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Density and StockingDensity and Stocking

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Density and StockingDensity and Stocking

• Potential of the land to produce wood is determined mainly by its site quality.

• The actual production or growth of wood fiber achieved on a given site is determined by the number, distribution and species of trees on the site.

• Two measures of the number and distribution of trees on a given site are "density" and "stocking".

• Density is a measurable "fact".

• Stocking is a "relative" assessment.

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Measures of Stand DensityMeasures of Stand Density

1. Number of trees per acre

2. Basal area per acre

3. Stand Density Index

4. Crown Competition Factor

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5

6

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8

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BA/ac = /BA/ac = /

10

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Stand Density IndexStand Density Index

• Based on the observed maximum size-density relationship, using

1) number of trees per acre (TPA) and

2) mean quadratic tree diameter (Dq), a.k.a.

• diameter for tree of mean basal area

• Incorporates both number and basal area per acre measurements

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Stand Density IndexStand Density Index

0

100

200

300

400

500

600

700

800

900

0 10 20 30 40 50 60

Dq

TPA

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Stand Density IndexStand Density Index

10

100

1000

1 10 100

Dq

TPA

Slope ~ -3/2

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Stand Density IndexStand Density Index

• Equates observed Dq and TPA to an equivalent TPA for the indexed Dq=10 in.

10

100

1000

1 10 100Dq

TPA

70060050040030020010050

1.605

q

10

DNSDI

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Crown Competition FactorCrown Competition Factor

• Reflects the area available to the average tree relative to the maximum area it uses if it were open-grown

i21i dbhcw

10043560

1

2

cwMCA

2

ii

a

MCACCF

i i

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Crown Competition FactorCrown Competition FactorCCF < 100

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Crown Competition FactorCrown Competition FactorCCF > 150

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StockingStocking

• Involves the comparison of a given stand to a "normal", or fully-stocked stand.

– Problem: "Has anyone ever seen a normal stand?"

• Assumes that "natural" mortality is solely a result of over-stocking.

• Concept of stocking is very subjective in nature.

• Stocking guides are the main method for assessing stocking.

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StockingStocking

1) Stocking Guides

2) Stand Density Management Diagrams

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1. Stocking Guides1. Stocking Guides

1. Species Specific

2. Require that you know trees per acre and basal area per acre.

3. Usually have 2 or 3 lines that are important: the A-line, the B-line, and sometimes the C-line.

• Above the A-line: overstocked

• Between A-line & B-line: fully stocked

• Below the B-line: understocked

• C-line: lower limit of “understocking” to reach the B-line in 10 years on an average stand

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Generic Stocking GuideGeneric Stocking Guide

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Generic Stocking GuideGeneric Stocking Guide

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White Pine Stocking GuideWhite Pine Stocking Guide

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2. Stand Density Management Diagrams2. Stand Density Management Diagrams

What are they?• Graphic tools which illustrate how DIAMETER,

HEIGHT, DENSITY and VOLUME change over time for pure, even-aged stands

Why use them?• Lead to understanding of stand dynamics• To plan/evaluate initial spacing and thinning

regimes

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2. Stand Density Management Diagrams2. Stand Density Management Diagrams

Basic Concepts Involve:• Stand Dynamics• Self-thinning Theory• Langsaeter’s Curve

0.15 0.40 0.55 1.00

Relative Density

Mea

n A

nnua

l Inc

rem

ent

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Spacing effects on tree sizeSpacing effects on tree size

0 10 20 30 40 50 60

Time (years)

Ave

rage

siz

e of

tre

es

10x10

8x8

7x7

6x6

5x5

4x4

3x3

2x2

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Relationship between density and tree sizeRelationship between density and tree size

100 1000 10000Ln(Trees per acre)

Ln

(Av

erag

e v

olu

me

per

tre

e)

10x108x87x76x65x54x43x32x2

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Density (log scale)

Plan

t si

ze (

mea

n tr

ee v

olum

e, log

sca

le)

Baseline measurement

1st re-measurement

2nd re-measurement

9th re-measurement

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Density (log scale)

Plan

t si

ze (

mea

n tr

ee v

olum

e, log

sca

le)

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Density (log scale)

Plan

t si

ze (

mea

n tr

ee v

olum

e, log

sca

le)

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Density (log scale)

Plan

t si

ze (

mea

n tr

ee v

olum

e, log

sca

le)

Maximum size-density lineMortality initiation line

Stands under-stocked

Zone of OptimumDensity Management

Zone of ImminentCompetition Mortality

Crown closure lineStand trajectories

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