My first association with any 'x' is the female chromosome. But that's an abstract association: the shape of the female chromosome is 'X'. I suppose that might be a legitimate blog post for today's letter, but let us venture into a word that does begin with 'x': xēros. Then we will slide right into another word that descends from xēros: xerosere.
The etymology of 'xero' is from the Greek xēros, which means 'dry'. In combination with a noun or vowel , xero- indicates dryness. Now, if we add the suffix sere, we have 'xerosere'.
Sere is derived from the modern word 'series', which means a group or a number of related or similar things or events arranged or occurring in temporal, spatial, or other order or succession or sequence. The two words were combined as xerosere in the late 1920's to refer to the series of changes occurring in the ecological succession on dry soil, including bare rock.
A primary component of a xerosere is limited water availability. Deserts, rocky places, and lava beds are examples of the type of ecological succession that typifies a xerosere.
This begins on exposed parent rocks or dry sand. The pioneer plants in the primary succession are lichens and mosses which help in forming soil by accelerating erosion. In time, herbaceous vegetation such as grasses, etc., grow on the soils deposited on rocks and enhance weathering. As these plants die, they add nutrients and organic matter to the forming soil deposited on and around the rocky areas.
Mixed shrubs then establish the area, which attracts birds and mammals. These animals help in the succession by dispersing and depositing seed. Intermediate plants develop and form a transition community. Eventually a climax community (also called a 'biome') establishes itself where populations of plants or animals remain stable and exist in balance with each other and their environment.
The following is an example of forest xerosere on barren rock.
- Bare rock is first colonized by lichens and bacteria.
- Small amount of soil formed by the lichens is colonized by mosses, which do not have roots and require little soil, and ferns.
- As the seedless plants live and die, the soil continues to develop to the point that grasses can successfully grow and a grassland community forms.
- Over time, the soil level increases to the point that shrubs can grow in the grassland.
- The grassland is replaced by a shrub community.
- The shrub community may be gradually be replaced by a forest.