L4 Gap dynamics

Question 1

Who proposed the gap dynamics model?

Answer 1

Aubreville in 1930s

Question 2

What are the three stages of the gap mosaic model?

Answer 2

1 - Gap creation immediately following tree fall
2- Building or regeneration phase, characterised by competition for light and resources
3- Mature phase, where the high emergent canopy is reestablished

Question 3

How are gaps created?

Answer 3

Trees die and fall 
Trees blown down 
Struck by lightning 
One tree fall may bring down multiple 
Large branches fall

Question 4

How do gaps vary?

Answer 4

In size, in the amount of damage created in gap creation and the type of forest

Question 5

What is the gap fraction?

Answer 5

The fraction of sky visible through the canopy

Question 6

What are the factors involved in creating a microclimate in the gap?

Answer 6

Amount of light
Wind blows more through gap
Moisture - air vapour pressure
Temperature

Question 7

What is the most limiting factor in the understory?

Answer 7

Light

Question 8

How much sunlight reaches the understory?

Answer 8

0.4 - 2% full sunlight/300m2

Question 9

How much sunlight reaches the forest floor in a gap?

Answer 9

8.6 - 24% Full sunlight/300m2. -tenfold increase

Question 10

What is PAR?

Answer 10

Photosynthetically active radiation

Question 11

What are the different stages of succession in ta gap?

Answer 11

Radio colonisation by pioneer species
Rapid growth of the short lived pioneer species, forms a canopy over 10-30 years
Slower growing climax trees increase in biomass and become taller below pioneer canopy
Pioneer canopy eventually dies, and climax species become emergent canopy

Question 12

What does pioneer and climax species refer to?

Answer 12

Categorisation based son plant characteristics that influence growth and survival strategies in the tropical forest environment, classification represents extremes on a continuum

Question 13

What are the pioneer species?

Answer 13

Early, successional, light dependent, secondary

Question 14

What are the general characteristics of the pioneer species?

Answer 14

Produce a lot of seeds that are widely dispersed
Seeds require light to germinate so are gap dependent, lay dormant in the seed bank until conditions are right
High photosynthesis and respiration rates.
Transpire rapidly
Crowns open to capture light, leaves big
Shorter lifespan, trade off: invest more in growth than in defence
Low wood density and highly branched
May be mycorrhizal
Live for 10-30 years

Question 15

Describe the distribution of pioneer species

Answer 15

Widely dispersed so are species poor and development of distinct populations is reduced

Question 16

What are some examples of pioneer species?

Answer 16

Cercropia, Musanga, Trena, Macaranga

Question 17

Where are the neotropics?

Answer 17

Tropical terrestrial ecoregions of the Americas and the entire South American temperate zone

Question 18

Where are the pantropics?

Answer 18

All tropics. distribution is one which covers tropical regions of both hemispheres

Question 19

Where are the paleotropics?

Answer 19

Tropical areas of Africa, Asia and Oceania

Question 20

What are the climax species?

Answer 20

Late successional, primary, shade tolerant

Question 21

What are the characteristics of the climax species?

Answer 21

Seeds often large, produced less frequently
Often recalcitrant, no dormancy period, may germinate on tree
Poor representation in seed bank
Seedlings can be maintained for years with minimal growth
low rate of photosynthesis and respiration
More branches than pioneer, leaves smaller and have a slow turnover
Often lots of chemical defences, tradeoff: survival instead of growth
Long lifespan
Wood density high
Mycorrhizal
Emerge after pioneer species, 70-150 years

Question 22

Why may gaps help explain the is the theory that disturbance and diversity are related?

Answer 22

Looks at how much niche partitioning contributes to how diverse the trees that reestablish in a gap are. Fits with gap dynamic, because different species may be adapted to different stages of succession, from gap opening to closure which generates diversity in species number and ecological strategies

Question 23

How does niche partitioning occur across a gap?

Answer 23

when species differentiate along gradients within gaps or among gaps of different size

Question 24

What are the three premises underlying the light partitioning hypothesis?

Answer 24

1) there is a gradient in light availability at the forest floor
2) tree species show a differential distribution with respect to light, and
3) there is a trade-off in species performance that explains their different positions along the light gradient

Question 25

Describe the experiment carried out by Poorter and Artis to investigate the light partitioning hypothesis

Answer 25

In a bolivian tropical moist forest, looked at light environment, growth and survival of saplings of 10 non pioneer saplings.

Question 26

What is the light partitioning hypothesis?

Answer 26

Differential growth of species in different light conditions, thought to contribute to coexistence of competitive rainforest trees

Question 27

What did the Bolivian forest study find with regards to a gradient of light availability on the forest floor?

Answer 27

There was a gradient, ranging from 0.2 - 10.6%

Question 28

What is the Crown Illumination index (CII)?

Answer 28

A visual estimate of the amount of light received by the tree crown

Question 29

In the Bolivian forest study, did trees show a differential distribution with respect to light?

Answer 29

Species occurred in similar environments but differed in their CII

Question 30

What weer the two studies looked at to determine whether gaps help explain high tree species diversity?

Answer 30

Poorter and Artis, In Bolivia, looking at premisses for the light partitioning hypothesis Hubbel, in Barro Colorado island, looking at light disturbances, recruitment and tree diversity

Question 31

How was the study on Barro Colorado Island conducted?

Answer 31

Looked at 1200 gaps of varying sizes over 13 years, study focused on a 50h plot of old forest growth, . Plants with a DBH >1 were tagged, measured, mapped and identified to species level

Question 32

What did Hubbell conclude about the study on Barro Colorado Island find?

Answer 32

recruitment limitation was the main factor determining local species richness and species composition in the BCI forest

Question 33

What factors and processes determine the species composition of regenerating gaps?

Answer 33

``` Size of gap, topography and microclimate Degree of damage caused in gap creation Composition of soil seed bank and seedlings present Re-sprouting of existing vegetation Natural seed dispersal into gaps Recruitment limitation Ecophysical response of seedlings Janzen-Connell hypothesis ```

Question 34

What is recruitment?

Answer 34

When a juvenile joins a population