Lecture 3 - gap dynamics and regeneration Flashcards

1
Q

who proposd a ‘gap mosaic’ model in the 1930s?

A

Aubreville

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2
Q

what are the 3 forest cycle main stages in the ‘gap mosaic’ model?

A

1) gap creation immediately following a tree fall or gap opening event
2) building or regeneration phase which is characterised by competition for light and other resources leading to regeneration and growth
3) mature phase where the high emergent forest canopy is re-established

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3
Q

what are natural parts of forest dynamics?

A

gaps - forests are not uniform

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4
Q

how are gaps created?

A
  • tress die and fall
  • trees may be blown down
  • struck by lightening
  • large branches break off trees
    when one tree falls it often brings down many more as crowns are meshed together by lianas
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5
Q

describe variation in gaps

A
  • vary in size- damage to vegetation below varies with gap size, composition of surrounding vegetation and type of forest
  • variation in light in different sized gaps - big changes to micro-environments
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6
Q

what is gap fraction?

A

defined as the fraction of sky visible through the canopy - quick way to estimate the percentage of open canopy above

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7
Q

what is a definition of a forest?

A

a canopy interspersed with a number of gaps of different sizes and in different stages of regeneration arranged in a mosaic

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8
Q

what is the most limiting factor in the understorey of rainforests and what effect do gaps have on this

A

light - gaps create diverse microclimates affecting light, moisture temp etc - gaps experience alot more sunlight compared to understorey

  • quality of light also changes with an increase in photosynthetically active radiation (PAR) - light that hits the floor is often more red light
  • understorey in often under percentage light plants require to photosynthesise
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9
Q

what are the 4 different stages of succession within gaps?

A

1) rapid colonisation by shrubs, lianas and seedlings of pioneer tree species
2) rapid growth of short lived light demanding species which form a canopy over 10-30 years
3) slower growing shade tolerant (climax tree) species grow in biomass and species richness below the pioneer canopy become taller
4) eventually the shorter lived species die and the more shade tolerant climax trees emerge and re-establish the tall canopy (75-150 yrs)

(however theres lots of variations in these patterns)

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10
Q

what are pioneer and climax species?

A

broad categorisation based in plant characteristics (functional traits) that influence growth survival and strategies in the tropical forest environment
- the pioneer- climax classification represent extremes on a continuum

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11
Q

describe pioneer

A

early successional , secondary, light-demanders

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12
Q

describe climax

A

late successional, primary, shade tolerant

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13
Q

pioneer reproductive strategies

A
  • produce lots of seeds
  • widely dispersed by wind and animals = species poort as good dispersal reduces development of distinct populations
  • short life span and turnover quickly
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14
Q

describe pioneer seeds

A
  • require light to germinate and are gap dependent
  • can lay dormant in soil seed bank until a gap opens producing favourable conditions
  • establish and grow quickly whilst light, nutrients and water are available
  • high rates of photosynthesis, respiration and transpiration( water use efficiency is low)
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15
Q

describe pioneer leaves, wood and roots

A
  • crowns are visually open branches to capture light maximally
  • leaves are large
  • wood density is low
  • roots are highly branched for effective acquisition of nutrients - can be mycorrhizal
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16
Q

3 facts about pioneer species

A

1) dont invest greatly in defence against pathogens and herbivores - trade off for growth
2) typically live for 10-30 yrs
3) most pioneer species belong to a few genera and families

17
Q

climax seeds

A
  • large
  • produced annually or less frequently
  • no dormancy
  • short range dispersal
  • seed banks contain few species
  • seedlings can maintain for many years without much growth - waiting for gap to open
18
Q

climax species survival strategies

A
  • low rates of respiration and photosynthesis compared to pioneer species
  • low rates of transpiration so they a high water use efficiency
  • great variation/continuum amongst climax species ability to utilise light when a gap opens and consequently growth rates vary
  • adapted to survival at the expense of rapid growth
19
Q

climax leaves, wood and roots

A
  • more branches than pioneer
  • leaves are small long lived- slower turnover rate
  • leaves are tough - contain chemical defences
  • wood density is high
  • roots are micorrhizal
20
Q

what is evidence suggesting disturbance and diversity are related

A
  • gap dynamics provide evidence that disturbance promotes diversity
  • species adapted to exploit different stages of succession
  • generates diversity in species number and ecological strategies
21
Q

what did the study on niche partitioning show?

A

that plants do partition along gradients of abiotic variables