L4 Gap dynamics Flashcards
Who proposed the gap dynamics model?
Aubreville in 1930s
What are the three stages of the gap mosaic model?
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
How are gaps created?
Trees die and fall Trees blown down Struck by lightning One tree fall may bring down multiple Large branches fall
How do gaps vary?
In size, in the amount of damage created in gap creation and the type of forest
What is the gap fraction?
The fraction of sky visible through the canopy
What are the factors involved in creating a microclimate in the gap?
Amount of light
Wind blows more through gap
Moisture - air vapour pressure
Temperature
What is the most limiting factor in the understory?
Light
How much sunlight reaches the understory?
0.4 - 2% full sunlight/300m2
How much sunlight reaches the forest floor in a gap?
8.6 - 24% Full sunlight/300m2. -tenfold increase
What is PAR?
Photosynthetically active radiation
What are the different stages of succession in ta gap?
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
What does pioneer and climax species refer to?
Categorisation based son plant characteristics that influence growth and survival strategies in the tropical forest environment, classification represents extremes on a continuum
What are the pioneer species?
Early, successional, light dependent, secondary
What are the general characteristics of the pioneer species?
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
Describe the distribution of pioneer species
Widely dispersed so are species poor and development of distinct populations is reduced
What are some examples of pioneer species?
Cercropia, Musanga, Trena, Macaranga
Where are the neotropics?
Tropical terrestrial ecoregions of the Americas and the entire South American temperate zone
Where are the pantropics?
All tropics. distribution is one which covers tropical regions of both hemispheres
Where are the paleotropics?
Tropical areas of Africa, Asia and Oceania
What are the climax species?
Late successional, primary, shade tolerant
What are the characteristics of the climax species?
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
Why may gaps help explain the is the theory that disturbance and diversity are related?
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
How does niche partitioning occur across a gap?
when species differentiate along gradients within gaps or among gaps of different size
What are the three premises underlying the light partitioning hypothesis?
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
Describe the experiment carried out by Poorter and Artis to investigate the light partitioning hypothesis
In a bolivian tropical moist forest, looked at light environment, growth and survival of saplings of 10 non pioneer saplings.
What is the light partitioning hypothesis?
Differential growth of species in different light conditions, thought to contribute to coexistence of competitive rainforest trees
What did the Bolivian forest study find with regards to a gradient of light availability on the forest floor?
There was a gradient, ranging from 0.2 - 10.6%
What is the Crown Illumination index (CII)?
A visual estimate of the amount of light received by the tree crown
In the Bolivian forest study, did trees show a differential distribution with respect to light?
Species occurred in similar environments but differed in their CII
What weer the two studies looked at to determine whether gaps help explain high tree species diversity?
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
How was the study on Barro Colorado Island conducted?
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
What did Hubbell conclude about the study on Barro Colorado Island find?
recruitment limitation was the main factor determining local species richness and species composition in the BCI forest
What factors and processes determine the species composition of regenerating gaps?
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
What is recruitment?
When a juvenile joins a population
