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STAND DEVELOPMENT AND RELATIVE DENSITYSTAND DEVELOPMENT AND RELATIVE DENSITY

Ralph D. NylandDepartment of Forest and Natural Resources Management

SUNY College of Environmental Scienceand Forestry

Syracuse, NY 13210

Nyland - 2010All rights reserved

Use of all or parts of this permission prohibitedwithout express consent of Ralph D. Nyland

Background reading:

Chapter 17, in Nyland, R.D. 2002. Silviculture: Concepts and Applications.Waveland Press. Long Grove, IL. 2ed.

Sources cited:

Assman, E. 1970. The Principles of Forest Yield Studies. Transl. by. S.H. Gardiner. Pergamon Press Ltd. Oxford.

Baker, F.S. 1950. Principles of Silviculture. McGraw-Hill.

Berglund, J.V. 1975. Silvics. SUNY Coll. Environ. Sci., and For. Syracuse, NY

Dale, M.E. 1968. Growth response from thinning young even-aged white oak stands. US For. Serv. Res. Rpt. NE-112

Hall, O.F. 1955. Where does thinning fit into management of Lake States pulpwood stands. Proceedings of the Society of American Foresters Meeting. Oct. 24-27, 1954. Milwaukee., Wis. Soc. Am. For., Wash., DC.

Lareau, J. 1985. Growth Among Second-growth Northern Hardwoods at Two Locations in New York State Following Thinnings to Various Levels of Residual Relative Density. M.Sc. thesis. SUNY Coll. Environ. Sci. and For., Syracuse, NY.

Mar:Moller, C. 1954. The influence of thinning on volume increment. 1. Results of investigations. Pp. 5-32, in Thinning Problems and Practices in Denmark. SUNY Coll. For. at Syracuse, World For. Ser. Bull. No. 1, Tech. Publ. No. 76.

Nyland, R.D., C.C. Larson, and H.L. Shirley. 1983. Forestry and Its Career Opportunities. McGraw-Hill Book Co., NY. 4ed.

Roach, B.A. and S.F. Gingrich. 1968. Even-aged silviculture for upland central hardwoods. US Dept. Agric., Agric Handbk. No.355.

Smith, D.M. 1986. The Practice of Silviculture. John Wiley & Sons, Inc. NY. 8ed.Steneker, G.A., and J.M. Jarvis. 1966. Thinning in trembling aspen stands in Manitoba and Saskatchewan. Can. Dept. For. Publ. No. 1140.

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Thinning – done in stands PAST sapling stage

Tending

even-aged^

After Nyland et al. 1983

Sepa

rate

d in

tim

e

The time for thinning ...

- during the aggradation phase- PAST sapling stage- likely after stands reach 100% relative density

3

Thinning normally done during this time …

The time for thinning ...

- during the aggradation phase- PAST sapling stage- likely after stands reach 100% relative density

... but with timing influenced by financial and other economic factors

So what stand and tree attributes influence our choices ?

4

First, reconsider this ...

… trees differentiate in heights and diameters

… tree numbers decrease due to mortality

... beginning early in the aggradation phase

5

... and the implications

And for a stand …

Heights differentiatedthrough time …

Berglund 1975

Height developmentof one tree ...

What patterns for height growth ...

6

Like this …

Differentiated …

Assman 1970

Note the genetic factor ...

7

Differentiation into crown classes ...

... the best

... the fastest growing

... the best promise

... good trees

... growing well

... good promise

... poor condition

... poorly growing

... poor promise

... wretched trees

... weakly growing

... woeful promise

Note how crown position relates to radial growth of individual trees ...

Assman 1970

Best crownposition

Vol

ume

incr

emen

t

8

Same thing for northern hardwoods ...

Lareau 1985 ... trees of upper canopy positions grow the best

… after thinning

And for a stand …

... creating a diameter distribution

And it shows up in the diameter distribution ...

Diameter growthof one tree ...

9

Like this one ...

BC & WA

HM & OTHERS

… or this

Nissen 2007

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And other structures ...

Probably shade intolerants

Shade-tolerant andmixed species stands

Two-strata stands

Smith 1986

Differentiation ...

... by height

... by diameter

After Nissen 2007

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In even-aged communities, structure tells us something special about ...

- crown position and potential for future growth byindividual trees

... the bigger the better

- that crown position may indicate a species stratificationacross the stand

... and something different about the future growthpotential of different kinds of individual trees

Giving us different kinds of even-aged stands ...

This one for standsof shade-intolerantspecies These for stands with

a major component ofshade-tolerant species

… or 2-aged

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But what about volume production per acre?

What about degree of site utilization?

Do we have sufficient trees to fully capture insolationand convert it to biomass at the fullest possible rate?

... to know if this is a fully producing stand

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How do we measure degree of site utilization ?

... stand structure and tree attributes

DO NOT tell the entire story

So we use measures of stand

RELATIVE DENSITYRELATIVE DENSITY

A critical concept ...… for even-aged stands

RELATIVE DENSITY ...

... absolute density (e.g., BA/ac) expressed as a %

of some reference level

Average maximum density = 100% Relative density

But how set the reference level ...

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Bas

al a

rea

per

acre

Consider the production function ...

PURPLE shows the timewhen an unmanagedstand FULLY occupiesthe site ...

... at 100% relativedensity

PURPLE shows the timewhen an unmanagedstand FULLY occupiesthe site ...

Yet the difficulty of determining STAND AGE STAND AGE complicates

use of the classic production function as an assessment tool

for any single stand ...

... but consider this

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High relative density leads to stem exclusion ...

... in a predictable mannerBaker 1950

BA/ac

Decrease innumber / acre

(Surrogate for time)

To produce a specialized production function …

We can use the change in #/acas a surrogate for change in age

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But flip this specialized production functioninto a new form like this ...

STANDDEVELOPMENT

TRAJECTORY

BA/ac

NO/AC(Time)

After Roach and Gingrich 1968

#/ac

BA/ac

Expected development of unthinned oak stands …

A (100% relativedensity)

110

100

90

80

70300 500 700 900 1000 1200 1500

By evaluating real stand data through regressionanalysis, Roach and Gingrich fitted a stocking guide …

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Some characteristic conditions in stands at 100% relative density ...

… mortality apparent (dead trees)

… intermediate and overtopped trees have low vigorand grow slowly

… trees have a long dead length along main stem

… most trees have a low live-crown ratio

… little sunlight reaches the ground

… advance regeneration sparse, or short-lived if present

… stands look dark and crowded

... as with this white pine at 100% relative density

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… or this

… as in this even-aged northern hardwood stand

With high degrees of crowding ...

... leading to high rates of mortality

MORTALIT

Y … you sacrifice this by not thinning

… when you use long rotations forsawtimber in unthinned stands

NET PRODUCTION ...

…what you see on the ground

Physiologicalmaturity

... in unmanaged standsAfter Hall 1955

GROSS P

RODUCTION

And due to mortality …

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With high degrees of crowding ...

... leading to high rates of mortality

… and reduced radial increment

… like this

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Due to the effects of crowding ...

ReleasedCrowded

... bigger crowns... better growth

... same height

… but thinning lets us change the situation

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By thinning we manage the lossesand harness the growth ...

… by cutting excess trees

... reducing stands to a stockingthat controls mortality andstimulates growth

A new kind of production function

And we do it through planning with the aid of a stocking chart ...

... to determine the best relative densityand how to control it

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After Roach and Gingrich 1967

100% RD

B-level RD

Like this one for oaks …

STANDDEVELOPMENT

TRAJECTORY

BA/ac

NO/AC(Time)

Taking this general form …

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… and a new productionfunction for thinnedstands like this

… like this one for oaks

... controlling mortality andstimulating growth

Thinned back to B-levelrelative density ...

The production function in its usual form for thinned stands…

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… like this one for oaks

With B-level relative density …

… the target residual density for a thinned stand

B-level RD

After Roach and Gingrich 1967

% of maximum possible basal area

100% of potentialgross growth

% o

f max

imum

cur

rent

gro

ss g

row

th

After Mar:Möller 1954

Full gross growth at 60% of maximum stocking

Mar:Möller assessed annual volume growth for standscut to different levels of residual stocking …

What is B-level relative density ?

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% of maximum possible basal area

Annual production differed little from identical stands at aresidual stocking between 60% and 100% of maximum …

100% of potentialgross growth

% o

f max

imum

cur

rent

gro

ss g

row

th

After Mar:Möller 1954

Full gross growth at 60% of maximum stocking

Gross growth maximized in stands with a minimum of

60% of the maximum possible stocking ...

… suggesting that the stand fully occupied the site

… fully captured incoming solar energy and fixed

it to biomass at the fullest possible level

But how to use that informationto regulate thinning intensityand the time to thin again ?

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Mortality

HIGH levels ofmortality in standswith >80% RDAfter Mar:Moller 1954

We base it on this …

Optimalstocking

So we use this as a rationale for management …

After Mar:Moller 1954

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Keep stands in the GREEN zone …

~

... keeping stands between60% and 80% RD

A plan for rational management ...

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Production maximized by thinning to about

60% of the maximum possible level of stocking ...

... varying to some degree by community type

Some real examples ...

Steneker and Jarvis 1966

Dale 1968

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Optimalstocking

... keeping stands between60% and 80% RD

After Nissen 2010

Amazing …

… I can almost see the A line