Xerarch Succession

Xerarch Succession is the natural process of plant succession in dry conditions. “Xero” signifies “Dry”. Xerarch succession example involves the colonization of plant communities on a barren sand dune, where pioneer species like lichens gradually give way to grasses, and eventually trees, establishing a stable climax community.

Xerarch succession goes through various stages including crustose lichen stage, moss stage, and others to finally reach the forest or climax stage. Xerarch succession is of two types – lithosere succession and Psammosere succession. In this article, we will learn about the xerarch succession, its types, and significance.

The natural process of plant succession in dry or arid conditions, such as deserts and dunes, is known as xerarch succession. It comprises the gradual colonization and replacement of plant species over time, fueled by interactions between biotic and abiotic elements such as soil properties, climate, and water availability. The term “xerosere” describes the sequence of ecological communities that initially develop in extremely arid habitats, such as rocky deserts, or on unweathered rock surfaces during the initial stages of xerosere succession.

Pioneer species like lichens and mosses are plants that can tolerate drought. They colonize barren substrates in xerarch succession and gradually foster the emergence of more complex plant communities. This process ultimately results in the development of stable ecosystems that are suited to arid environments.

There are two major Xerarch succession types:

Lithosere Succession

• Lithosere succession occurs on bare rock surfaces where no soil is present.
• Pioneer species like lichens and mosses colonize the rock surface, breaking down rock material and creating soil over time.
• As soil accumulates, more complex plants such as grasses, herbs, and eventually shrubs and trees, establish and diversify the plant community.
• Over centuries, the lithosere succession leads to the formation of a stable and mature ecosystem on the rocky substrate.

Psammosere Succession

• Psammosere succession is a type of ecological succession that occurs in sand dune habitats.
• It begins with the colonization of pioneer species like grasses and lichens that can tolerate harsh, sandy conditions.
• Over time, as soil accumulates and stabilizes, more complex plant species such as shrubs and trees establish, altering the dune ecosystem.
• Psammosere succession plays a vital role in stabilizing and diversifying sand dune habitats, providing habitats for various plant and animal species.

The diagram of xerarch succession is given below:

The first organisms that colonize on empty surfaces in arid area are known as pioneer species in xerarch succession. These pioneer species have certain traits.

• Drought Tolerance: Pioneer species have developed defenses against severe droughts such as water-saving techniques and the ability to resist intense heat.
• Fast Reproduction: These species can swiftly colonize and establish colonies in resilient habitats with little competition since they have high rates of reproduction.
• Shallow Root Systems: Pioneer plants can use unique root structures to obtain water trapped in stony soils, or they can have shallow root systems to take advantage of moisture close to the surface.
• Smaller height: A large number of pioneer plants have prostrate or low-growing forms that reduce water loss and wind exposure that desiccates them.

Herbaceous and shrub species start to proliferate in the natural environment during the intermediate phases of xerarch succession, which helps in the formation of more complex plant communities.

• Herbaceous Species: Plants that are resistant of drought and have soft stems and non-woody features help them become established in the environment. These plants can effectively utilize available moisture and nutrients since they frequently develop quickly and have shallow root systems.
• Shrub Species: Shrubs play a significant role in the vegetation mosaic due to their deeper root systems and woody stems. In addition to offering more structural complexity, these plants provide as food supplies and habitats for a wide range of organisms.

A stable and diversified community is established when woody plants and perennial grasses take up residence in the xerarch succession.

• Woody Plants: Trees and shrubs that withstand drought, distinguished by their extensive root systems and evergreen foliage, become established members of the ecosystem. Numerous animals find structure, shade, and habitat from these woody species.
• Perennial grasses: Deep-rooted perennial grasses are essential for preserving ground cover, lowering soil erosion, and stabilizing the soil. Their vast root systems improve water infiltration and soil structure, strengthening the resilience of the environment.

There are different stages of xerarch succession which includes:

Crustose Lichen Stage

• The first stage of the colonization of bare rock by crustose lichens such as Rhizocorpon and Lecanora, which are tolerant high temperatures, little organic matter, and wetness.
• Their carbonic acid weathers the rock, setting it up for next stages, while wind and water distribute them via soredia and spores.

Foliage Lichen Stage

• Under ideal circumstances, lichens that resemble leaves, such as Parmelia and Dermatocarpon, can grow.
• These lichens are distinguished by their enormous structures, which can store water and gather dust, which helps the substrate develop.
• They produce soil formation and habitat modification by raising soil acidity and humus deposition, which shade crustose lichens and slow down their development.

Moss Stage

• The moss stage is when xerophytic mosses like Polytrichum, Tortula, and Grimmia develop themselves.
• They do this by penetrating deeply into rocky soil, where they compete with lichens for water and nutrients.
• As mosses break down, they produce a thick mat that improves soil water retention. This fosters the growth of herbaceous plants, and lessens xeric conditions in the emerging habitat.

Herbaceous Plant Stage

• Heavy moss growth contributes humus and mineral deposits to the soil, improving its ability to hold water and serving as a substrate for dust particles to settle on in the wind.
• Perennials and biennials follow annual herbaceous plants in terms of establishment, which speeds up weathering processes and lowers temperatures through transpiration.
• A few xerophytic grass species, as well as bacteria, fungi, and animals, may all flourish at this period.

Shrub Stage

• Shrubs like Phytocarpus thrive in areas with significant soil deposition because they may grow thickly and move, casting shadows over herbaceous plants.
• Their extensive roots promote soil enrichment and create wide fractures in the rock which help in the continuous development of soil.

Forest or Climax Stage

• Since humus from decomposing bushes nourishes the soil, trees are more likely to thrive than shrubs and other plants.
• Woody plants with deep roots predominate and produce shadows that prevent understory vegetation from growing.
• Unless disturbed this stable stage remains unchanged and forms a canopy of plants that include Ficus, Woodfordia, Eugenia, Sterculia, and Terminalia.
• These climate-regulated climax ecosystems are good examples of plant xerarch succession.

Also Read: Difference Between Herbs And Shrubs

In summary, xerarch succession, which is defined by the successive colonization and replacement of plant species throughout time, is an important process of ecological evolution in arid settings. Xerarch succession converts arid landscapes into a variety of stable ecosystems, starting with the first colonization by crustose lichens and ending with the emergence of climax forests dominated by woody flora. Every step of succession contributes to soil formation, habitat construction, and enhanced biodiversity, from the lichen and moss pioneering efforts to the emergence of herbaceous and shrub communities.

Also Read:

• Ecological Succession – Definition, Types, Characteristics, Causes
• Difference Between Primary And Secondary Succession
• Ecosystem Notes Class 12 Biology Chapter 12
• What are the Consequences of Deforestation?

What is Xerarch Succession?

Xerarch succession is the process of ecological succession that occurs in dry or arid environments, starting with pioneer species like lichens and mosses and progressing towards more complex vegetation over time.

Is Xerosere a Primary Succession?

Yes, xerosere is a type of primary succession, as it begins in areas where no soil or organic matter is present, such as bare rock or sand dunes.

What is the Difference Between Hydrarch and Xerarch Succession?

Hydrarch succession occurs in aquatic environments, while xerarch succession occurs in terrestrial environments, each involving different plant and soil interactions and adaptations to water availability.

What is the Correct Sequence of Xerarch Succession?

The correct sequence of xerarch succession is from crustose lichens to mosses, herbaceous plants, shrubs, and finally, climax forest.

What are Two Examples of Xerarch Succession?

Two examples of xerarch succession are the colonization of bare rock by lichens and the development of grasslands into forests.

Which Stage Comes First in Xerarch Succession?

The first stage in xerarch succession is the colonization of bare substrates by crustose lichens.

What does Xerarch Succession Lead to?

Xerarch succession leads to the establishment of climax communities dominated by woody vegetation.

What is the Climax Community of Xerarch?

The climax community of xerarch succession is a stable forest ecosystem dominated by woody plants.