Ecological Succession Notes

Chapter VII. Ecological Succession

A. Types of Succession (based on Origin)

• Primary Succession:
  • The process of creating life in an area where no life previously existed.
  • A step-by-step invasion of animals and plants in a bare area until it becomes a climax community.
  • Begins in a place without any soil, such as:
    • Sides of volcanoes
    • Landslides
    • Flooded areas
  • Starts with the arrival of pioneer species that do not need soil to survive (e.g., lichens).
  • Overview of Primary Succession:
    • Bare rock is colonized by pioneer species (e.g., moss).
    • Decomposition creates a layer of topsoil.
    • Grasses grow and displace the pioneer species.
    • More nutrients in the soil allow for shrub growth.
    • Increase in soil depth allows for the growth of trees.
  • When lichens die, they decompose, adding a small amount of organic matter to the rock or soil, allowing mosses and ferns to grow on the new soil.
  • When mosses and ferns die, they add more organic material to the soil, thickening the soil layer, which allows grasses and other plants to take over.
  • When grasses and other annuals die, they add more nutrients to the soil, enabling shrubs and trees to survive.
  • Insects, small birds, and mammals begin to move in.
  • Types of Primary Succession (based on substrate):
    • Hydrarch: Starts on a wet substrate.
      • Hydrosere: Stages of Hydrarch Succession
        • (1) Newly formed water body
        • (2) Phytoplankton Stage
        • (3) Rooted Submerged Stage
        • (4) Rooted Floating Stage
        • (5) Reed-Swamp Stage
        • (6) Sedge Marsh or Meadow Stage
        • (7) Woodland Stage
        • (8) Forest Stage
    • Xerarch: Starts on a dry surface, like an exposed rock.
      • Stages of Xerarch Succession:
        • Bare rock
        • Lichens
        • Small annuals
        • Perennial plants, lichens, herbs, grasses
        • Grasses, shrubs, shade-intolerant trees
        • Shade-tolerant trees
        • Intermediate stages
        • Climax community
  • Example: During primary succession on lava in Maui, Hawaii, succulent plants are pioneer species.
• Secondary Succession:
  • The process of re-stabilization that follows a disturbance in an area where life has previously existed.
  • Occurs in an area or gap disturbed (by fire, typhoon, flood, and other natural or human disturbances) and previously vegetated.
  • Stages of Secondary Succession:
    • Pioneer Species: Annual plants (0 years)
    • Intermediate Species: Grasses and perennials (1-2 years), Grasses, shrubs, pines, young oak and hickory (3-4 years)
    • Climax Community: Mature oak and hickory forest (150+ years)

B. Other Types of Succession

• Cyclic:
  • When climax plant communities absorb random occurrences of gaps triggered by the fall of dead old trees, landslips, lightning strikes, etc.
  • The situation recruits light-demanding plant species that would again close the gap.
  • Never attains climax.
• Directional:
  • Linear, step-by-step invasion of plant species until a climax community is reached.
  • Sere.
• Autogenic:
  • Refers to the influence of resident plant communities (indigenous) on the limiting factors (light regime, litter, temperature oscillations, increased humidity, change in soil substrate, etc.).
  • Resident plants define the set of recruits for the next seral plant community that would emerge.
• Allogenic:
  • Succession caused by major environmental changes beyond the control of the indigenous organisms.
  • Examples include climate change, changes in sea level or topography, and bioinvasive alien species.
• Progressive:
  • Succession often leads to communities with greater complexity and progressively becoming more mesic (moist).
  • Example: Sierra Madre Mountain Ranges and other Tropical Rainforests (TRFs)
  • Pioneer trees -> secondary forest -> climax forest
• Retrogressive:
  • Opposite direction toward simpler, more depauperate communities and toward a more hydric (wet) or a more xeric (dry) habitat.
  • Some retrogressive successions are allogenic (e.g., logging, introduction of cattle, weedy annuals, and fire).

Ecological Succession

• Ecological succession is the change in species composition of an ecosystem.
• It is a series of progressive changes in the species that make up a community over time.
• Plant succession is a directional, cumulative change in the species that occupy a given area.
• Time involved: 1-500 years.

Seral Community

• A step-by-step invasion of animals and plants in a bare area until it becomes a climax community.
• Types of Seres:
  • Hydrosere: Succession in an aquatic habitat.
  • Xerosere: Succession in a dry habitat.
  • Lithosere: Succession on a bare rock surface.
  • Psammosere: Succession initiating on sandy areas.
  • Halosere: Succession starting in saline soil or water.
  • Senile: Succession of microorganisms on dead matter.
  • Eosere: Development of vegetation in an era.
• A seral community is an intermediate stage of ecological succession advancing towards the climax community.
• It is replaced by the subsequent community.
• It consists of simple food webs and food chains.
• It exhibits a very low degree of diversity.
• The individuals are less in number, and the nutrients are also less.

Climax Community

• Remains the same throughout time if not disturbed.
• Vegetation has fully developed.
• Received the maximum number of species.
• Has filled all available niches.
• State of equilibrium.
• A climax community is not limited to a tree community but can be cacti in deserts or grasses in fields.

Disclimax

• When succession is not allowed to develop due to many destabilizing factors.
• Naturally driven by external perturbations:
  • Recurrent landslides, unpredictable dry conditions, fire.
• Anthropogenic factors:
  • Farming (e.g., savanna grassland of Carranglan, Nueva Ecija).

Formation of Gaps in the Forest

• Chablis:
  • Creation of opening or gap mainly by the fall of trees.
  • Small but the most largely occurring creator of forest gaps.
  • Domino effect (fungal attack, then soon die and fall).
  • From medieval French, means fallen tree, its rests and caused light gap; vertical and horizontal projection.
• Windthrow: Hastened due to typhoon.
• Faults and Landslips:
  • Geologically unstable areas (slopes) + earthquake + rain.
  • Example: Digdig, Carranglan, Nueva Ecija, after the 1990 Earthquake; Landslide caused by typhoon Pablo in 2012.
• Volcanic Eruption: Large gaps.
  • Krakatau island in Indonesia in 1883 (completely burned to ashes) ~ recovered 34 years later.
  • Mount Pinatubo eruption (start another cycle of succession).
• Fire:
  • Regular and highly seasonal (i.e., savanna and steppes).
  • Lightning ignites dry grass and then spreads.
  • Kalimantan, Indonesia (El Nino phenomenon burned a considerable extent of TRF in Borneo).
• Anthropogenic Gaps: Worst cause of gaps!
  • Logging
  • Kaingin (slash-and-burn farming)
  • Road construction
  • Accidental fires (El Nino + accidental spread of fire).

Succession Process

1. Nudation: The exposure of a new surface in a primary succession or the clearing away of previous vegetation in secondary succession.
2. Migration: Of seeds, spores, or vegetative propagules from adjacent areas, though in secondary succession, many of these are already present in the soil (also animals).
3. Ecesis: The germination, early growth, and establishment of plants.
4. Competition: Among the established plants.
5. Reaction: The autogenic effects of plants on the habitat.
6. Stabilization: The climax.

Threats to Succession

• The grasses that move in as pioneer species are often thought of as weeds.
• The subsequent growth of shrubs is considered undesirable “brush”.

Does Ecological Succession Ever Stop?

• Over a long period, the climate conditions of an ecosystem are bound to change.
• No ecosystem has existed or will remain unchanged over a Geological Time Scale.

Schrödinger Ratio and Succession

• $\frac{CO<em>2}{O</em>2} < 1$ or $\frac{CO<em>2}{O</em>2} > 1$
• $\frac{CO<em>2}{O</em>2} = 1$ and $O<em>2 > CO</em>2$
• O2 emission: measures the rate of photosynthesis: GPP
• CO2 emission: measure of CRs or (Rs)
• 1st law of Thermodynamics: $GPP = CSB + CRs$
• 2nd law of Thermodynamics: $CSB = GPP – CRs$
• THEREFORE,
  • If $O<em>2 > CO</em>2$, Biomass accumulates (E is > 1)
  • If $O<em>2 = CO</em>2$, New biomass is just enough to replace dead biomass (E is = 1)

Virgin Forest – Gaps, Building and Mature Phases Succession Cycle

• Respiration increases with increasing age of ecosystem development. More $CO_2$ is interpreted as a means to pump out disorder (or Entropy) and maintain ecosystem integrity/stability while there is no more growth. Production is for maintenance.

Summary