Disturbance and Succession

Question 1

Disturbance

Answer 1

rapid physical change in ecosystem strucutre or resource availability

variable in size intensity, duration and frequency

this leads to new patterns of community composition and structure (local to regional)

Question 2

Two categories of succession

Answer 2

Primary:
Establishment and development of an ecosystem on newly formed substrate or after a cataclysm that leaves little or no organic matter or organisms.

Secondary:
Process of ecosystem recovery on a severely disturbed site or one that was previously vegetated

Question 3

page 7

Answer 3

page 7

Question 4

Minor disturbances - treefall gaps

Answer 4

Usually < 10% of canopy area is in treefall gaps

Highly localized damage and mortality

Increased light levels

Causes of tree death include pathogens, wind, lightning, etc.

Species differ in their growth responses to gaps

See slides

Question 5

Major disturbances - cyclines, fire, volcanoes

Answer 5

See slides

Conclusions:
Samoan forests sustained high damage from Cyclone Olaf. Species- wise damage rates (resistance) varied immensely.

Similarly, post-cyclone vital rates varied widely, but with a few notable species (e.g. Carica papaya, Macaranga harveyana) most species abundances remained surprisingly stable and community structure returned within 10 years, indicating very high community resilience.

Post-cyclone regeneration appears to be largely associated with species adult abundances; this may indicate that under conditions of increased cyclone intensity (climate change), the ‘rich get richer’

Question 6

Swidden agriculture (Brandrodung) and forests

Answer 6

Structure returns within a few decades

In some cases, forest composition is altered for longer than forest structure

What are the implications of this?

What are the alternatives to swidden? Are they
needed?
– “sustainable agriculture” versus land conversion

Question 7

Generally look through slides

Answer 7

see slides Lecture 7