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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 ...
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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
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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 ...
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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