Secondary succession

Secondary succession
n., [ˈsɛkənˌdɛɹi səkˈsɛʃ.ən]
Definition: re-establishment of organisms following an ecological disturbance

We all have come across news where forest lands got destroyed by wildfires. Or sometimes we have read about an entire regional flora being slashed off for the sake of an agricultural experiment but left midway. Or some other time we heard about natural calamities like cyclones, hurricanes, or turbulent windstorms destroying the local ridge areas.

Do you wonder how these lands regain their flora? Would you believe that the soil of these areas retains the magic potion to bring back the ‘green life’ as it was before the bad times stepped in…? Yes, you are right! A type of ecological succession will take place and ensure the revival of plant, microbial and entomological life!

This type of ecological succession is called “secondary succession”. Read on to learn how to define secondary succession, what causes secondary succession, when does secondary succession occur, etc.

Secondary Succession Definition

What is secondary succession? In biology, secondary succession is defined as the re-establishment or re-colonization process of a full-fledged ecological community from the remnants of the soil after an ecological disturbance. Secondary succession contrasts with primary succession in the presence of some remnant precursors of soil in secondary versus none in primary succession.

Some important pointers to secondary succession:

1. Secondary ecological succession encounters lesser fights for resources as compared to primary succession. The pioneer species in this succession process are also more privileged. Primary succession begins with a crisis of resource availability while secondary succession begins with substantial resource availability. Major plant energy resources are derived from the available remnants in the soil like decomposed organic material, inorganic salts, ions, humus, etc.
2. Both primary and secondary successions begin with pioneer species that carry out the establishment or re-establishment process of the barren or destroyed ecosystems.
3. The pioneer species of primary succession are the only plant life and blue-green algae/cyanobacteria; all being ‘photo-auto-lithotrophs’ i.e. succession producers.
4. The pioneer species in secondary succession don’t necessarily have to be photo-auto-litho-trophic.
5. Secondary succession can never occur as the first line of succession; it always follows after a primary succession has occurred and the ecosystem is again destroyed by some ecological force. So, if asked, “Is soil necessary for secondary succession?”, the answer is yes. A remnant substrate or precursor is essential for secondary succession to begin.
6. How long does secondary succession take? The answer is shorter than primary succession. Secondary succession takes nearly 50-200 years to finish. Primary succession takes longer durations (nearly 1000 years) than secondary succession.
7. Factors affecting secondary succession:
   1. Trophic interactions
   2. The initial composition of the environment
   3. Competition-colonization costs and trade-offs
   4. Seed production and dispersal rates
   5. Microclimatic conditions
      • Landscape structure
      • Habitat patch size
      • Distance to outside seed sources
      • Bulk density
      • pH
      • Soil texture or soil formation
8. Some examples of the remnants that lead to secondary succession are:
   1. Some plants and animals from the previously existing animal-plant community
   2. Soil and humus
   3. Buried seeds, roots, underground vegetative organs of plants

Ecological succession Overview

• Definition of ecological succession

Ecological succession is the process that drives the community structure changes by specifically altering the species structure from time to time. Ecological succession encompasses all the factors, processes, and interrelationships of a community governing its evolution over time. It deals with the entity called time in terms of evolutionarily relevant scale (not 1 or 2 years, but long stretches of time!).

Every physical, chemical, and the biological entity is subject to change with time and this is what ecological succession describes; how different species evolve, how the evolution of one affects the other, how co-evolution takes place, and how organisms slowly adapt to thrive in environmental harshness!!

• Types of Ecological succession

There are two types of successions.

1. Primary succession
2. Secondary succession

Some biologists like to include a third tertiary succession, too. But that is beyond the scope of this article.
Look at the table below to understand the characteristic differences between the two.

• Secondary succession versus primary succession

Data source: Akanksha Saxena of Biology Online

Secondary Succession Examples

Some examples of secondary succession include the re-establishment of a destroyed previously-existing community of flora and fauna. Such secondary succession can happen after:

• After forest fire
• After flood
• After harvesting
• After epidemic disease
• After pest attack
• After hurricane
• After a cyclone (common in tropical rain forests with fast-growing evergreen trees)
• After windstorm

Some examples of other pioneer species of secondary succession are the tree species, microbial and invertebrate taxa that can be photo/chemo, auto/hetero, and litho/organo trophs.

1. Many types of microbial species (bacteria, archaea)
2. Invertebrates taxa
3. Tree species like Betula spp.(birch tree species) & Alnus spp.(Alder tree species)
4. Boreal pine forests

• Case Study: Secondary succession Yellowstone National Park

In the year 1988, a severe drought hit the North American region leading to the initiation of unabated wildfire in the Yellowstone National Park. Almost 793,880 acres of land were reported to be burned off. Several futile attempts were made to put out the fire. No one expected the forests to survive after this misfortunate incident. But in the following spring, the Yellowstone forests rose to green abundance. This is an exceptional display of secondary succession at work!

The main factors noted for this succession were ashes, nutrient influx, and heavy precipitation in the consecutive years till 1999. Generally, the main early successional species credited for the re-establishment of the ecological system are known to develop a number of adaptive characteristics like the thick bark, well-protected seed system, insulated deep roots, etc. Only after these species revive the ecosystem, the succession of plants further takes place.

Some of the species responsible for secondary succession in the case of the Yellowstone wildfire of 1988 were:

1. Pinus contorta (lodgepole pine trees, shore pine, twisted pine, or contorta pine)
2. Pseudotsuga menziesii var. glauca (rocky mountain douglas-fir)
3. Populus tremuloides (aspen tree)

Figure 1: Left: Lodgepole pine — scientifically called the Pinus contorta — is the prime leader that helped Yellowstone National Park in recolonization after the mad fires of 1988. Image Credit: Yellowstone’s Photo Collection. Right: Rocky mountain Douglas-firs were one of the most abundant representatives of the Yellowstone National Park. They contributed a big proportion to the re-colonization process of the area after the 1988 fires. Image Credit: William W Dunmire, 1971.

• Chemical associated with re-establishment of plant species after wildfires

Study with the model plant Arabidopsis thaliana: It has been observed that forest fires act like the forest’s cleansing ritual where the old representatives of the community are replaced by the sprouting of new ones. A study by Guo et al. in 2013 (Ref. 1,2) reported that the dying plant species generate a signal (a chemical in nature) that incites the sprouting of the dormant seeds. The chemical responsible was called karrikins. This chemical was associated with the ability to push through the ashes and regenerate the ecosystem after wildfires destroyed it.

• Fire

As discussed in the Yellowstone National Park case, fire is an important factor leading to secondary succession. It can happen both ways, naturally or human-caused fire. Natural fires ensure a time-to-time renewal of the ecosystem. The practice of slash and burn agriculture is a controlled fire method used by many indigenous tribes across the world. Not only does this increase the nutrient influx and ashes in the soil, but also temporarily deplete the weed, pest, and parasitic growth in the area.

In India and some parts of Bangladesh, a local practice known as jhoom/jhum runs on this philosophy.
Changes due to fire in the ecosystem are immense. Some of them are:

• • Increase in the total moisture content of the topsoil (no plants means no transpirational loss)
  • Increase in the NPK in soil (decomposition of ashes leads to leaching of NPK- nitrogen, phosphorus, and potassium)
  • Increase in the pH of the soil (due to acid combustion)

• Harvesting, Logging, and Abandonment of Crop Land

Croplands are usually prone to soil erosion because of the poor planning of the diversity of crops. With a lack of combination of both shallow and deep-rooted plants, abandonment of croplands can render a land at high risk of erosion and washing away. This is the site where secondary succession plays a restoration role. An important point to note is that the succession in such landscapes is usually ‘slower’ as compared to succession after natural calamities. The reason for this lowered speed is the unavailability of dormant seeds and plant plants to regrow as human-cultivated croplands are highly homogenized and manipulated.

Specific changes in the harvested, logged, and abandoned lands due to secondary succession are as follows:

1. Inorganic nutrient enrichment
2. Increase in soil organic content
3. Prevention of soil erosion
4. Increase in soil porosity
5. Rehabilitation of floral species that were considered weeds or parasites
6. Rehabilitation of faunal species that were kept away from farmlands
7. Restoration of micro-habitat for several microbial, invertebrate, and insect species

Renewal after Disease

The secondary succession in disease-struck vegetation can lead to different states. They can be:

1. Regrowth of earlier species: Total wiping out of the plant diseases and healthy regrowth of the previous vegetation type happens when the seeds or under-soil vegetative parts remain dormant and undiseased.
2. Invasion by new species: Total change of the species pattern happens when even the seeds, cones, or under-soil vegetative parts of the previously occurring vegetation type are also affected. This is so because now the land will be open to invasion by new vegetation species that were previously restricted.

• Gap Dynamics

When an ecological disturbance element creates a gap in the forest canopy (a hole in between tall trees), the plant growth pattern that follows this gap formation is referred to as ‘gap dynamics’. Secondary succession is a more common process in gap dynamics than primary succession.

​Stages of Secondary Succession

Let’s now discuss the four stages of succession for secondary types of succession in this section. To begin with the first stage of succession, an incidence of a destroying force (fire, flood, volcanic eruption, agriculture, etc) has to hit the area under focus:

• Stage-1

• The rapid growth of pioneer species of secondary succession (fast-growing species like shrubs, native spreading grasses, other herbaceous plants, climbers, other low-lying species, dominant tree species like hickory forest)
  Time span: Usually first 3 years

• Stage-2

• Growth of temporary short-lived annual plant species that are again fast-growing
  Time span: Usually 10-30 years

• Stage-3

• Biomass-enriching, heliophilic tree species (non-pioneer species which are usually slower growing plants)
  Time span: 75-150 years

• Stage-4

• Shade tolerant trees develop (this climax community remain stable and last till the next ecological disturbance arrives)

Note:

• Herbaceous plants grow fast and only when enough light reaches the lower levels of the forest ecosystem. Hence, they occupy the first stage of secondary succession.
• Members of Stage-2 and Stage-3 are called intermediate species of secondary succession.
• Trees begin to enrich and re-populate the area by the end of 3rd stage.

Interesting Case of “Pyrophytic plants”

Pyrophytic plants are the type of plants that have evolutionarily evolved to tolerate fire. These plants with their existing growth aren’t negatively influenced by fire. Rather, fire helps in some or the other sustenance process of the plant. These plants have developed several adaptive mechanisms to outcompete the other plants.

Some of the adaptations of these plants are:

• Thick bark (adaptive mechanism for protection of the inner plant elements)
• Dormant reproductive cones (break dormancy and open only on exposure to cones)
• Seeds (well-protected in the resinous substance)
• Seed germination activation on fire exposure (incited by chemical signal, melting of resin, etc)
• Very deep roots (provides good insulation to roots, helps re-growth even when the above-ground parts of the plant are fully destroyed)
• Thermal insulation (via moist tissues, bark nature, stem encapsulation by a bunch of dead leaves)
• Stimulation of luxuriant blooming/flowering post-fire incidents
• Self-pruning mechanism with a tall, overhead crown (like in larger deciduous trees overtop)

Answer the quiz below to check what you have learned so far about secondary succession.

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Further Reading

• Community Patterns – Biology Online Tutorial

References

• Smoke signals: How burning plants tell seeds to rise from the ashes – Salk Institute for Biological Studies. (2013). Salk Institute for Biological Studies. https://www.salk.edu/news-release/smoke-signals-how-burning-plants-tell-seeds-to-rise-from-the-ashes/
• Guo, Y., Zheng, Z., La Clair, J. J., Chory, J., & Noel, J. P. (2013). Smoke-derived karrikin perception by the α/β-hydrolase KAI2 from Arabidopsis. Proceedings of the National Academy of Sciences of the United States of America, 110(20), 8284–8289. https://doi.org/10.1073/pnas.1306265110
• Donato, D. C., Harvey, B. J., and Turner, M. G.. 2016. Regeneration of montane forests 24 years after the 1988 Yellowstone fires: A fire-catalyzed shift in lower treelines? Ecosphere 7( 8): e01410. 10.1002/ecs2.1410
• Thrupp, A., Hecht, S., & Browder, J.O. (1997). The Diversity and Dynamics of Shifting Cultivation: Myths, Realities, and Policy Implications.
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