Lecs 3-4 Disturbance and Ecological Succession

Question 1

What is primary succession?

Answer 1

A process which denudes an area of soil. This can be a landslide, a volcanic eruption, or glaciation.

Question 2

What is secondary succession?

Answer 2

Less extreme disturbances, like fire, a hurricane, drought.

Question 3

What are the five stages of a succession?

Answer 3

Stage 1: Annual grasses.
Stage 2: Perennial Grasses
Stage 3: Shrubs
Stage 4: Shade-Intolerant trees
Stage 5: Shade-tolerant trees.

This is all organized by light tolerance.

Question 4

What is climax vegetation?

Answer 4

Climax vegetation is the predominant vegetation in a biome. The self-perpetuating species that replaces itself.

Question 5

What is the difference between resistance and resilience?

Answer 5

“Resistance” is an area’s resistance to change.

“Resilience” is an area’s ability to recover from a disturbance.

Question 6

What is a niche?

Answer 6

The function a life form serves in an ecosystem.

Question 7

What is secondary succession like in a mid-latitude broadleaf deciduous forest?

Answer 7

Main causes here are windfall and tree cutting.
Birch grows first, because it’s easily dispersed and is shade intolerant.
Sugar Maple and Beech eventually grown in
Beech can grow from its roots, and sugar maple is shade tolerant.

Pin-cherry depends on a seedbank, which activates when there’s increased nitrogen around, such as when trees are felled.

Question 8

What is secondary succession like in equatorial rainforest?

Answer 8

Main causes here are slash and burn, windfall, and clearcutting.

Soils have very little organic matter, so most of it’s locked into the plants themselves.
A windfelled tree exposes mineral-rich soil at the crown, while it crushes things at the epicentre and there are peripheral zones.

Question 9

What is secondary succession like in boreal forest?

Answer 9

Main causes here are fire cycles.

Tree canopies disappear, increasing light availability on the ground, pushing the permafrost layer back.
Shade-intolerant speices, like aspen and birch make their apperance.
But black spruce have serotinous cones, which open when exposed to fire.

Question 10

What role does the black spruce tree play in succession?

Answer 10

The needles are high in lignin, so they slowly release nitrogen into the soil.
Black spruce also decrease light availability, encouraging growth of lichen and moss.