NR 326 Lecture 6 Succession

Succession



The gradual supplanting of one community of plants by another



Accompanied by changes in stand structure and species composition

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Forest succession process

Evolution
Degradation

Grass

Pioneer tree species

Seral tree species (increasing in tolerance

(very intolerant

as replacement continues)

Climax tree species (very tolerant)

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Succession

Changing in forest structure

3


Succession

Changing in species composition

4


Succession

Changing in forest ecology

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Primary Succession

where the conditions are originally unfavorable for plant growth, such as bare rock. Gradual erosion and deposition in the area
allows early (hardy) pioneer species to colonize and survive

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Secondary Succession

Occurs after existing vegetation is removed such as after a flood, fire or mechanical process (agricultural). The soil is already fertile or/and
the seed was already in the soil, so plants can easily become established.

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Stand development stages

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Stand initiation stage

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Stand initiation stage








Follows major disturbances (wind, fire, clear-cut)
Regeneration of open space from seed, sprouts & advance regeneration

Pioneer species occupy
One cohort or age class
High density
Stage ends when canopy becomes continuous and trees begin to compete with each other for light and
canopy space

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Stand initiation stage
Management implications

• Site Preparation to favor a certain
• Light Tolerance
• Future species composition
• Regeneration mechanism advantage
• Density

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Stem exclusion stage

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Stem exclusion stage

The intolerant trees continue rapid height growth

while the tolerant trees occupy their

respective niche.

Competition is intense and density-dependent self-thinning occurs
Canopy continues to have one cohort. Both intolerant and tolerant trees may share the main canopy
Characterized by growth, competition and mortality produced spatial adjustments
Diameter Distribution change

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Stem exclusion stage
Management implications

 Thinning to shape desired future condition of the stand
 Species composition and stand structure/form
 Density/spacing arrangements

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Understory re-initation stage

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Understory re-initation stage



Big trees with larger crowns , so when one tree dies the surrounding trees can not fill the gap



Seed is produced, seedlings occur in the gap



New cohorts can eventually enter the canopy, diameter distribution becomes bimodal (2 peaks)



The stand reach their economic maturity

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Understory re-initation stage
Management implications

Progression to this stage of stand development and length of this stage can be adjusted through
silvicultural actions

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Old-Growth stage

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Old-Growth stage



Climax species dominate the site and reproduce successfully



Intolerant trees cannot reproduce



High structural diversity



Growth is slow or may be negative

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Impact of Succession on Forest Management

Accelerating succession by applied intermediate disturbance

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Impact of Succession on Forest Management

Heavy cuts

Light
Light selection
selection

VS

cuts
cuts

Great disturbance to the

Small disturbance to the

natural

natural

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Impact of Succession on Forest Management

If you are hoping to regenerate certain species naturally following a harvest, it is important to know what successional stage
these species typically occupy; and, what type of harvest will generate the desired conditions for stand establishment. (Jeff
Martin and Tom Gower, 1996)

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Impact of Succession on Forest Management

Early stages

Later stages

High percentage of leaf

High percentage of woody tissue

tissue

(branches, twigs and stems)

Decomposed process

Fast

Slow

Nutrient concentration

Great nutrient concentration

Poor nutrient concentration (nutrients

The litter

being locked up)

Water transportation

Easy

Difficult

The growth of forests decreases as they age

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Impact of Succession on Forest Management

Reduce the rotation length

Long
cutting
cycle

Sort
Sort cutting
cutting

VS

cycle
cycle

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Impact of Succession on Forest Management

Uneven-aged management (maintain a balance of healthy, vigorous trees and a
smaller number of mature trees)

VS

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