Sere is used in two different senses in the field of ecology. It may be used to refer to the the complete sequence of ecological communities, from the initial state to the climax community, within a given area. It may also be used to refer to one stage within this sequence, in which case the term seral community may also be used.

Seral stages include:

This is known as sereal succession.

From seral we get other weird words, like:
Subsere: a secondary series of ecological communities resulting from comparatively minor ecological disruptions, such as fire or the introduction of a new species.
Hydrosere: an sere in an aquatic habitat.
Xerosere: a sere in a dry environment (desert).
Lithosere: a sere in a rocky environment (mountains).
Psammosere: a sere in a sandy environment (sand dunes).
Halosere: a sere in a salt-water environment (usually applied to salt marshes.