Succession'

Question 1

Define primary succession

Answer 1

Succession on a barren, uncolonized terrain. e.g. substrate uncovered by a retreating glacier or created by an erupted volcano.

Question 2

Define secondary succession

Answer 2

Succession on soils which have already been previously colonized and have lost their community. e.g. after a forest fire or flooding, ; i.e. recovery of disturbed sites, usually seed banks.

Question 3

Stages of succession

Answer 3

Bare rock –> lichens –> mosses/ferns –> grasses/flowering plants –>shrubs –> Deciduous woodlands.

1st seral stage –. Lichens
2nd “ –> mosses/ferns
3rd – grasses

1st stage - abiotic factors are limiting conditions or drivers. At 3rd stage biotic factors become imp. in driving succession

Question 4

Define a climax community

Answer 4

Plants are in equilibrium with environment. Steady state has been achieved. Climax comms. look different in diff. biomes

Question 5

Clemensian view of succession

Answer 5

Close interactions create interdependencies between plant species that lead to predictable plant communities with co-occurring species and sharp boundaries. i.e. all species in the plant community respond in the same way to environmental gradients

Question 6

Gleasonian view

Answer 6

Suggested that species respond to environmental factors, so species do not consistently co-occur. Individual species have a unique set of requirements.

Question 7

The Climax State

Monoclimax hypothesis

Answer 7

All communities in a region are developing towards one regional climax community (uses geological time scale)

Question 8

The Climax State

Polyclimax hypothesis

Answer 8

Several different climax communities can develop in a region controlled by soil moisture, soil nutrients, animal activity etc.

Question 9

The Climax State

Climax- pattern hypothesis

Answer 9

Recognizes a continuum of climax types that varies gradually along environmental gradients. The climax is a steady-state community, in balance with environmental gradients.

Question 10

Conceptual models of succession

Classical Theory of Succession (= Facilitation model)

Answer 10

Species replace one another. Early species facilitate arrival of later species (fits with Clement’s view)

Question 11

Conceptual models of succession

Inhibition model of succession

Answer 11

Not ordered because it depends on who arrives first. Each species suppresses or excludes newcomers.

Question 12

Conceptual models of succession

Tolerance model

Answer 12

Any species can start the succession. Species are replaced by species more tolerant of limiting resources. Early successional species have little or no effect on later successional species.

Question 13

Example of primary succession?

Answer 13

Erupted on 18th May 1984. Mount St. Helens Volcano, Washington D.C., USA.
* Blast devastated an arc extending 18km north of crater
* Pyroclastic flows north of crater
* Mudflows south, east and west crater
* Tephra (Ash) deposited over thousands of square km

• 1st species to arrive was Lupinus lepidus (Lupine)
• Grew on mudflows and pyroclastic surfaces but seeds were poorly dispersed (heavy)
• N2 fixer. Die after 4-5 years and add N into soil. Acted as ‘nurse’ plants for other species

Question 14

Why does understanding succession matter?

Answer 14

• Community changes can affect land and water management.
• Need to understand the drivers of succession if we want to preserve a particular community. e.g. to preserve grasslands, one needs to understand optimum grazing intensity.
• Community change has implications for conservation
• Can enable predictions for successional development of new sites.