer plants.

Photographer: Gladys Lucille Smith

 

What Happens Next:

While some pioneer plants are adapted to many environments and therefore stick around through various seres, many are more narrowly adapted. These plants only thrive in a small range of environments near the beginning of succession.

They are quickly replaced by "mesophytes" or midrange plants that have developed adaptions appropriate to the kinds of environments created in the middle stages of succession. There are so many possibilities for the middle seres that they are often just named for the dominant species.

The Final Chapter? Not Likely! 

It would be a mistake to think of the climax stage as the "goal" of the preceding stages. The only goal a plant has is to reproduce and no Black Cottonwood grows with the intention of creating a shade canopy for other, later stage trees.

The changes in environments and the related changes in plant selection occur as natural consequences of other processes. The cottonwood grows in order to produce seed and make more cottonwoods. It's just a consequence of it's own growth that it puts its children out of the running in that particular area.

Eventually, however, plant communities arise creating environments that they are well suited to. If left undisturbed, these communities will recreate themselves generation after generation. This stage is called the climax and it is generally considered to be the natural conclusion to the preceding seres. In real life however, a climax might be reached several times as an area is disturbed by fire and other natural and not so natural occurances.

 

Douglas Fir (Pseudotsuga menziesii) is one the premier climax species in California.

Photographer: Charles Webber

Tree Profiles|What Is A Tree?|Glossary|Succession Status

Home|Library|Cats|Tarot|Forest|Warrior|Pagan|Email