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Density and Stocking

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Density 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 Density

1. Number of trees per acre2. Basal area per acre3. Stand Density Index4. Crown Competition Factor

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BA/ac = /

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Stand Density Index

• Based on the observed maximum size-density relationship, using1) 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 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 Index

10

100

1000

1 10 100

Dq

TPA

Slope ~ -3/2

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Stand 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

1.605q

10DNSDI

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Crown 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

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cwMCA

2i

i

a

MCACCF

i i

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Crown Competition FactorCCF < 100

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Crown Competition FactorCCF > 150

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Stocking

• 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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Stocking

1) Stocking Guides2) Stand Density Management Diagrams

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1. Stocking Guides

1. Species Specific2. 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 Guide

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Generic Stocking Guide

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White Pine Stocking Guide

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2. 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 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 size

0 10 20 30 40 50 60

Time (years)

Ave

rage

size

of t

rees

10x108x87x76x65x54x43x32x2

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Relationship between density and tree size

100 1000 10000Ln(Trees per acre)

Ln(A

vera

ge v

olum

e pe

r tre

e)

10x108x87x76x65x54x43x32x2

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Density (log scale)

Plant

size

(mea

n tre

e volu

me, l

og sc

ale)

Baseline measurement

1st re-measurement

2nd re-measurement

9th re-measurement

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Density (log scale)

Plant

size

(mea

n tre

e volu

me, l

og sc

ale)

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Density (log scale)

Plant

size

(mea

n tre

e volu

me, l

og sc

ale)

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Density (log scale)

Plant

size

(mea

n tre

e volu

me, l

og sc

ale)

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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