NR 326 Lecture 6 Succession

PAI : Periodic Annual IncrementAverage increment per year over a 5 or 10 year period Xem nội dung đầy đủ tại: https://123doc.org/document/4463810-nr-326-lecture-7-growth-and-yield.htm

Forest succession process

EvolutionDegradation

Grass Pioneer tree

species (very intolerant

Seral tree species

(increasing in tolerance

as replacement continues)

Climax tree species

(very tolerant)

3 Succession

Changing in forest structure

4 Succession

Changing in species composition

Changing in forest ecology

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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

Primary Succession

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.

8 Stand development stages

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

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• Site Preparation to favor a certain

• Light Tolerance

• Future species composition

• Regeneration mechanism advantage

• Density

12 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

 Thinning to shape desired future condition of the stand

 Species composition and stand structure/form

 Density/spacing arrangements

Stem exclusion stage Management implications

15 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

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Progression to this stage of stand development and length of

this stage can be adjusted through silvicultural actions

18 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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Accelerating succession by applied

intermediate disturbance

20 Impact of Succession on Forest Management

Heavy cuts selection Light

cuts

Light selection cuts

Great

disturbance to

the natural

Small disturbance to the natural

VS

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)

Early stages Later stages

The litter High percentage

of leaf tissue High percentage of woody tissue (branches,

twigs and stems)Decomposed

Nutrient

concentration Great nutrient concentration Poor nutrient concentration (nutrients

being locked up)Water

transportation Easy Difficult

The growth of forests decreases as they ageImpact of Succession on Forest Management

Sort cuttingcycle

VS

Impact of Succession on Forest Management

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Uneven-aged management (maintain a balance

of healthy, vigorous trees and a smaller number

of mature trees)

VS

Impact of Succession on Forest Management

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Fertilizing the forest to

prevent a nutrient limitation

(it is not cost-effective)

Today’s Goals

 What is ecological succession?

 Why is succession important to forest managers?

 How does succession influence forest management?

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Key Concepts

 Competition drives stand development

 Responses to competition are

 Individual tree and stand growth are

 As size increases, density decreases due to

limited carrying capacity

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How we often think of succession…

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Disturbance

Aspen is often invaded by

white pine—and then there are

three possible trajectories

2 Low-intensity surface fire maintains white pine

3 No fire allows maple and hemlock to replace white pine

1 High intensity fire and

return to aspen

 Multiple pathways

 One possible climax community?

 Disturbance at any stage

 Arrested succession

 Succession is influenced by disturbance:Biological legacies…

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Stand development

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