How Does Hydrarch Succession Shape Aquatic Ecosystems?
Succession is a unidirectional series of changes that brings about a change in community composition. As the succession progresses, it leads to the formation of a stable climax community. The transient stages in the progressive successional series are called the seral stages. Hydrarch succession is a primary type of succession which starts in aquatic environments like ponds and lakes.
Succession in the pond or lake starts with the settlement of a pioneer community like the phytoplankton, and that leads to the formation of the forest. Major examples of hydrarch succession can be observed in the Big Islands of Hawaii as this area is prone to volcanic eruption. As the lava flows in nearby regions, new rocks are formed, modifying the soil profile in the region. This leads to new flora and fauna development.
Types of Succession
Primary Succession: The succession occurs in barren or new areas where no species existed before. Example- new volcanic island.
Secondary Succession: It occurs in the region where the developed community has been eradicated by natural forces like flood, fire, or flooding. Example- forest destroyed by fire.
Autogenic Succession: It is a self-powered succession that occurs due to the interaction of organisms with the environment. Example- primary succession.
Allogenic Succession: The succession resulting from the variation in habitat due to external agencies is allogenic succession.
Autotrophic Succession: Succession in which plants are in greater quantity than animals, occuring in an inorganic-rich environment is known as autotrophic succession.
Heterotrophic Succession: In the initial stages, animals and fungi outpower the plant. This occurs in an organic-rich environment.
Progressive Succession: In this kind of succession, simple forms get transformed into complex forms by a series of sequential changes. Example: grassland converted to forest.
Stages of Hydrarch Succession
Hydrarch succession occurs gradually and includes stages of community formation. The sequence of events in hydrarch succession is explained below:
Phytoplankton Stage: This is the primary stage of hydrarch succession. In this stage, the quality of pond water is inferior in nutrients and does not support larger life forms. Simple organisms like bacteria, algae, phytoplankton, and zooplanktons form the first seral community of the hydrarch succession. They are called pioneer communities.
These organisms proliferate and perform several metabolic activities. In this process populations of simple life forms die, and decomposers begin to multiply bringing about decomposition, and enriching the pond with nutrients. The dead organism settles at the base of the pond to form a layer called a muck.
Submerged Stage: The loose muddy layer at the base of the pond is enriched with nutrients. This layer supports the growth of rooted hydrophytes like Hydrilla, Utricularia, Vallisneria, and Ceratophyllum. These plants emerge at the depth of about 10 feet or more. When these plants die they get buried at the base of the pond, which gradually raises the surface of the pond. This stratification process results in the growth of other plants.
Floating Stage: As the name suggests, the floating plants are the new inhabitants. The depth of the water now reaches about 4 to 8 feet. The broad leaves of floating plants obstruct the light rays to penetrate the water. This leads to the death of submerged plants that colonised the pond earlier. The death of submerged plants along with the evaporation of water and silt deposition from the nearby region makes the pons shallower. Examples of plants found in this stage are Trapa, Pistia, Nymphaea, Limnanthemum, etc.
Reed-Swamp Stage: As the depth of pond water gradually decreases the floating plants get replaced by amphibious plants. The prominent examples of such plants are Typha, Sagittaria, and Phragmites. The leafage of such plants cuts off the sunlight reaching the floating or submerged plants. This leads to death resulting in the deposition, thereby reducing the depth of water. The existing plant species have well-developed root systems and form densely wooded areas.
Sedge Meadow Stage: The stratification process results in the formation of marshy habitat. Plants species like Cyperaceae and Gramineae take over the vegetation. They form dense mat-like vegetation with the help of their creepy rootstock. As the depth gradually decreases, the muddy layer gets well exposed to the air resulting in rampant loss of water. Thus marshy condition gets replaced by mesic vegetation. At the end of this stage, soil loses water and becomes dry. The soil now gets dependent on rainfall and other climatic factors.
Woodland Stage: In this stage, shrubs and, later on, woody trees appear on land. The pioneers of this stage are Salix, Cornus, Alnus, etc. In this stage, the soil gets flourished with humus with abundant microflora. Thus soil gets mineralised, favouring the entrance of new species of plants. This stage leads to the final climax stage.
Climax Stage: Finally, the hydrosere leads to the evolution of climax vegetation. The level of the soil is raised, and the soil gets enriched with humus and other minerals. This habitat favours the growth of a well-adapted, reproductive stable plant community. All types of plants ranging from herbs to tall woody trees, are seen in the climax region. The dominant woody trees control the entire foliage. Thus, a stable, balanced climate-dependent climax community evolves.
The Stages in Hydrosere
Xerarch Succession
The type of succession that begins in drier areas is called xerosere. The two seral stages are:
Lithosere: Succession occurs on barren rocks
Psammosere: Succession occurs in the sandy region
Differences between Hydrarch and Xerarch Succession
Interesting Facts
In southern Alaska, Glacier bay is one of the prominent examples of Primary Succession.
Due to global warming glaciers melted, and soon pioneer communities (Epilobium latifolium) and the mountain avens (Dryas octopetala) occupied the region.
These plants fixed nitrogen and modified the soil. Gradually taller shrubs, Sitka spruce (Picea sitchensis), western hemlock (Tsuga heterophylla), and mountain hemlock (T. mertensiana) became the dominant species of the region.
Important Questions
What are the pioneer species of hydrarch and xerarch succession?
Ans: Pioneers species of hydrarch succession are phytoplanktons. They grow independently in sunlight and are referred to as microalgae. In Xerarch Succession the pioneer community is lichen. Lichen is a symbiotic association of algae and fungi.
What are examples of secondary succession?
Ans: Secondary succession is a type where already living forms existed but natural calamities have destroyed the region. The classic example of secondary succession is oak and hickory forests, where wildfires are common. The wildfires destroy the flora and fauna. The nutrient is replenished in the form of ash which is used later for secondary succession.
Key Features
Max Witynski defines ecological succession as a gradual process that replaces species and habitats.
Hydrarch succession starts in moist places with phytoplankton as pioneer communities.
Xerarch succession starts in drier areas like sandy places or weathered abandoned rocks. The pioneer of this succession is lichens which gradually following various seral stages get transformed into woody foliage.
FAQs on Hydrarch Succession: Stages, Examples, and Importance
1. What is hydrarch succession as per the Class 12 syllabus?
Hydrarch succession is a type of primary ecological succession that begins in an aquatic environment, or hydric conditions, such as a pond, lake, or marsh. It involves a progressive series of changes in the plant communities over time, gradually converting the aquatic habitat into a terrestrial one, eventually leading to a stable mesic (moderate moisture) forest community.
2. What are the key stages of hydrarch succession in a pond?
Hydrarch succession progresses through several distinct stages, transforming a water body into a land ecosystem:
- Phytoplankton Stage: The process begins with microscopic, free-floating algae (phytoplankton) as the pioneer species.
- Submerged Stage: As the pond becomes enriched with nutrients, rooted submerged plants like Hydrilla and Vallisneria appear.
- Floating Stage: Rooted plants with floating leaves, such as lotus and water lilies, start to grow, further trapping sediment.
- Reed-Swamp Stage: Amphibious plants like Typha (cattails) and Phragmites (reeds) colonise the shallow areas, accelerating soil buildup.
- Sedge-Meadow Stage: Sedges and grasses take over as the soil becomes more solid and marshy.
- Woodland Stage: Water-tolerant shrubs and small trees appear, shading out the sedges and further drying the soil.
- Climax Forest Stage: A stable, self-perpetuating forest community, dominated by large trees adapted to the regional climate, establishes itself as the final stage.
3. How does hydrarch succession differ from xerarch succession?
The primary difference lies in their starting environments. Hydrarch succession begins in wet, aquatic (hydric) areas and progresses towards mesic conditions. In contrast, xerarch succession starts in dry, barren (xeric) areas, like bare rock or sand, and also progresses towards a stable mesic community. Both ultimately aim for a climax community, but their pioneer species and intermediate stages are completely different due to the initial availability of water. You can learn more in these Revision Notes on Ecosystem.
4. What are pioneer species in hydrarch succession and why are they important?
The pioneer species in hydrarch succession are typically microscopic autotrophs like phytoplankton (e.g., diatoms, green algae). Their importance is foundational; they are the first organisms to colonise the nutrient-poor water. Through their life cycles of growth, death, and decomposition, they add organic matter and nutrients to the water body, creating a base layer of sediment. This enrichment makes the environment suitable for the next stage of more complex, submerged plants to grow, thereby initiating the entire successional sequence. These concepts are crucial for Class 12 Biology Chapter 12 Important Questions.
5. Why is ecological succession, like hydrarch succession, considered a unidirectional process?
Ecological succession is considered unidirectional because it follows a predictable path from simple, less stable communities (pioneer species) to complex, more stable communities (climax community). Each successive community modifies the environment (e.g., by creating soil, increasing humidity, providing shade), making it less favourable for itself but more suitable for the next community in the sequence. This directional change, driven by the organisms themselves, rarely reverses under natural conditions, always moving towards a state of greater biomass, biodiversity, and ecological stability.
6. What determines the climax community in a hydrarch succession?
The climax community in a hydrarch succession is primarily determined by the regional climate. While the process starts in water, it culminates in a terrestrial ecosystem whose final, stable state depends on factors like average temperature, rainfall, and soil type of the geographical area. For example, in a region with high rainfall and moderate temperatures, the climax community will likely be a temperate forest. It is a state of equilibrium where the vegetation is in balance with the local environment.
7. What is the ecological significance of hydrarch succession?
The ecological significance of hydrarch succession is immense as it is a natural process of ecosystem creation. It demonstrates how life can transform a sterile aquatic environment into a highly productive and biodiverse terrestrial ecosystem, such as a forest. This process creates new habitats for a wide range of organisms, contributes to soil formation, and plays a crucial role in the nutrient cycling and energy flow of a region, showcasing the dynamic and resilient nature of ecosystems.
