Plant community is a collection of plant species within a designated geographical unit, which forms a relatively uniform patch, distinguishable from neighbouring patches of different vegetation types. The components of each plant community are influenced by soil type, topography, climate and human disturbance. In many cases there are several soil types within a given phytocoenosis.
A forest community includes the overstory, or upper tree layer of the canopy, as well as the understory

Understory

Understory is the term for the area of a forest which grows at the lowest height level below the forest canopy. Plants in the understory consist of a mixture of seedlings and saplings of canopy trees together with understory shrubs and herbs...

, further subdivided into the shrub layer, herb layer, and sometimes also moss layer. In some cases of complex forests there is also a well-defined lower tree layer.

Examples

An example is a grassland on the northern Caucasus

Caucasus

The Caucasus, also Caucas or Caucasia , is a geopolitical region at the border of Europe and Asia, and situated between the Black and the Caspian sea...

 Steppes, where common grass species found are Festuca sulcata and Poa bulbosa

Poa

Poa is a genus of about 500 species of grasses, native to the temperate regions of both hemispheres. Common names include meadow-grass , bluegrass , tussock , and speargrass. "Poa" is Greek for fodder...

. A common sedge in this grassland phytocoenosis is Carex shreberi. Other representative forb

Forb

A forb is a herbaceous flowering plant that is not a graminoid . The term is used in biology and in vegetation ecology, especially in relation to grasslands and understory.-Etymology:...

s occurring in these steppe grasslands are Artemisia austriaca and Polygonum aviculare

Polygonum aviculare

Polygonum aviculare or Common Knotgrass is a plant related to buckwheat and dock. It is also called birdweed, pigweed and lowgrass. It is an annual found in fields and wasteland, with white flowers from June to October....

.

An example of a three tiered plant community is in Central Westland of South Island, New Zealand. These forests are the most extensive continuous reaches of podocarp/broadleaf forests in that country. The overstory includes miro

Miro

Miro may refer to:* Mojahedin of the Islamic Revolution Organization, a reformist Iranian political organization* Prumnopitys ferruginea, an evergreen coniferous tree endemic to New Zealand.* Miro Technologies, an MRO supplier from California...

, rimu

Rimu

Rimu can mean the following:*Dacrydium cupressinum, also rimu, a tree endemic to New Zealand*Rimu, Southland, a locality in Southland, New Zealand*Rimu, West Coast, a locality in the West Coast region of New Zealand...

 and mountain totara. The mid-story includes tree ferns such as Cyathea smithii

Cyathea smithii

Cyathea smithii, commonly known as the Soft Tree Fern or Katote, is a species of tree fern.-Distribution and ecology:The species natural distribution covers North Island, South Island, Stewart Island/Rakiura, and the Chatham Islands of New Zealand south to the Auckland Islands...

 and Dicksonia squarrosa, whilst the lowest tier and epiphytic

Epiphyte

An epiphyte is a plant that grows upon another plant non-parasitically or sometimes upon some other object , derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it, and is found in the temperate zone and in the...

 associates include Asplenium polyodon

Asplenium polyodon

Asplenium polyodon, commonly known as Sickle Spleenwort, is a species of fern in the family Aspleniaceae. The distribution of A. polyodon includes parts of the countries of Australia and New Zealand...

, Tmesipteris tannensis

Tmesipteris tannensis

Tmesipteris tannensis is a fern ally endemic to New Zealand. It is usually epiphytic on trees and tree ferns, but is occasionally terrestrial....

, Astelia solandri and Blechnum discolor

Blechnum discolor

Blechnum discolor is a species of fern in the family Blechnaceae. This species is endemic to New Zealand. As noted by C. Michael Hogan, this species is found in a number of forest communities in diverse locations within New Zealand, and is sometimes a dominant understory component.Spores are...

.