L13 - Temporal patterns Flashcards
define what an ecological succession is
progressive change in community composition, separated into primary and secondary succession
define primary succession and give an example of where it could be seen “in real time”
start from the beginning, “bare rock” eg volcanic island forming, an example is Krakatoa island, sruveyed across the years to see the process of the newly formed habitat being colonized
define secondary succession
a disturbance within an ecosystem, eg light gap, landslide, basically something that clears the way for species to colonize a newly formed free patch
in a temporate forest, what kind of plant is likely to come first (and what are the ones following)
annual plants usually first to come, then perennial and grasses, shrubs then softwood and hardwood trees
what are the stages of succession in a tropical forest
Stand initiation phase (0-10y)
Stem exclusion phase (10-25y)
Understory reinitiation phase (>25y)
what happens in a stand intitiation phase
Germination of seed/seedling bank and newly dispersed seeds
Resprouting of remnant trees
Colonisation of pioneer trees
High rates of seed predation
Establishment of shade-tolerant species
what happend in the stem exclusion phase
Canopy closure
Growth suppression of pioneer
and shade-intolerant species
High mortality of short-lived
species
Growth of shade-tolerant
species
what happens in understory reinitiation phase
Mortality of pioneer trees
Reproductive maturity of
shade-tolerant species
Formation of canopy gaps
how does biodiversity change through the process of succession
medium during stand phase, highest during stem exclusion, lowest during understory
how can reduction in biodiversity be a misleading thing to observe
may suggest that the forest progressed into maturity rather than it being a “bad” thing, less species can sometimes be a good indicator
what are the two approaches to explaining the process of succession (what colonizes and when)
determinism and stochasticity
explain what deterministic approach suggests about succesion
producers first, then consumers, succession functions on the basis of facilitation of earlier stages to later stages, community as a “superorganism”
explain what stochastic approach suggests about succession
communities are random, coexisting species are a result of similarities and adaptations
how is succession likely a combination of determinism and stochasticity
step by step (up the trophic level) is important, however first organisms to attive usually have high dispersal abilities and dispersal is stochastic, there is also a stochastic element to WHEN a species arrrives, if too early, the colonization will not be successful
how does Krakatoa and IBT help us understand the processes through which a new habitat is colonized
shows the balance of local extinction and immigration, suggests that immigration is stochastic, extinction/extirpation is deterministic, therefore changes in structure are deterministic but changes in species compostion likely stochastic
what are the three main approaches to reforestation
plantation, passive restoration and applied nucleation
what is plantation approach to reforestation and what are its pros and cons
replanting original species across the whole area, expensive, have more control over the composition, however will likely have fewer species than natural succession (more “man made”)
what is passive restoration and what are its pros and cons
taking cattle out and basically letting habitat regenerate itself, takes a long time
what is applied nucleation and what are its pros and cons
islands of trees, so a middle ground between the two other approaches, use of dispersal species to make the process quicker
what is high quality carbon in the context of carbon credits and reforestation
if reforestation is going to be the process for sequestering carbon from the atmosphere and therefore carbon will be available as a credit for others to buy, the carbon needs to be “locked” permanently and reforestation has to be long term and involve native species for a successful habitat to form - problem is the process is very slow and the market wants fast carbon
what role does stochasticity and determinism play in reforestation
there are some things (d) that can be accounted for like light, humidity, temperature, likely competitors and resource availability, however also some stochatic factors will likely come into play (success of dispersal, climatic events, spread of pathogens)
