Stem Exclusion

Objectives

1. Understand the patterns and processes within the stem exclusion stage

2. Understand when processes of crown closure and self-thinning occur

3. Understand difference between stratification and differentiation

4. Understand relationship behind these biological processes and stand tending operations

Stem Exclusion

• Number of trees goes down

• Live crown ratio goes down

Crown Closure

• Early in dense stands

• Later in less dense stands

Self-thinning

• Does not occur at crown closure

• Still adequate growing space per tree for growth

• No available growing space

Stratification

• Separation into layers (strata)

• Separation is by species or cohort

Differentiation

• Separation within stratum by vigor

– Dominant

– Co-dominant

– Intermediate

– Suppressed

Differentiation

• Slightly older

• Better microsite

• Less competition

– Other vegetation

– Wider spacing

• Genetically superior

Stem

• Reflection of history

• Accumulation of growth

Tending

• Speeds up natural process

• Directs growth onto certain trees

• Reallocates growth within tree

• Increases total growing space

Self-thinning

• Growing space is limited

• Repartitioning of growing space

• Trees must get bigger to live

Fixed amount of growing space

• Large number of small things

• Small number of big things

• Small number of small things – space left over

Concept

Size

number

X

X

Concept

Size

number

Concept

Size

number

X

Concept

Size

number

X

Concept

Size

number

Concept

Ln

(size)

number Ln (number)

Relative density

• Number of trees / maximum number– Of that size

Concept

Size

numberX Y

RDI = x/y