Ecological successions: changes in biological communities
Introduction - what they are, examples
If we consult a dictionary of Portuguese to know what a succession is, we will find something like this: series of events that follow or follow in a certain order.
In this sense, ecological successions are sequential changes in both the structure and functionality of biological communities. In many cases these changes follow more or less defined patterns.
Examples of ecological successions may be the simplest, such as the appearance of grass or undergrowth on a ravine that has collapsed. But it can also be one that spans an immense area and takes a long time to complete: the sequence of events ranging from the spill of lava from a volcano on a terrain to the stage of a full forest on it.
Ecological successions have the following attributes:
- Always start after a natural disturbance or a disturbance caused by human actions;
- They can start from “zero point”, ie the first organisms to colonize space are very simple: bacteria, algae, fungi, and non-vascular plants. In this case we call it primary ecological succession;
- May start in circumstances in which a biological community already exists. In this case the succession is called secondary;
Immediately after the disturbance, whether mild or drastic, the richness of biological species is low. Most species present are those in the pioneer category;
- After a while, the species richness increases, being then composed by pioneer species, but also by those of the secondary category;
- As time goes on, species richness peaks: pioneer, secondary and climax species are found;
- Long after the disturbance has occurred, species richness declines again as some pioneer species are no longer present;
- If another disturbance occurs (fall of tall tree, burnt, tsunami, collapse), the ecological succession restarts.
In the case of open-cut forest blocks such as road, pasture or field, if one block experiences intense disturbance, the other block may assist in the ecological succession of the first block. It will be the source of seed seeds for pioneer, secondary and climax plants.