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Ecology-of-Natural-Regeneration

What determines regeneration succcess?

  • Presence and scale of disturbance
  • Seed dormancy
  • Seed supply
  • Dispersal
  • Germination
  • Seedbed
  • Growth and survival of seedlings

Dormancy​

Length of seed viability varies by species

  • Acer macrophyllum: A few weeks
  • Pinus contorta: Up to 10 years on dead trees

What is seed dormancy?

  • Not all seeds germinate immediately - even under favorable environmental conditions

Dormancy of seed depends on:

  • Genetics/tree species
  • Environmental conditions

Why does it make sense for trees to produce dormant seeds?

  • Evolutionary adaptation to disturbance regimes

Types of dormancy?​

A: Endogenous or physiological dormancy

  1. Embryo dormancy: Most common type for trees in BC
  2. Immature embryo dormancy: E.g., Ash species
    • Embryo needs a period of warm/moist conditions for maturation
  3. Growth inhibitors in seed coat: Desert plants or those relying on animal digestion

B: Physical dormancy

  1. Impermeable to water
  2. Low permeability to gases
  3. Embryo growth restricted through mechanical resistance

Germination​

Conditions: 15-30 C; moisture; gas exchange; light

  1. Hydration: seed swells and seed coat breaks
  2. Physiological activation: Conversion of storage materials into sugars, nitrogen compounds, and lipids (fats, hormones, etc.); translocation to the mbryo to fuel growth; respiration increases
  3. Embryo growth and emergence: Cell enlargement and division; emergence of seedling

Seedling growth and survival​

  • Emerging seedling uses up food supply rapidly
    • Photosynthesis needed for food production
    • Development of foliage
  • Water supply is critical for succesful establishment
    • Root growth is then main priority

Natural regeneration triangle​

  • Seedbed
    • Microsite:
      • Shade
      • Organic layer
      • Vegetation
      • Herbivory
      • Pathogens
      • Erosion/Deposition
  • Environment
    • Solar radiation
      • Light intensity
      • Light quality
      • Heat
    • Moisture
      • Snow
      • Flooding
      • Drought
    • Frost
      • Heaving
      • Soil detachment
      • Damage to seedling
    • Site
      • Aspect
      • elevation
      • slope
  • Seed supply
    • Seed trees
    • Species
    • Quantity
    • Dispersal
    • Quality/Viability
    • Seed predation

Seed Supply​

Seed dispersal mechanisms

  • Airborne, floating on water: small seeds with tufts
  • Airborne with large or small wings
  • Animal transport without wings: Berry like seeds
  • Animal transport: cached or buried

Vegetation regeneration:

  • Coppice systems

Why do seed dispersal distances differ among species?​

Seed bed​

Most important function at establishment: Providing moisture

  • Too little water: Droguth
    • Damage through failure of the hydraulic system
    • Tolerance is highly species dependent
    • Tolerance related to stomata regulation
    • Starvation
  • Too much water - waterlogging
    • Damage through oxygen deprivation
    • Tolerance highly species dependent

Shade:

  • Partial shade preferred for germination
  • Important in warm-dry BEC subzones
  • Reduces moisture loss
  • Lowers day-time temperatures
  • Cover reduces frost-damage
  • However: can reduce growth after establishment

Light depends on:

  • Latitude
  • Aspect
  • Slope

Heat:

  • Most proteins denature at 55C
  • Seedlings are most affected due to proximity to the ground

Survival​

Seed:Seedling ratio

  • Defined as the number of seeds required to produce a successfully established seedling
  • Helps to identify the limiting side of the regeneration triangle

Regeneration in gaps:

  • Distribution across an opening depends on species, seed supply, seedbed and environment
  • Different species can dominate in different locations relative to the distance from the edge

Key Messages​

  • Overcoming dormancy in seeds depends on the type of dormancy
  • Germination and initial establishment is a highly sensitive phase with high mortality
  • Seed supply, seedbed and the environment determine successful regeneration
  • Seed dispersal depends on the physical properties of the seed, as well as on tree height and wind speed
  • The seed:seedling ratio provides a method to identify limiting factors for regeneration success