Lecture 3 - gap dynamics and regeneration

Question 1

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

Answer 1

Aubreville

Question 2

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

Answer 2

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

Question 3

what are natural parts of forest dynamics?

Answer 3

gaps - forests are not uniform

Question 4

how are gaps created?

Answer 4

• 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

Question 5

describe variation in gaps

Answer 5

• 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

Question 6

what is gap fraction?

Answer 6

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

Question 7

what is a definition of a forest?

Answer 7

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

Question 8

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

Answer 8

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

Question 9

what are the 4 different stages of succession within gaps?

Answer 9

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)

Question 10

what are pioneer and climax species?

Answer 10

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

Question 11

describe pioneer

Answer 11

early successional , secondary, light-demanders

Question 12

describe climax

Answer 12

late successional, primary, shade tolerant

Question 13

pioneer reproductive strategies

Answer 13

• 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

Question 14

describe pioneer seeds

Answer 14

• 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)

Question 15

describe pioneer leaves, wood and roots

Answer 15

• 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

Question 16

3 facts about pioneer species

Answer 16

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

Question 17

climax seeds

Answer 17

• 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

Question 18

climax species survival strategies

Answer 18

• 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

Question 19

climax leaves, wood and roots

Answer 19

• 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

Question 20

what is evidence suggesting disturbance and diversity are related

Answer 20

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

Question 21

what did the study on niche partitioning show?

Answer 21

that plants do partition along gradients of abiotic variables