Ecological Succession — Definition & Diagrams

What Is Ecological Succession?

Communities often have to deal with disturbances. These events negatively affect their relationships and environment. Disturbances can be anything from a wildfire to a meteor strike. The plant and animal populations react to these disturbances with ecological succession.

It's how a community regrows after a disturbance. This is an ordered process. Protists will move in first, then plant communities begin to re-build. Moss and lichen will emerge, followed by hardy grasses and shrubs. There are two kinds of succession: primary and secondary.

What Is Primary Succession?

Primary succession occurs when some daring plant species move into areas where there is no existing community. These areas are places like sand dunes, bare rocks, the areas exposed after a glacier melts, and islands formed by volcanoes.

Who Moves In During Primary Succession?

The plants that dare to try to live in these barren areas are called pioneer species, which is a pretty fitting name. Pioneer species are protists and plants like mosses and lichens. These species will grow for a long time; breaking rocks, dying, and becoming dirt.

What Is Secondary Succession?

Secondary succession happens when part of the original community remains after the disturbance. It's faster than primary succession since part of the original community is still there. The next type of plants to move in are grasses and hardy plants like dandelions. Over time, bigger and bigger plants move in including trees and shrubs. One interesting type of plant are those termed "shade tolerant", which means that they can grow well under the shade of other, bigger trees.

The environment changes over time until a stable ecosystem is created. We call this new ecosystem a climax community. The climax community lasts for a long time, often until the next disturbance mixes things up.

What About After Secondary Succession?

In a healthy ecosystem, secondary succession can create a copy of the original community. That's to say, the climax community is just like the original community that was destroyed.

If the ecosystem isn't healthy, it may never be restored to what it once was. Human-caused disturbances play a major role in the health of the environment.

$$\color{#8925ae}{\text{Vocabulary Review:}}$$

$\color{#8925ae}{\text{Ecological Succession}}$ : How a community recovers after a disturbance

$\color{#8925ae}{\text{Pioneer Species}}$ : The first stage of succession. The first generation of plants that inhabit an area after a disturbance

$\color{#8925ae}{\text{Climax Community}}$ : The final stage of succession. A stable ecosystem exists until the next disturbance

What Is Primary Succession?

When primary succession starts, there are no plants or animals in a given space. This kind of succession can happen after a glacier passes through. Or maybe a volcano creates a lava flow, leaving behind nothing but stone. After these kinds of disturbance events, pioneer species settle on the stone. These fungi and microbes then begin to break it down.

Over time, a thin layer of soil will form. Small plants will then begin to colonize the area. As more plants and other organisms grow, reproduce, and die, the soil layer grows. When the soil layer grows, it can support larger organisms like trees. When this environment becomes a functioning ecosystem, we call it a climax community.

What Is Secondary Succession?

In secondary succession, we start with some vegetation already. In this case, a disturbance event destroys only part of an area. That's why there are some plants left behind.

Over time, the plants will grow back. Secondary succession is faster than primary succession. This is because the plants that survive give the regrowth a head start.

The two sub-types of plant succession are autogenic and allogenic. When mushrooms and small plants add organic content to soil, they cause autogenic succession. This means that plants and other organisms are the cause of change.

When animals or natural processes move plants and soil around, they cause allogenic succession. External forces in the environment cause allogenic succession.

How Plant Communities Regrow After a Disaster

When a landscape is disturbed, plants and animals may be completely gone or severely impeded in their growth. A new plant community will move in to take over the area. This can happen in many places like an area where a glacier used to be. Another example is where lava has flowed and killed all previous life.

Because the new area is free of plants, there will be no competition for new plants. However, taller plants have a hard time growing in this new environment. The soil isn't developed enough for trees to take root, and the area is too sunny for many plant seeds to survive.

Primary Successors

There are groups of plants that can survive in this environment. They will form a group called primary successors. This group of plants consists of small weeds and non-vascular plants. These plants are hardy and grow fast. They are tough and not picky with their conditions.

Secondary Successors

After primary plants have been around for a while, plants like trees can start growing. We call this second group of plants secondary successors. This group of plants out competes the smaller, quicker growing primary successors and kicks them out.

If the environment wasn't completely destroyed, secondary successors come back right away. A hurricane can disturb an environment by removing plants and knocking over trees. However, the types of plants that come back afterward are similar to those that were there before the disturbance.

(Video) Ecological Succession: Change is Good

by CrashCourse

Succession is the process through which plants take over new land after some disturbance destroys plant and animal populations.