USDA FOREST SERVICE G ENERAL T ECHNICAL REPORT PNW- 58
1977
TINNING
N YI LD 0
G
I
..
CONCEPTS
AND SOME ESTIMATES·
OBTAINED
BY SIMULATiON
DONALD L. REUKEMA
DAVID BRUCE
PACIFIC NORTHWEST FOREST AND RANGE EXPERIMENT STAT ION
U.S. DEPARTMENT OF AGRICULTURE
FOREST
SERVICE
PORTLAND. OREGON
Effects of thinning on yield of Douglas-fir:
Concepts and some estimates obtained by simulation
Abstract
Observation and research on yi lds of managed Douglas-fir stands have
given us many bits of knowledge, but no unified picture.
We assembled these
fragmented bits of knowledge into a conceptual model of stand structure and
development, which provides a basis for extrapolating results of studies to
conditions which have not been directly observed.
A stand simulator (DFIT)
provides details on number and size of trees and distribution of yield over
time.
Details and operation of DFIT are described in a companion paper.
This paper discusses concepts of stand development and effects of thinning,
provides guidelines for thinning, and summarizes current expectations.
We describe structure,mortality,
and growth of natural stands,
these attributes as a basis for
projections.
not been thinned,
been an
it would have
and use
We assume that had the stand
"average"
natural stand;
also discuss effects of some variations around this average.
but we
The major
source of gain from commerical thinning is harvest of merchantable trees
otherwise lost to mortality.
The two major sources of gains from precom­
mercial thinning are
growth onto trees that will reach
merchantable size
growth.
( 1 ) concentration of
and ( 2 ) improved height
The latter increases with
progressively poorer site·quality.
We recommend that precommercial thinning be done when leave trees are
10 to
15
feet tall
and
10 to
of improved height growth,
15
years old.
facilitate
and minimize possible subsequent
This will maximize the advantage
selection
of high-quality leave-trees,
amage to trees,
there are still worthwhile opportunities,
If this stage has passed,
but gains will be
less,
Average
spacing of these leave trees depends on desired tree size at the first
commercial entry;
that are left,
the larger the required size at that time,
If first commercial entry will
8 inches in d.b,h.,
with a minimum merchantable
precommercial thinning should 'leave
d.b,h,
the fewer trees
when trees average
of about
inches,
6
about 400-well-spaced trees per acre.
J
The first commercial thinning
stands,
be made
(or harvest) in precommercially thinned
should be when average d.b,h. of trees reaches the intended size.
To maximize merchantable yield of stands not precommercially thinned,
first commercial thinning should be made
trees begin to die.
the
about the time merchantable size
Just as number of trees left after precommercial
thinning depends on desired tree size
at the next entry,
so does the number
of trees left after the last commercial thinning depend on desired tree size
at final harvest,
But rather than reducing the stand to this number of trees
at a single commercial
thinning,
subsequent thinnings.
Thinning interval,
lesser extent,
excess trees may be carried for
removal at
level of growing stock,
type of thinning may be balanced
and,
to
over a wide range of com­
a
binations which will give the desired end product,
Thinning shifts the trends of mean annual increment
measure of volume,
over time.
Thus,
relativ
depend on the age at which comparisons are made.
tion of m.a.i.,
at culmination,
greater.
greater,
(m.a.i.),
by any
differences among treatments
At ages prior to culmina­
relative gains from only commercial thinning are less than
whereas those from precommercial thinning are a little
After culmination, relative gains from commercial thinning are
whereas those from precommercial thinning are a little less.
The proportion of total usable production remaining for final hal'vest
varies with thinning regime,
but
will likely be close to 70 percent of the
total merchantable cubic volume produced;
the other
30 percent being removed
in thinnings.
The proportion of board-foot production left for final harvest
In stands receiving only commercial thinning,
will be a little greater.
this final harvest volume will likely be no more than about 85 percent of
the volume that would have been harvested from the stand if it had not been
thinned.
The average d . b . h . o f trees cut at the f i nal h arve s t in t h i nned s t an d s
wi l l l ikel y b e f rom about 5 t o 3 5 percen t l arger t h an t h a t o f aZZ merch an t ­
Cons i derin g
ab l e trees cut a t f i n a l h arvest o f comparab le unt h i nned s t an ds .
t h e s ame n umbep o f l argest t rees , however , t h o se cut at f inal h arves t o f
st ands wh i ch rec e i ved o n l y commer c i a l t h i n n i n g wi l l b e about t h e s ame s ize
as those in unth in ned s t a n d s ; in s t an ds t hat were a l s o p recommerc i a l l y
t h inned , t hey wi l l be about 1 0 t o 1 5 percent l arger .
I n creased growth o f
res i dual trees i s o f f set b y remov a l i n t h i n n i n gs o f s ome l arger-t han - averag e
t rees t h at wou l d o herw i s e be present at f in a l harves t .
Gains in vo l ume produ c t i o n from o n l y commerc ial t h i nn i n g incpease wi t h
i n c reas i n g s i t e qual i t y .
The a d di t io n a l gain from precommerc i a l t h i nn i n g ,
however , is greates t on s i t e I V a n d decpeases with i n cre a s i n g s i t e qual i t y .
Rel at i ve gains from commerc i al t h i n n i n g decrease when l e s s o f the t o t al
vo l ume i s mercha n t ab l e; t h u s , t he g a i n s are less in t erms o f bo ard - f oot
vo l ume t han as c ub i c vo l ume .
The t ren d for gains from precommerc i a l t h i n ­
n in g i s jus t t he reverse-- greater i n t erms o f b o ard - f o o t vo l ume t h an as
c ub i c vo l ume .
Rel a t i ve g a i n s on d i f ferent s i t e q u a l i t ies a l s o vary w i t h
t he measure o f v o l ume .
KEYWORDS : Th i n n i n g ( t ree ) , t h in n in g ( precommerc i al ) , precommer c i a l t h in n i n g ,
t h i n n i n g ( co mmerc i a l ) , commer c i a l t h i n n i n g , growth ( f orest ) ,
i n cremen t , y ie l d ( forest ) , vo l ume i n cremen t , i n crement ( vo l ume ) ,
growin g s t o c k ( - i n crement / y iel d , mort al i t y , s t an d devel opmen t ,
s t an d s t r u c t ure , s t an d s ( even - aged ) , Dougl as - f ir , Ps e udots uga
menziesii.
CONTENTS P age
INTRODUCTIOX .
1
NATURAL STAl-,TDS
Descript ion o f A verage S t an ds
St and Stru c t ure and Devel opment
10rt a l i t y . . . . . . . .
Var i at ion Aroun d Average
1
2
4
6
6
SOURCES OF GAIN . . . . .
Commercial Th i n n i n g Cap t ures Merchan t ab le Mo rt a l i t y
Commer c i a l Th i n n i n g Impro ves Growth o f Res i dual Trees
Commerc i al Th i n n i n g Reduces C ub i c V o lume Growt h Per Acre .
Pre commer c i a l Th i nn i n g Concent rat es Growth on Mer chan t ab l e Tree s . . . . . . . . . . . . .
Precommer c i al Thi n n i n g I mproves Hei gh t Growt h and S i te I n dex . .
7
7
8
8
THI
8
9
10 10 11 I NG GU I DEL I NE S .
Precommer c i al Thi n n i n g .
Commer c i a l Th i n n i n g Reg i me .
RESVLTS OF THINNING .
umber an d S i ze o f Trees .
Vol ume Yield . .
15
15
20
EXTRAPOLATION TO OTHER STAND COND I T I ONS .
Un i forml y Under s t o cked S t an ds
Over s t o cked S t an ds . . .
Non constant S i t e Index .
I rregular S t an ds .
29
29
31
31
31
L I TERATURE CITED
31 APPEND I X .
G l o s s ary . Vari ables and Rel at i o n s h i p s Examined . . . .
S amp le DF I T P r i n t out . .
33
33
34
35
.
.
.
Introduction
I nt ens ive management o f commer ­
c i a l f o r e s t acreage provides many
oppo rtun i t i es to increase the amount
of u s ab l e wood produce d .
To t ake
advan t age o f these opportun i t i e s , we
mus t e s t imate how s t ands wi l l deve lop
under var ious man a gement regimes . The
g r e a t e s t need i s f o r p r e d i c t ions
wh i c h app l y t o t h e next generat ion :
youn g s t ands t h at have not yet p a s s e d
t h e p r e comme r c i a l t h in n i ng s t age and
s t an d s t h at wi l l be c r e at e d wh en
exis t in g s t ands are h arve s t e d . The s e
a r e t he s t ands wi t h the gr e a t e s t
oppor t u n i t y f o r i n t ens ive management
and max imum product ion .
A s e condary
need i s t o help set man ageme n t r e g imes
for t h e r ema ining l i f e o f current
s t an ds wh i ch may be comme r c i a l l y
The concern here is t o p r o ­
thinned .
v i d e for e f f i c ient t r ans i t ion f rom
t he current forest t o t h e new forest .
Th e s e pract i ces wi l l , in some cases ,
be qui t e d i f f e rent f rom tho s e f o l l owed
in s ub s equent forest rnt a t ion s .
In
b o t h cases , cho i c e o f
anagement
r e g imes mus t invo lve both economi c
and s o c i a l cons i de r ation s .
To e s t ima t e managed s t an d yie l ds ,
we f i rst assemb l e d our f r agment e d
b i t s o f knowl edge i n t o a concept ual
mode l , with as sumpt ions regarding
s t ruc t ur e an d deve l opme n t o f natural
st ands and t he resu l t an t e f f e c t s of
t h in n i n g.
This provi ded a basis for
ext r apo l at i n g resul t s o f studies t o
con d i t ions not d i r e c t l y observe d .
Resul t s of s t u d i e s were balanced
against deve l opment o f natural st ands ,
and against one ano t h e r , to derive
r e l a t ionsh ips amon g var ious s t and
p ar amet e r s and t o i n s ure cons i s t ency .
The variables an d re lat ionships
examin e d are l is t e d in t h e appen d i x . ll
appendix f o r samp l e DF I T p r i n t ou t .
W i t h i n t h e l im i t a t ions o f our mode l ,
e s t imat e s o f me rchan t ab l e y i e l ds ove r
a r an g e o f s i t e qual i t y , merchan t ab i l ­
i t y l imi t s , a n d t hi n n in g r e gimes appear
c o n s i st e n t a n d provide good e s t imat e s
o f r e l a t ive g a i n s f rom t h in n in g .
To
t he e xt e nt t h at y i e l ds w i t hout t h i n ­
n i n g may d i f f er , so wi l l y i e l ds w i t h
th inning .
S i n c e no s t ands in t h e P ac i f i c
No r t hwest have b e e n t h i n n e d re gu­
l ar l y for 60 t o 80 years , t h e y i e l ds
e s t imat e d by t h e s imul a t o r are e xt r a p o ­
l at e d f a r b e y o n d t h e ava i l ab l e dat a
base .
The e x t r ap o l at i ons s e em r e a­
s o n ab l e t o t he aut hors a n d sev e r a l
u s e r s , b ut t h i s i s no demo n s t r at ion
of t h e i r val i d i t y .
Th e growth
r a t e s and o t h e r f actors a f f ect i n g
y i e l d wi l l n e e d revision wh en
r e s u l t s of a c urrent cooperat ive
s t udy of mana g e d Dougl as - f i r y i e l ds
are p ub l i s h e d . 1
Th e purp o s e o f t h i s p ap e r is t o
c l ar i f y concepts r e gar d i n g s t an d
We t r y t o
s t r u c t u r e and devel opmen t .
e xp l a in g a i n s f rom t hinn in g .
W e f ir s t
d e s cr ib e as sumed charact er i s t i cs o f
natural s t an ds , s o urces o f g a i n f rom
t h in n i n g , and e f f e c t s o f t h i n n i n g on
From t h e s e
t he s e s o ur c e s of gain .
w e provide g u i de l ines f o r t h i nn in g .
We t hen i l l u s t r a t e and d i s cu s s r e su l t s
o f t h i n n in g , a s e s t ima t ed b y DF I T .
We e s t imat e t r ee s ize an d vo l ume
y i e l ds f o r s e l e c t e d s i t es, me r c h an t a­
b i l it y s t an dards , and t h in n i n g r e g imes ;
we supp l ement t h e s e est imat es w i t h
b r i e f d i s cu s s i o n s o f e f f e c t s o f a l t e r ­
n a t e t h i n n i n g r e g imes .
Final l y , w e
d i s cuss ext r ap o l at in g t o o t h er s t an d
conditions .
The p aper b y Bruce
e t al . ( 1977) provides the i n f o rmat ion
n e e de d t o u s e the s imul a t o r .
L i t t l e o f t h e informat ion i n c l ud e d in
t h i s report has been pub l ished .
We then const r uc t e d a s imu l a t o r
o f man aged s t and y i e lds ( DF I T--Dougl as­
f ir I nt e r im Tab l e s ) wh i ch e s t ima t e s
exp e c t e d s t an d deve lopment and y i e l d ,
wit h i n spec i f ied l im i t a t ions about
s t a n d charac t e r i s t i cs and t r e atment
See
r e g im e s ( Bruce e t a l . 1977).
1/
Sciences
Supporting data on file a t Forestry
Laboratory,
Olympia,
Washington.
Natural Stands
To prov i d e a b as e f o r evaluat i n g
e f f e c t s o f t h inn i n g on s t an d dev e l o p ­
ment , w e des c r i b e t h e development o f
" average" n at ur a l s t ands .
A l l our
/
Some a s s umptions and resulting
estimates may require revision when a coop­
erative study of managed stand yields is
completed.
This study is being conducted
by Robert O. Curtis, Pacific Northwest
Forest and Range Experiment Station,
Portland, Oregon, and James Arney.
Weyerhaeuser
Company.
Centralia.
Washington.
project i ons o f s t and devel opment
ith
t hinn i n g ar e made with t h e a s s umption.
that , had the s t and not b e e n t h in ed ,
it wo uld h ave had these ave r a g e
n atur a l st and at tribut e s .
Some char ac­
t e r i s t i cs of aver age nat ura l s t ands
are summar ized in the f o l l o w i n g dis ­
cus s i on and i l lustrat io n s .
s l i gh t l y l ar g er on good s i t e s t han
As t r e e s b e come
on poor s i t e s .
l ar ger (older ) , t he trend i s
r ever s ed; f o r a g iven h e i gh t , D g
i s sma l l er o n good s i t e s t h an o n
poor s i t e s.
.
D E S C R IPTION O F A V E R A G E S TA N D S
The eff e ct s of s i t e and age on
( Dg ) / and on number o f t r e e s and
b as a l ar e a Der acre are s hown in
f i gur e l . i/ Dg incr e a s e s w i th age.
number o f t r e e s de cr e a s e s as Dg
i n creases, and t h e r e sul t in g basal
area p e r acre i n creases with age ;
t h e b et t er the s i t e qual i t y , t h e
mor rap id t he rat e o f chan g e .
he
re suZting r e l at ionship b e tween D g ,
numb e r , and b as al ar ea i s shown i n
f i gure 2 .
F o r l ack o f c l ear evidence
to the contrary , we assume t h i s r e ­
l at i onship : 0 b e independ ent of s ite
and age ; th i s de fines a s t and
Th e
den s i t y index (Reineke 1 9 3 3 ) .
s t and s t a r t s out with several t hou­
s and t r e e seedl i n gs per a c r e .
As
t h e t r e e s increas e in s iz e , t h e
sma l l e r t r e e s are crowded o u t o f
t h e st and b y t h e ir mor e v i gorous
n e i ghbors.
By the t ime the D g of
t r ee s reaches 24 inches ( 6 1 cm ) ,
o n l y about 100 t rees p e r acr
( 24 7
p e r ha ) r emain .
The major e f fect o f s i t e i ndex
is on the r te o f s t and deve l opment;
t h e b e t t er the s i t e , the e a r l i er
t h e age at wh i ch a given Dg i s
r e ached .
The r e l at i on s h i p b e t we e n
h e i ght o f domi n an t t r e e s a n d o t h er
st and at t r ibut es do es not appe a r to
be independent of Si t e , h owever , as
has o f t en b e en a ssumed (f i g . 3 ) .
Our expe r i en ce has shown t hat Dg-­
and thus vo lume per acr e - - at a g iven
dominant h e i gh t var ies w i t h s i t e
index .
Wh en t r ees ar e sma l l , D g
correspondi n g t o a given h e i gh t i s
I
A s used throughout this paper,
refers to average d.b.h.; i.e.,
a tree of mean basal area.
il
Dg
2
.§.
w
w
'r
"I
170
20
a;
...
18
a:
16
a;
14
w
...
Q
iii
"l
110
80
10
8
6
4
2
0
0
5000
140
10
20
SITE INDEX
B
30
40
50
60
70
So
90
30
40
50
60
70
80
90
100
8R;:e
N ___
4500
w
II
II
<Jl
...
a:
:;
4000
3500
3000
2500
2000
1500
1000
500
0
0
10
20
100
S
.
"
"
III
..J
140
110
2S0
!
U
"
a:
170
300
80
> f
200
150
100
<Jl
SO
0
0
10
20
30
40
50
70
60
AGE (ye.rs)
d.b.h. of
Derived by reanalysis of data on
which USDA Technical Bulletin 201 (McArdle
et al. 1961) was based, plus additional
data for young stands.
13
28
2B
24
80
90
100
Figure l.--Descriptors of natural stands by
age and site:
A,
Dg of all
number of trees per acre;
per acre.
C,
trees;
B,
basal area
...
NUMBER OF TREES PER ACRE
F' gure 2 . --R e1 ationship aroong Dg,
number of
and basal area per acre i n natural
trees,
stands.
170
20
40
slo'
, I,
so
, I ,
100
o
140
I
HEIGHT OF 00 MINANTS AND COOOMINANTS
Figure 3
_
.
-
U:e ;:)
SITE INDEX
100
I '
150
zoo
-Relationsh' p becween Dg and hei gnt
'
of dom nant and codominant trees i n natural
stands.
3
STAND STRUCTURE A N D D EVEL O P M ENT
We have bro ught D g , n umber o f
trees, and basal area t ogether in t o
a single graph , a s i n f i gure 2 , t o
f a c i l i tate examination and d i s cu s s i o n
o f how stands deve l op over t ime and
t he effect o f t h i n n i n g on that
developmen t .
We wi l l b uild upon
t hi s f i gure in s u b s equent ill u s t ra ­
t io n s .
In f i gure 2 t he number o f
t rees decreases f rom l e f t t o ri ght
so t hat t he t ime sequence of stan d
development pro gres s es in t he c o n ven ­
t io n al manner , from left t o ri ght .
The di agon a l l ines , connect i n g poin t s
o f equal Dg , show t he mat hema t i cal
rel at ionship amo n g t he t hree variables .
For any comb inat ion o f two of t hese
vari ables , t he correspond i n g third
vari ab l e can be read for t ha t p o i n t
on t he graph .
There is a wi de range in s ize o f
l i vi n g rees at an y t ime .
Thus , the
largest t hird of the trees i n a s t an d
in c l udes about 55 percent o f the b a s a l
area per acre and t he sma l le s t t hird
i n c ludes o n l y about 15 percen t of t he
t o t al basal area ( f i g . 4A ) .
The
l argest third is mo s t l y domi nant s
a n d co dominan t s t hat are growin g
wel l ; the sma l le s t third i s mo s t l y
s uppres sed trees that h ave nearly
Development o f t he
s t opped growing .
s t an d over t im e i s shown in f i gure 4 B ,
<OO
c
•
80 S·
70 ;:; •
0.
1J
:;
E
..J
0
...
i
:
I
I
I
I
I
I
I
I
I
so
60 ..J !D
A
INTERMEDIATES
"
:
SUPPRESSED
50 40 30 20 10 �������J-�J-J-J-J-�J-�
o
10
20
30
40
50
60
70
80
90
100 TOTAL NUMBER OF TREES
(cumulaced percent]
Figure 4.--Structure and development of
natural stands:
A,
Cumulated contribu tion
of successively smaller trees to number and
basal area per acre;
B , successive curves
of cumulated contribu tion at progressively
older ages.
400 300 ....,
j,)
Q)
Q)
"-
Q)
c..
ro
::J
IJ"
IJ)
'-'
W
IT
U
<:{
200 100 80 so
IT
W
D<:{
W
IT
<:{
..J
<:{
(f)
<1:
m
40
30
20 2.000
'.000
SOD
400
300
NUMBER
200
100
OF TREES
80
PER
so
ACRE
40
30
20 10
s hown b y a v e r t i c al l ine acro s s
t hi s s h e af o f cur v e s ( fig. 5A ) .
Thus , for examp l e , while Dg of t h e
t o t a l s t an d incre a s e s from 3 . 0 t o
7 . 0 inc h e s ( 7 . 6 t o 1 7 . 8 cm ) - -wit h
a lo s s of about 1 , 650 t r e e s p er
ac r e ( 4 , 080 p e r h a ) --Dg of t h e 400
lar g e s t t r e e s p e r a c r e ( 9 90 p e r ha )
incre a s e s from about 4 . 3 to 8 . 0
in c h e s ( 10 . 9 t o 20 . 3 cm ) .
where cu rves of t hi s cumulat ed con­
tribution of t r e e s at successively
old e r ages are plo t t e d relative to
t h e t o t a l numbe r of living t r ees .
The six curve s p l o t t e d are for ages
when the t o t al numb e rs of trees in
t h e s t an d are 3 , 200 , 1 , 600 , 800,
400 , ?OO, and 100 , r es p e ctively .
The 100-percent curve ( s t r aigh t line
on l o garit hmic s ca l e ) is the s ame
curve shown in figure 2; t his curve
is t raditionally c a l l ed ORMAL in
t h e Unit e d S t a t e s .
The port ion of
the s t an d wi thin each crown class
is the s ame as in figure A.
A s t h e s t an d grow s , t h e number
of t r e e s lar ger t h an a s p e cified
minimum d . b . h . inc r e a s e s fo r a time
as more t r e e s grow to t h a t size
( fig . 58 ) .
Eventually the smaller
of t h e s e t r e e s b e come su p p r e s s e d
and sub s e quent l y die .
Thus , t h e r e
Th e d e velopment of any numb er
of lar g e s t t r e e s in t h e stand is
w
U
q
J:
w
11
<!
w
[
q
ill
<:'
ID
:1
c
3C
2Cl
A
1,000 8CXJ
3=
2.=
III
:;
Figure 5.--Development of stand
relative to
cotal
of largest trees;
specified d. b. h.
stand:
B,
omponents
A, ."ixed number
trees lar er than
!!
:11
600
4=
600
4=
300
200
,=
200
6t/)
UJ
D
q
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ell
100
so
so
5:)
40
1,000 soo
NUMBER
OF
3CJCJ
TREES
2C)(J
PER
ACRE
,=
is a maximum number of tTees that
will reach any specified d.b.h. At
the point where this maximum is
reached, trees larger than this
d.b.h. comprise about 63 percent
of all trees in the stand and about
80 percent of the total basal area.
We call this 63-percent curve
MAXIMUM.
Its importance will become
more apparent in subsequent dis­
cussion. The portion of the cumu­
lated-stand curve which is above
MAXIML
represents suppressed trees.
MO RTALITY
An average natural stand loses
about 1.5 percent of its trees for
each 1 percent increase in Dg.
Dg of trees which die each year is
about two-thirds the Dg of the
stand.
We have divided this mor­
tality into two components--trees
smaller than the specified minimum
merchantable d.b.h. and trees
larger.
The latter comprise the
part of mortality that can be sal­
',,-aged or preven ted by commercial
thinning.
When the merchantable component
of a natural stand reaches· 1AXIMUM
(fig. 5B), many trees which are
still alive have not yet attained
the minimum merchantable size--and
most of these submerchantable trees
never will.
ost of these sub­
merchantable trees are suppressed
and will die sporadically over an
extended period.
On the average,
the rate at which they die is a
function of the rate of stand
growth; the number of live trees
smaller than any specified minimum
d.b.h. is a fUnction of Dg of all
trees in a natural stand (fig. 6).
On good sites, most submerchantable
trees will die before the time of
final harvest.
On poor sites,
many of them will still be alive
at final harvest.
Volume of these
small trees is similar on all sites;
as a proportion of total volume
produced during a rotation, such
submerchantable volume is relatively
minor on good sites but is substan­
tial on poor sites.
Once the maximum number of
trees larger than a specified d.b.h.
is reached, merchantable trees in
natural stands die at a rate which
complements the submerchantable
6
",7
.
3CO
20Cl
0
J
cr
!.
w
a:
u
<i
a:
w
Q.
<i
W
a:
<i
..J
<i
II)
<i
;n
100
90
60
50
40
1.0Cl0 900
Figure
600
6. --Remaining number of submerchantabl e
and merc.':a.ntabl e trees in na t:.Jral stands
when mini.:num merch.antable d.b.h.
is
6.0
inches.
mortality (fig. 6).
This merchant­
able mortality in natural stands is
related to declining tree vigor.
In thinned stands. most of these
trees should be cut before they die
or, at least, they should be salvaged
after they die. With more growing
space, tbe life and growth of some
trees may be extended.
VA RIA TIO N A R O UND A V E R A G E
I n reality, there i s wide varia­
tion around this average natural
stand.
On plots from which this
average was derived, number of trees
at a given Dg varied from about 65
to 150 percent of the average;
variation was similar for all sites
and for the range of Dg included.
Other plots have been observed where
number of trees with a given Dg have
exceeded this average by more than
50 percent, but such extreme density
is not common.
The reasons for the
variation around th€ average differ
from one stand to another, and each
has a different effect on stand
structure and development.
Eflects
of some of these differences in
s and structure will be alluded to
.in the section regarding extra ola­
tion to other stand conditions.
440
Sources of Gain
Thinnings provide wo s o u r c e s
o f g a i n in us able y ield :
t he harv e s t
o f mer chantable
r e e s whi ch have died
or s oon would d i e and t he imp r o v ement
o f gro w h ra e of t re e s t hat are l e f t .
We f i rst di scuss g a ins ( and lo s s e s )
a s s o cia t ed w i t h commercial hinning-­
which is commonly a p a r t of r e g imes
"
b e g inning wit h p r e commer c i al t hi nning . Q/
We t hen discuss ga ins as s o c i at ed
w i h precomme r c i al t hi nning--which
we consider dded g a ins r elat i v e t o
commercial hinning alone . M E R CHANTA B L E M O R TA LI T Y
The maj or source of gain f rom
comme r c i al t hinning i s har ve s t o f
me r chantable r e e s t ha t would
o t he rwi se be lo s t t o mo rt ali t y .
The larger t he s i z e to whi ch t r e e s
are grown , the g r e a t e r i s t h e los s
t o mort ali t y ( f i gs. 5 , 6 , and 7A ) .
Thus, loss o f mer chant able produc­
t ion without commer c i al t hinning- ­
and po ent i al gain f rom comme r c i al
t hinning- - i s much g r e a t e r on good
I f com­
s i t e s han on poor s i t e s .
mer c i al t hinning i s st art ed e arly
enough , virt ually all mer chant able
mo r t ali t y can b e c ap t ur ed .
When
thinning is dela y ed , part of t he
me r chantable mo rt al i t y occurr ing
prior t o thinning will b e lo s t ;
but p art can be s alvaged when t h e
s t and is thinned .
Likewise, when an unt h i nned
st and is harve s t ed , some r e c ent
merchantable mor t al i t y c an be s al­
vage d .
Thus, mer chant able y i eld
har v e s t ed from a nat u r al s t and i s
a l i t tle gre a t e r t h an net me r chant ­
able y ield , and t h e gain f ro m
thinning is a l i t t le le s s t han t h e
di f f erence b e t w e e n t o t al me r c h ant ­
able production in t he t hinned
st and and net me r chant able y i eld
in t he unt hinned .
/
If trees are spaced widely
360
320
280
240
200
MERCHANTABLE NET YIELD
IN UHTHINNED STANO,
"".5 6.0+ /fiches In d.b.h. 160
121J J
i
C O M M E R CIAL THINNING C A PTU R E S
A
400
§,
"
•
80
40
���-L���-L��LO ��-L�
0
2
6
a
to t2 14 16 18
440
B
400
360
320
280
240
200
MERCHANTABLE NET YIELD
flees 6.0+ IfiChas 1(1 d.G.h.
160
IN UNTHINNED STANO,
120
80
40
00
OF UNTHNI">.IED STAN:)
[JI"CI"oeaj
Figure 7.--Sources of gain from
thinning, relative to normal
stand Dg:
A,
Capture of
merchantable mortality with
commercial thinnings
B, concentration of growth
onto merchantable trees with
precommercial thinning.
enough,
precommercially thinned stands may be
carr ied to final harvest with no commer­
cial thinning.
7
C O M M E R C IA L THIN N IN G IM P R O V E S
LOO
GRO WTH O F R ESID UA L T R E E S
Comme r c i a l t h in n i n g al so
impro ves growth rat e s o f i n d i v i dual
The g a i n in s i z e
r e s idual t r e e s .
o f t h e s e t r e e s , howeve r , usua l l y
d o e s not l e a d t o a sub s t an t i a l
i n c r e a s e in s iz e o f t r e e s at t ime
of f inal h a r ve s t .
Thi s gain is
l ar g e l y o f f s et b y removal of many
l ar ge r - t h an - av e r age t r ee s in t h in ­
n in g s ( Reukema 1 9 72 , Reukema and
P i en aar 1 9 7 3 ) .
C O M M E R C IA L TH IN N IN G R E D U C ES
C U B I C V O LU M E G R O WTH P E R A C R E
Tot al cub i c vo l ume growth p e r
a c r e i s reduc ed b y mo s t t hi n n i n g s
b e cause t r ees do n o t comp l e t e l y
o c cupy t h e area a f t e r t h i n n i n g .
A c t ual t r e n d s o f growt h over t ime
wi l l vary w i t h t h e t h i n n i n g r e g ime;
gr eat e s t r educ t ion s , r e l a t i ve t o
p o t e nt i a l , wi l l b e imme d i at e l y a f t er
e ac h t h inn in g .
W i t h i n f a i r l y w i de
l im i t s , however, t h in n i n g r e g ime
appe a r s t o have l it t l e e f f e c t on
t h e average p e r c e n t age r e du c t ion
in growth over an extended p e r i o d
( Reukema 1 9 72 ) .
I f r e s i dual s t o ck ­
i n g i s carr i e d at a h i gh e r l e ve l ,
growth may b e r e du c e d a l i t t l e l e ss;
if at a lower l ev e l , growt h may be
r e du ce d even mo r e .
Th i s d e p e n ds ,
howe ve r , not o n l y on s t o c k i n g l e v e l
b u t a l s o on whioh trees ar e cut .
For l ack o f b e t t er i n f o rmat ion ,
we e x p r e s s this r edu ct ion in growth
as a fun c t ion of s t and age at t im e
o f f i r s t c omme r c i al t h i nn in g ; t h e
o l d e r t h e s t an d wh en t h inn i n gs a r e
b e gun , t h e gr eat e r t h e r e l at iv e
r e duction in g r o w t h ( f i g . 8 ) .
Th e
ab i l i t y o f t r e e s t o respond t o r e l e a s e
i s r e l at e d t o t h e i r v i go r wh i c h , i n
turn , i s l o o s e l y corr el at ed w i t h age .
At a given age , t r e e s on good s i t e s
have r e l a t i v e l y s h o r t e r crowns t han
t h o s e on poor s i t e s , but t h e t re e s
o n g o o d s i t e s a dd t o t he s i ze o f
t h e i r crown s more r ap i dl y .
8
88
86
a
a:
.J
z
UJ
fa
a.
84
82
8
ua
88
fz
UJ
u
a: 86
UJ
a.
84
82
80 w---L---L---L-�L-�--�--�--�
20
2S
30
3S
40
4S
50
55
80
65
AGE AT FlRST COMMERCIAL THINNING iyears)
Figure 8.--Rela tive reduction in growth
between first commercial thinning and
final harvest, b y age a t firs t commer­
cial thinning.
P R E C O M M E R C IAL THIN N IN G C O N C E N TR A T E S
G R O WTH O N M E R CHA N TA B LE TR E E S
Precomme r c i al t h i n n i n g i n c r e a s e s
growth b y e l im i n a t i n g exce s s compe t i ­
t i on a n d c o n c e n t r at i n g a l l growth o n
t re e s t h a t wi l l b e come m e r c h an t ab l e
( f i g . 7B ) .
I n a n at ur a l s t a n d , as
crop t r e e s i n c r ea s e i n s i ze t h e y
gradua l l y crowd out t h e i r weaker
n e i ghbor s .
Crop t r e e s do not com­
p e t e s t ron gl y w i t h one another unt i l
t h e i r Dg app r o aches MAX IMUM ( f i g . 5B ) ;
howeve r , a sub s t an t i a l p ar t o f t h e
t o t al s t an d p r o duct ion h a s b e e n on
t r e e s t h at n e v e r r e ac h merchan t ab l e
s i ze , resul t i n g i n r e du c e d growth
on t r e e s t h at do .
In a p r e c ommer ­
c i al l y t h i n n e d s t and , o n l y c r o p t r e e s
ar e l ef t .
The s e t r e e s do not comp e t e
st ro n g l y wi t h o n e ano t h er unt i l t h e i r
Dg appro ach e s MAX IMUM, Rnd t h e y
reach t h i s s i z e sooner be cause o f
t h e e l iminat ion o f addi t i o n a l com­
p e t i t ion ; the e ar l i e r the p r e commer­
c i a l t h in n in g , t h e gr8ater the gain .
.
If two comparable stands are
preco ercially thinned to different
spacings, trees grown at the wider
spacing will eventually reach a
For a while, trees in
larger size.
both stands will grow at about the
same rate; but as the trees increase
in size, competition retards growth
sooner in the stand with more trees.
For example, by the time a stand with
400 trees per acre ( 9 9 0 per ha)
reaches the MAXIMUM stocking level,
trees in a stand with only 29 0 trees
per acre ( 715 per ha) will be somewhat
larger (fig. 9 ) .
--.----
.-
• .• -r ";".
-
...--
>
•••••• __ .,-
,
''
.....
... . .... ,. T"
'-"
-
.""""
.
• -
- '.
-,"--
!".'r-.,;,' '; " '•
trees per acre, the period to stand
closure is longer on poor sites than
on good sites; thus, relative
improvement in height growth is
greater on poor sites than on good
sites.
Likewise, the period to
stand closure depends on stand
density; the fewer the residual
z
Q
f-
1
a
1=
A
,10
....
« ,=
t!J
f-
ill
I
so
80
«
J
z
Z 70
<I.
.J
«
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a:
0 so
Z
2
sec
40C
300
"JUMBEq
Figure
2CC
::=
9.--Effect
100
TPEES
PER
SO
80
ACHe
of spacing of
attained d.b.h. and on basal
50
40
trees on
area per
ac=-e.
u.
0
....
Z
w
(.J
a:
w
il.
50
8
10
P R E C O MM E R CIAL THIN N I N G IMP R O V E S
12
14
16
18
20
AGE
22
24
{yeersl
26
28
3D
32
34
36
HE IGHT G R O WTH A N D SITE IN D E X
Precommercial thinning also
improves height growth.
Substantial
improvement is common on poor sites
(Reukema 1970 ) : apparent short-term
improvement has been observed on
better-than-average sites.
Spacing apparently has little
effect during the period when rate
of height growth is rapidly increas­
ing; however, in stands in which the
crown canopy has not yet closed,
this period of rapid height growth
is prolonged.
Thus, height growth
in open stands culminates at a later
age and at a higher rate than that
in the average natural stand
(fig. lOA).
'Iii th a given number of
HEIGHT OF OOMINANTS ANO COOOMINANTS
Figure lO.--Gains with precommercial
A,
[teet]
thinning:
Trends over time in height growth of
dominant and codominant trees;
B,
ment in site index.
9
.
".,-,--
improve­
timing o f th i n n i n g , average spac i n g
o f l eave tre e s , and s e l e ct i o n of
l eave tr ees.
To h e l p a manager
s e l e ct des i rab l e th i n n i n g r e gimes ,
we d i s c u s s each o f th e s e factor s .
We do not try to de f i n e a " b e st"
th i n n i n g r e g im e , nor do we d i s c u s s
al l factor s whi ch t h e manager should
c o n s ider i n determi n in g what i s b es t
f o r him .
trees , the longer th e p e r iod .
CUl ­
mination o f h e i gh t growth wi l l not
b e d e l a y ed inde f i n it e l y on open­
g rown tr e e s , so oth e r f actors must
be l imiting at wide spacings .
By the time th e stand c l o s e s ,
h e i ght growth w i l l h ave dec l ined
to th e n o rmal pepoentage rate and
w i l l f o l l ow the n ormal h e i ght growth
patt ern th ere afte r .
Th is has the
e f f e ct o f improv i n g s ite index up
to th e t ime o f stand closur e , and
th e r e a f t e r of maint a i n i n g it at the
h i gh e r l ev e l ( f i g . l OB ) .
Th i s
improvement i n s it e index i s n e gl i­
g i b l e on good s i t e s b ut very s ub­
stan i al on poor s i tes , wh e r e th e
stand may be r e l at i v e l y open f o r
many year s .
A f t e r stand c l o s ur e ,
the potent ial rate o f cub i c vo l um e
gr owth p e r acre appears t o b e about
th e normal rate f o r current s ite
index and age , r e gardl ess o f wh eth e r
or n o t a stand w a s p r e commercial l y
th inned ( f i g . 1 1 ) .
h us , the
inherent p roducti vi ty of the s ite
e x ce eds its capac ity to produce
under norma l l y den s e stand condi­
tions .
P R E C O M M E RCIAL THINNING
On l y a f ew h i gh l i ghts regar d i n g
p r e commerc ial t h i n n i n g w i l l b e s um ­
mar i zed h er e .
We suggest that readers
r e vi ew " Guide l in e s f o r p r e c omme r c i a l
th i n n i n g o f Douglas - f ir" ( Re uk ema
1 9 75 ) f o r mo r e detai l .
We r ecommend that p r e commer c ial
th i n n i n g b e do n e whe n l e ave tr e e s are
about 10 to 1 5 y ears o l d and 10 to l 5
f eet ( 3 to 5 m) tal l ( f i g . 1 2 ) .
Thi s
wi l l maximize the advantage o f imp r o ved
35
30-
30
28 t=2.8 ­
24 r::..
22
t-
25
20r
:. s
Poorest site
E-
t
.,
; 20
12 I­
:.0 C8­
st:
[
!:!:.
l­
X
88
!.OO
120
INITIAL SITE INDEX
140
:'80
(100-year-ba",)
200
Fi gure 11. --Relative improvement in si t e index and current gross cubic vol ume growth wi t h precommercial thinning. Thinning Guidelines
The e f f e cts o f th inning on
stand deve l opment depend on th e
p ar t i c u l ar th inn i n g r e g ime f o l l owed .
For both p r e commerc ial and comme r c i a l
th i n n in g , maj o r cons ide rations are:
10
UJ
X
10
______ _
5
20
25
TOTAL AGE (Years)
Fi gure l 2 . --Recommended time for precommercial
thinning, rela tive to height and age of
l eave trees.
h e i gh t g rowt h ( f i g . 10), f a c i l i t at e
s e l e c t ion o f h i gh - qu a l i t y l e av e t r ee s ,
and min i m i z e p o s s ib l e sub s e qu e n t
damage t o t r e e s .
I f t h i s i d e al s t a g e
h a s p as s e d , t he r e a r e s t i l l wor t hwh i l e
oppor tunit i e s f o r p r e commer c i a l t h i n ­
n in g ; but g a i n s wil l b e l e s s .
The average s p a c in g o f l eave
t re e s d e p e n ds on how l a r ge t h e t r e e s
are expe c t e d t o b e wh e n t h e f ir s t
commerc i a l t h inn i n g ( o r h a r v e s t ) i s
made; t h e l ar g e r t he t r e e s a t t h a t
t ime , t h e f ewer t h e t r e e s t h a t are
l e ft .
The numb e r of t re e s to b e
grown t o a s p e c i f i e d s iz e i n a p r e ­
comme r c i al l y t h i n n e d s t an d i s about
equal to the maximum numb e r t h at
reach t hat s iz e i n t h e a ve r a g e n at u r a l
s t an d ( f i g . 5B ) .
With the spacing
c o r r e s p o n d ing t o t h i s numb e r , a l l
t re e s a r e e xp e c t e d t o r e a c h m e r ch an t ­
ab l e s i ze .
When t h e d e s i re d t re e
s i ze i s r e a c h e d , mos t t re e s w i l l
s t i l l b e growi n g we l l a n d wi l l r e sp o n d
we l l t o r e l e as e .
Pro p e r s p a c i n g i s
m o s t c r i t i c a l on p o o r - qua l i t y s i t e s .
P r e c omm e r c i a l t h in n i n g at t h e
r e commen d e d t ime s h o u l d l e av e t r e e s
o f f a ir l y un i fo rm s i ze .
I f p r e com­
mer c i a l t h in n i n g is de l a y e d a p p r e ­
c i ab l y , it m a y b e n e ce s s a r y t o l e ave
a wider range o f s i z e s .
Larger
t r e e s c l o s e t o mer ch an t ab l e s i z e
shou l d g e n er a l l y b e r e t a in ed i n t h e
s t an d un t i l t h e f i rs t comm e r c i a l
t h i n n ing.
C O M M E R CIA L TH I N N I N G R E G IM E
Jus t as t h e num b e r o f t r e e s
l e f t a f t er p r e c omme r c i a l t h i n n i n g
d e p e n ds o n d e s i r e d t r e e s iz e a t
t h e next e nt r y , s o d o e s t h e number
of t r ee s a f t e r t h e Zast commer c i al
t h inn i n g d e pe n d on d e s i r ed t re e
s i z e a t f in a l h a r ve s t .
But r a t he r
t h an r e du c i n g t h e s t an d t o t h e
d e t ermin e d numbe r o f t r e e s a t a
s i n g l e commer c i al t h in n in g , e x c e s s
t r e e s may b e l e f t f o r r emov a l a t
sub s e quent t h in n i n g s .
Th i n n i n g
i n t e rval , l ev e l o f g r o w i n g s t o c k ,
and , t o a l e s s er e x t en t , t ype o f
t h inn ing may b e b a l an c e d o v e r a
w i d e range o f comb i n a t i o n s wh i c h
wi l l g i v e t h e d e s i r e d e n d p r oduct .
Cho i c e o f commer c i a l t h i n n i n g
r e gime , w i t h i n wi d e l im i t s , h a s
l i t t l e e f f e ct on t o t a l p rodu c t ion ;
i t d o e s a f f e ct t im i n g o f y i e l d and
t r ee s iz e d i s t r ib u t i on.
De s ir ed t im i n g o f t h i n n i n g s ,
r e s i du a l s t o c k i n g l ev e l , a n d t y p e
o f t h i n n i n g a r e so int e r r e l at ed
t hat d i s cus s in g o n e w i thout t h e
o t h e r s i s d i f f i cu l t .
S in c e t h e y
cannot a l l b e d i s cus s e d a t o n c e ,
we wi l l r e l at e e ach , i n d i v i dual l y ,
t o a s t o c k i n g gu i de ( f i g . 1 3 ) .
u
w
2300
•
L
J
IT
200
5
150
w
<!
[
W
n.
<! 100
W
[
<! 80
.J
<!
UJ
<!
60
OJ
800
400
300
NUMBER
200
OF
150
TREES
PER
100
80
60
ACRE
Fi gure l3 . --A thinning regim e maintaining
stocking level between RECOMMENDED RESIDUAL
and MAXIMUM / wi th maximum interval between
thinnings .
AXIMUM, as de f in e d p r e v ious l y , i s
t h e appro x im a t e maximum s t o ck i n g
l e v e l t o wh i ch a g i ven number o f
m e r c h an t ab l e t r e e s should b e grown
in a man a g e d s t a n d .
RECOMMENDED
RES I DUAL i s t h e m in imum s t o c k i n g
l e ve l t o wh i c h t he me r c h an t ab l e
p or t i on o f t h e s t an d wi l l b e r e du c e d
at e ach t h inn i n g ; f o r t h i s i l l us­
t r at i on , RECOMMENDED RES IDUAL is s e t
at a b a s a l a r e a l ev e l o f about 7 5
square f e e t p e r a c r e ( 17 m 2 / h a )
b e l ow MAXIMUM .
Tim in g of Thinn i n g
F i r s t Th inn i n g
T o maximize us ab l e cub i c vo lume
y i e l d , one shou l d make t h e f i r s t t h in­
n i n g at about t h e t ime m e r c h an t ab l e­
s i ze t r e e s b e g in to die .
There f o r e ,
11
f i r s t pos s ib l e t h i n n i n g is s e t at t h e
a g e when t h e mer chan t ab l e port ion o f
t h e s tand reaches MAXIMUM .
For st ands
r e c eiving only comm e r c ial t hinn ing ,
t h i s age is a fun c t i o n o f s i t e index
and s pe c i f i e d min imum me r chan t ab l e
d.b.h.
For s t an ds wh i ch have b e en
p r e comme r c i a l l y t h in n e d , t h i s age
i s also a func t i o n of age when the
s t and was pre comme r c ial l y t h inned
t o a spe c i f i ed numb e r of t r ees; t h e
ear l i er t hat s t o c k i n g dens i t y is
cont r o l l e d, the younger t h e age o f
t re e s a t f i r s t comm e r c ial t h in n in g
( f i g . 14 ) .
;::::::'-'
::0
40
30
::
o
80
A
!
!
90
The f ir s t t h in n i n g o f s t an ds
t h a t are only comme r c i al l y t h i n n e d
may b e de l ayed b e y o n d t h i s f ir s t
p os s ib l e age f o r t h i n n i n g .
Thi s
may b e e i ther a m i s s ed oppor t un i t y
or t h e r e s ul t o f a man a gement
ob j e c t ive other t han maximizin g
t o t al usab l e y i e l d .
I f t hi n n i n g
i s delaye d , mer chan t ab l e t r e e s wi l l
d i e out o f the s tan d at t h e natural
s t and rat e ( f i g . 5 ) .
Th e first com­
mercial t h innin g of prec ommercia Z Zy
t h inned s t ands shoul d not be de layed
app rec iab l y b e yon d the f ir s t p o s s ib l e
t h inn i n g age .
Th e s e s t an ds are mo r e
un i f orm t han natural s tands a n d are
not l ik e l y t o t h in t h emse l ve s e f f e c ­
t i ve l y; espec ia l l y ori poorer s i t e s .
I n s t ead , t hey may r e t a in an excess i ve
numb e r o f trees f o r a pro longed
period an d t e nd to s t a gnat e; e ventu­
a l l y , t h e r e l ik e l y w i l l be heavy
mor t al i t y ( f i g . 1 5 ) .
I
.
100
!
I
120
!
!
I
140
!
I
I
160
180
160
180
!
!
!
!
80
70
30
50
40
30
20
10
0
80
B
100
120
140
I
I
INITIAL SITE INDEX (10Dwyeal"'-baSls1
I
I
200
Figure l 4 . --Age at first possibl e commercial thinning, by ini tial si te index and mini­
mum merchantable d . b . h . (dm) .
A, when
dm is 6 . 0 inches i B I when dm is 7 . 5 inches.
Las t Th inn ing
300
Tim i n g o f t h e last t h i n n i n g
s houl d depend o n t h e d e s i r e d a g e
an d s t an d charact e r i st i c s a t f inal
harvest .
General l y , it wou l d appear
des irab l e to leave as much vo lume .
as prac t i cal for t h e f inal harvest-­
rat h e r t han remo v i n g mor e t r e e s than
n e c e s s ar y in th i n n i n g s .
A r easonab l e
ob j e c t ive wou ld b e t o have t h e s t an d
a t MAX IMUM s t oc k i n g l e v e l a t t ime
O n c e t h e s t an d
of f i nal harvest .
h a s b e en r e duced t o t h e n umbe r o f
t r e e s that are e xp e c t ed t o r e a c h
MAX I MUM l e v e l a t a des i r e d age ,
ano t h e r t h inn ing i s unn e ce s s ar y .
:;
2'
• 200
c
•
J
cr
.J!!. 150
w
II
U
"
II
w
a.
"
w
II
"
-'
"
!])
"
III
100
80
60
50
40
Th inn i n g I n t erval
I f s t o ck ing i s ma i n t a i n e d
b e tween o u r RECOMMENDED RES IDuAL
1.000 800
600 500 400
NUMBER
OF
300
TREES
200
PER
150
100
ACRE
Fi gure l5.--Effect of delaying commercial
thinning of precollvllerciall y thinned s tands .
12
I
200
__
,
.
.
_
1._..
•
\ •
.
,....
" _!Jo'.
a n d MAXIMUM levels (fi g . 1 3 ) , t h e
int erval between t h i nn i n g s
i s t h e t ime required t o grow about
7 5 s qu are feet per acre ( 17 m 2 per
h al i n b a s al area.
I f a s t an d is
t hinned more f requen t ly , it will
not b uild u p t o t h e MAXI MUM level ,
a n d each t h i n n i n g w i ll remove les s
volume .
I f t h i n n i n g s are. made less
f requen t ly , the g r ow i n g st ock level
at t a ined before t h e next t h i n n i n g
I f gr0w i n g
will exceed t h e MAX IMUM .
s t o ck i s allowed t o exceed t h i s
level b y ver y much , i n d i v i du al t ree
growt h may be severely ret a r ded .
l--Cornnel"aiaZ thinning ages oO'lTBsparuiing t<' suggested heigr.::­
g!'O'lJth 'intervaZ and adjusted fol' aompar;ibi Zir;y /Jith l'ota::-::.7.
aqeJ by treatment and mininn.on merchanr;able d.b.h.
Table
maxim u m
Th i s maximum i n t er val can be
clo sely app r o x imated b y f i xed h e i ght
g rowth i n t ervals , where the i n t er val
var ies b y s i te qual i t y - - f rom about
2 4 feet ( 7 . 3 m) on s i t e I to 15 feet
( 4 . 6 m ) on s i te V ( f i g . 1 6 ) .
The
c o r respon d i n g t ime i n t er v al between
t h i n n i n g s var ies sub s t an t i ally w i t h
s i te q u ality a n d s t an d a ge- - f rom
about 6 years in youn g s ite I s t an ds
to more t h an 30 years in s i t e V
s t an d s ( t able 1 ) .
Thi s i n t erval
c an be mo d i f i ed t o make it comp at ible
with desi red t im i n g o f the last t h in ­
n in g ; t h e r i ght -hand p o r t ion o f
t able 1 shows an example o f such a
mo d i f i c at ion .
With suggested
; nches
J
6.0
7.5
. inches
inches
Adjusted for compatibil ity
interval
+
PCTY
CTli alone
6.0
oH
25
32
40
51
65
(85)
30
38
48
61
(eo) 11
22
28
36
45
57
(74)
30
38
49
64
(86)
36
46
60
(80)
26
33
43
55
(72)
I
6.0
inches
inches
Site
l
CT alone
CT
7.5
I (85
PCT
7.5
6.0
J
incoes
'.5
; nches
inches
30
37
44
53
65
22
28
34
42
52
65
36
44
54
67
26
33
42
52
67
45
55
68
31
40
52
69
:
..
5':
6S
59
65
38
51
69
':;
5
5?
years)lI
25
32
40
51
65
24
31
38
48
62
(81)
+ C
2!
J:
JS
5D
:
Site II (90 years)lI
29
37
47
61
(82)
III (95
Site
36
47
63
(86)
45
60
(82)
31
40
52
(70)
47
65
(95)
59
(84 )
38
51
69
68
(110)
(89)
51
(74)
IV (100
43
58
(80) Site
V (105
59
(87) J5
--
2;
53
56
years)lI
35
46
60
(81) Site
Jj
y
1I
11
30
39
51
67
36
49
68
years)lI
47
66
years)lI
68
59
51
70
Conmereial thinning.
Preeo"",ereia 1 thinning.
Site class (rotation age).
Numbers in parentheses are ages at completion of next
thinning period.
.IH
Res i du a l Stock i n g Level
(Average Spacing)
Figure l 6.--Hei ght growth i n terval which will
maintain s tocking l e 7el approximatel y
between R ECOMMENDED RESIDUAL and MAXIMUM ,
by si te index.
At t h e RECOMMENDED RES IDUAL s t o ck i n g level , b as al area r an ges f rom b o ut 1 0 5 s q u are feet per acre ( 24 m per hal f o r la- i n ch ( 2 5 - cm ) t rees t o 2 2 5 square feet ( 5 1 m 2 ) f o r 3 0 - i n c h ( 76 cm ) t rees ; corres­
pon d i n g aver age s p a c i n g s of t rees are about 1 5 an d 3 1 feet ( 4 . 6 an d 9 . 4 m) .
We f u r t her recommen d t hat no more t han one- t h i r d of t h e mer ­ ch an t able basal a r e a b e r emo ved in a t h i nn i n g . I t would be reason able t o set
res i dual s t o c k i n g at ot her levels
for cer t ain s i t uat ions .
For example,
i f the t ime req u ired f o r trees to grow
fr om RECOMME DED R E S I DUAL to MAX I MUM
( f i g . 1 3 ) i s lon ger t h an the t h i n n i n g
13
i n t e rval d es ired f or a part icular
s t and , res i dual s t ocking could be s e t
at a h i gher level compat ib le wi th the
short er thi n n i n g i n t erval ( f i g . 1 7A ) .
On the o t her han d, s t ocking could b e
mai n t ain e d a t a lower average level
(f i g . 1 7B ) .
I n some ins t an c es , i t
would b e reasonab le t o t h i n a s t and
t o a s t o ck i n g l e v el b elow the RECOM­
MENDED l evel--w i t h a corresponding
redu ct ion i n grow h p e r acre .
300
"
.."
Type o f Thinning
(Selection of Leave Trees)
Type o f t h i n n i n g is d e f i n e d by
t h e diD rat io , whi ch is Dg of cut
t rees Cd ) relat i ve t o Dg of merchan t ­
able t rees b e f ore t h i n n i n g CD ) .
A
re aso n able trend o ver t ime can b e
e s t ablished b y relat i n g d iD rat i o
to Dg o f merch ant able t rees (D ) and
the minimum merchant able d . b . h . ( dm )
(f i g . 1 8 ) .
We sugges t that d i D at
t he f irs poss ible thinn ng should
be be tween 1 . 0 and 0 . 9 . §/ When dm
is 0 . 4 D or less, d iD should be about
0.8.
lCo
80
6-
w
[
U
60
[
w
0.
[
300
-1
In 200
Figure l 8 . --Regimes of diD ratio rela tive
to mimimum merchan table d . b.h . (dm) and
,
current Dg of merchan tabl e trees (D) .
ill
50
1 00
80
60
600
400
300
NUMBER
200
OF TREES
100
PER
80
60
ACRE
Fi gure l 7.--Maintaining residual stocking
l evel by frequen t thinnings: A, At hi gher
a verage l evel; B, at lower a verage l evel .
When thinning is done at the
" f i rs t poss ible " age , mos t merchan t ­
able t re es will b e capable o f respond­
ing t o releas e .
There fore , cut trees
c an b e proport ionately dis t ribut e d
across t h e ran ge i n merchan t able s i z e
If largest t rees are
( d iD
1 .0) .
not cut , d i D may drop t o about 0 . 9 .
On the other hand , the smaller mer­
chant able t rees could b e l e f t to grow ;
it is more import ant to pro perly
space des irable large t rees than t o
remove t h e s e smaller trees .
Leaving
thes e smaller t r e e s wo uld push d i D
back t oward 1 . 0 .
I n y o u n g s t ands ,
=
§./
It has not been uncommon for diD
to exceed 1.0 at first thinning on experi­
mental plots.
14
- ,.. .. .
t h e r e are opporcun i t i e s t o r emo ve
"o ugh dominant s ; t h e r e fo r e , diD on
goo d s i t e s ( younger ) cou l d be a
l i t t l e great e r t han on poor s it e s
( o l de r ) .
When f i r s t c h i n n i n g is d e l a y e d ,
me rchan t ab l e t r ees wi l l i n c lude
supp r e s s e d t r e e s , n o t capab l e of
r e sp o n d i n g t o r e l e as e .
A l so , n e i gh ­
b o r s o f l ar g e t r ees wi l l be l e s s ab l e
t o r e spond t o r e l e a s e .
Th e r e f o r e .
t he s i z e d i s t r ibut ion o f cut t r e e s
s ho u l d b e skewed t owar d t h e sma l l er
trees .
L ikewi s e , succe s s ive t h i n ­
n i n g s wi l l h a v e lower d i D rat i o s
b ec ause t h inn ing wi l l g e ne r a l l y
i n c l ude i n c r e as i n g p r o po r t ions o f
lower crown c l a s s e s .
The min imum
p o s s ib l e d i D rac io for a given p e r ­
c e n t c u c is dec erm i n e d by s t an d
s t ructure ; f o r examp l e . r emoval o f
o n e - t h i r d o f t h e b a s a l ar ea b y
cut t in g t h e smc : l e st t r e e s i n an
average natur al s t an d wou l d r e s u l t
i n a d i D rat io o f about 0 . 8 .
Results of Thinning
b . Terminat e s at an age compat ­
i b l e w i t h f in a l -har v e s t age ,
s o t ha t merchan t ab l e port ion
o f s t an d w i l l b e at app r o x i ­
m a t e l y MAX I MUM s t o c k i n g l ev e l
a t t ime o f f in a l harve s t .
c . I s done at t he l o n g e s t int e r ­
v a l s comp at ib l e w i t h o t h e r
e l emen t s o f t h e r e g ime ( t ab l e 1 ) .
d . R e du c e s me rchan t ab l e port ion
of the s t and , a f t e r e ac h
t h innin g , t o t h e RECOMMENDED
RES IDUAL s t o c k i n g l ev e l o r
t wo - t h i r d s o f i t s b as a l area
b e f o re t h in n in g , wh i chever
i s great e r .
e . Fol lows t he d i D r a t i o r e g ime
in f i gure 18 in wh i c h d i D
r a t io i s 1 . 0 at t h e f ir s t
t h i n n in g .
N U M B E R A N D S I ZE O F T RE E S
In the f o l low i n g d i s cus s ion o f
e f f e c t s o f t h i nn in g , a s est imat e d
by D F I T , o n n umb e r a n d s ize o f t re e s
harve s t e d an d o n vo l ume product ion ,
we emphas ize re sul t s app l ic ab l e t o
s e l e ot e d t h inn i n g re g im e s a n d g i ve
d e t a i l e d re sul c s p e r t inent c h e r e t o .
We i n c l u d e s upp l emen t ar y d i s cus s io n s
o f some e f f e ct s o f a l t e r n a t e r e g imes .
A l l r e sul t s obc a i n e d from DF I T app e ar
t o b e compat i b l e
i t h wh at we h av e
o b s e r v e d on exper imen t a l p l ot s .
Charact e r ist i cs o f t h e s e l e c t e d
r e g ime s are :
1 . Pre comme r c i a l t h in n ing , i f don e ,
i s done at age 1 0 , 1 1 , 1 2 , 1 3 ,
an d 15 y e ars on s i t e s I t h ro ugh
V) resp e c t ive l y .
2 . Minimum merchan t ab l e d . b . h .
6 . 0 i n c h e s ( 15 . 2 cm ) .
MAXIMUM s t o c k i n g l eve l
( fig . 1 3 ) .
is
3 . S t ands are c l e ar cut at age 85 ,
90 , 95 , 100 , and 1 05 ye ars o n
s it e s I t hrough V , r e s p e c t i ve l y .
4 . Commer c i al t h i nn in g :
a . I s b e gun a t t h e f i r s t p o s s ib l e
age ; i . e . , when merchan t ab l e
port ion o f s t an d r e ach e s
R e l at ion B et w e en Num ber and S i z e
Th e r e l at ion between numb e r
an d D g , t o ge t h e r w i t h how it i s
a f f e c t e d b y t h in n in g , is i l l u s t r a t e d
i n f i gu r e 1 9 .
Th is p art i c u l a r examp l e
i s f o r a s it e I s t an d .
The e xamp l e ,
however , app l i e s to a l l s i t e s ; o n l y
t h e a g e s a n d t h e number o f i n t e r va l s
wo u l d vary app r e c i ab ly . Th i s s t and
h as been t hi n n e d f i ve t ime s , b e g i n n i n g
a t age 25 , a n d carr i e d t o a ro t at io n
age o f 85 years .
Numb er a n d Dg o f
me r c h a n t a b l e t r ee s , at t ime o f e ach
t h i nn in g , are shown for both t h e
t h i n n e d a n d unt h in n e d s t ands .
Also
shown a r e t h e appr o x imat e cumu l a t e d
s t an d curves ( s ee f i g . 4 ) .
Not e
t h a t at t h e e n d o f e ac h p e r io d , Dg
in t h e t h inned s t an d is great e r t h an
t h at o f a l l merchan t ab l e t r e e s i n
t h e unt hi nn e d s t an d .
At t h e en d s o f
t h e f i r s t two i n t e r v a l s ( ag e s 3 2 and
40 ) , howeve r , t re e s in t h e t h in n e d
st and are sma l l e r t h an t h e s am e
numb e r o f larg e st tre e s i n t he
un t h i n n e d s t an d .
At t h e end o f the
t h i r d i n t e rva l , equal numb e r s of the
l ar ge s t t re e s are n e ar l y the s ame s i ze
in t he two s t an ds .
Th ere a f t e r , equal
numb e r s o f the l ar ge s t t r ( ", s are a
l i t t l e l ar g e r in t h e t h i n n e d s t an d
t h a n i n t he unt h in n e d s t an d .
15
THINNED STANO
UNTHINNED STANO
400
300
"
OJ
OJ
....
200
W
100
OJ
(.
In
J
crIII
rr
[j
<J:
80
w
SO
rr
Q.
<J:
w
rr
<J:
.J
<J:
{f)
<J:
ill
40
30
20
SOD
400
300
100
2CC
80
SO
50
40
NUMBER OF TREES PER
30
20
10
8
ACRE
Fiqure 19.--Rel a tive development of thinned
and un thinned stands, by number and si ze
of rees a t specifi ed a ges .
Num ber of Trees
The number of t rees wh i c h a t t a i n
a s pec i f ie d min imum d . b . h . i n average
n a t ural s t a n ds i s assumed in dependent
of s i t e i n dex ( f i g. 5B ) .
In s t an ds
p recommerc i all y th i nned to the des i red
number o f t rees , t h e number reachi n g
a spec i f i ed min imum d . b . h . will b e
If
t he s ame a s f o r n at ural st ands .
we begin commercial t h i n n i n g a t t h e
f ir s t po s s i b l e age , all these mer­
chant able t r ees wi l l be harves t ed .
Number o f Trees at F i n al Harvest
The part o f this total number
o f t r ees wh i ch will be carr ied t o
f i n al harvest varies w i t h s i te
16
qua l i t y , r o t a t i o n age , a n d s t and
For our selected
t reatment reg ime .
t h i n n i n g reg i mes , number at f inal
harvest ran ges from 1 3 to 4 5 percent
of t he t o t al i n i t i al number o f
merchan t ab le t r ees ( t able 2 ) .
Thi s
r el at i ve number a t f i n al h arvest
increases with decreas i n g s i t e
qual i t y an d i s l es s for s t an ds
t hat were precommer c i ally t hinned
t h an f o r those that were not .
Re l a t i ve to unt h i nned s t an ds of t he
s ame s i te and age , t h inned s t an ds
have about 50 to 75 per cen t as many
merchant able t rees to be cut at
f in a l harves t .
The smallest rela­
t i ve number is in good s i te , p re­
commerc ially t h i n n ed s t an ds , and
the greatest i s i n poor s i t e
st an ds that were n o t precommer c i a l l y
th inned .
rab e 2 - -Nwnbe1' IN), avemge d. b . h . IVg) , and basal area ::>el' ac1'e IC) of 'ne1'oncmtab l e tl'ees B. O inches
'
and ZaPger in d. h. h. at fina l harvest of thinned st::mds, and their l'e Zc.tionship -;0 tot;al
yi'e ld of thinned stands and to live stand ay; ;';,na l harvest of unr;hinned s tand8
S i te
Age
Current
thi nned stand
Treatmentll
N
Og
I
I n c h es
Years
I
I
G
Square
Re l a t i v e to
unthi nned stand
Percent of total
y i e l d of thi nned stand
I
I
N
G
.. .. .. .. .. ..
N
I
\
Og
G
- - Percent -
85
CT al one
P C T + CT
60
53
28 . 2
31.0
263
277
15
13
56
55
56
50
122
134
85
89
II
90
CT a l one
PCT + CT
78
66
23 . 8
26 . 8
240
256
19
16
58
56
60
50
118
133
83
88
III
95
CT a l one
PCT + CT
107
84
19 . 3
22.6
216
234
27
21
61
58
64
50
114
132
82
88
IV
100
169
1 17
14 . 4
18. 1
191
210
42
29
66
62
74
51
105
132
81
89
V
105
CT a l one
P C T + CT
180
13 . 5
178
45
67
54
1 30
90
PCT + CT
N per acre X 2 . 4 7 1 = N per h a ;
Metr c conver s i on :
G i n feet p e r acre X 0 . 2296 = G i n m2 p e r h a .
11
C T i s cornne rci a l thi n n i n g ; P C T
is
Og
in i nches
X
2 . 54 =
Og
i n centimeters ;
preconrnerc i a 1 th i nn i ng .
; OO
D i s t r ibut ion o f Tree s Over Time
Merch ant ab l e t r e e s not r emain i n g
for t h e f inal harvest h ave b e e n
removed in comme r c i a l t h in n i n gs
( f ig . 20 ) ,
Many t r e e s are r emove d
at t h e f ir s t t h i nn i n g , an d p r o g r e s ­
s i ve l y f ewer a t e a c h succe s s i ve
t h i n n in g .
St ands on good s i t e s
r e c e i ve more t hinn i n g s t han t h o s e
o n poor s it e s ; s t an d s that were
pre comme r c i a l l y t h in n e d rece ive
mor e t h i n n i n g s t h an those wh i c h
were n o t p r e comme r c i a l l y t h i nn e d .
The numb er o f me rchantab l e t r e e s
in t h e unt h i n n e d st an d i s gre a t e r
a t e ach age .
D i am et e r of Trees
D i ameter at F in a l Harve st
As a coro l l ary to numbe r o f
t r ee s , t h e D g o f t r e e s at f i n a l
harvest ranges f r o m about 5 t o 3 5
p e r c ent l arger in t h in n e d st ands
t h an the ave r a g e of all merch ant ab l e
t r e e s r ema i n i n g i n un t h i n n e d s t an d s
( t ab l e 2 ) .
The g r e at e st di f f e r e n c e
i s in st ands t h at h ave b e e n p r e c om­
me r c i a l l y t h i nn e d .
When we comp are
D g of r e s i du a l t r e e s in s t an d s wh i ch
we r e o n l y comme r c i a l l y t h i n n e d w i t h
t h o s e o f t h e s am e n um b e r o f l ar g e s t
t r e e s i n natural s t an d s , howe v e r ,
we f in d t hat t he y are s imi l ar
( f ig . 19 ) .
I n p r e aomme r a i a Z Z y
t h i n n e d s t ands , t h e Dg o f t r e e s
650 SITE I I A
\
\
\
\
\Tltll Und
\
\
\
6+ \
\
inchU
\
600
550
500
:
\\
350
300
,
,,
,
...
250
200
...
....
...
1 50
w
a:
II
a:
w
...
...
,,
1 00
50
O
o
700
[:'
650 f-
IJHTHIHHED
COfi,4MEflCIAl
THINNING ALONE
L-L-L10
20
J-
30
B
-L
40
-L
50
SITE IV
\
\
600
550
500
450
\
,
\
\
\
L-__
250
200
90
1 00
\
\
------" " " " " " " ',
UHTHIHNED
1 50
COMMERCIAL THIHNIHG AlOHE
1 00
50
80
\
\
\
\
350
300
70
\Tm! SIM4
6+
400
80
P'RECOMMERCIAl HIIHHIHG
COfi,4MERCIAl THINNING
I
__LL-L-L-
PRECOMMEIICII.L THIHNIHG
+ COMMERCIAL THIHNING
O �L-L-����J--L-L-LI�I�!�I����I�I�!��!
o
10
20
30
40
50
T01'AL /J .G E \
60
{yeers}
70
80
90
100
Figure 20 . --Trends of number of trees over
time :
A , Si te II; B, Si te IV.
17
!,
wi l l general l y be 1 0 to 15 p e r cent
l ar ger t h an the D g of the s ame
numb er of l argest t r e e s in un th i n n e d
s t an ds .
I n creased growth o f r e s i d­
ua] t rees is mor e or l es s o f f s e t
b y t h e removal o f some larger th an
average t re e s in t h i nn i n gs-- t rees
wh i ch wou l d o herw i s e b e present
at f i nal harve st .
Tren ds Over Time
The increas e in Dg ove r t ime
r e f l e c t s a comb in at i on o f growth o f
surv i v i n g t rees a n d l o s s o f t r e e s
from t h e s t an d .
The r e fore , t h e
t r e n d over t ime i n t h inned s t an ds
i s qu i e d i fferent f r om that in
un t h inned s t ands ( f i g . 2 1 ) .
I n an
un t h i nn e d s t an d , t h e i n cr e a s e in D g
o f merchan t ab l e t re e s progr e s s e s
smoot h l y o ve r t ime--on a s t e a d i l y dec l i n i n g numb e r o f t r ees ; t h e i n c r e as e i n D g i s great e r t han t h e d . b . h . growth o f survi v i n g t r e e s .
I n t h e t h i n n e d s t and , t h e re i s an
abrupt i n c r e a s e in Dg e ach t ime
t h e s t an d is t h i n n ed ( i f diD is
l es s than 1 . 0 ) ; the i n c r e a s e be tween
t h i nn i n gs is the actual growth o f
survivors .
On good s i t es t h e gain in D g
b e c au s e o f commer c i a l t h i n n i n g is
gre a t e r than t h e addi t i o n al gain
from pre comme r c i a l t h i nn in g .
On
poor s i t e s , the revers e i s true .
The d . b . h . growth rat e with com­
me r c i a l t h i n n i n g alone is ver y
c l o s e t o t h e r a t e o f i n cr e ase i n D g
o f merchan t ab l e t rees i n t h e n a t u r al
s t an d ; -- a l i t t l e b e t t e r on good
sites .
D i amet e r growt h rate wi t h
p r e commerc i a l t h i n n i n g is always
a l i t t l e bet t er than with comme r ­
c i al thin n i n g a l on e .
SITE "
Effects of Al t ern at e Thinning R eg i m es
M i n imum Merchan t ab l e D . b . h .
!
,
!
j
!
)
70
I
I
30
1
,
80
I
100
SITE IV
20
18
16
14
The l ar ge r t h e min imum merchant ­
ab l e d . b . h . ( dm ) is , t h e fewer and
t h e l arger are the t rees harves t e d
( t ab l e 3 ) .
The e f f e ct on t h e f in a l
harvest is f a i r l y minor .
With
only commer c i al t h innin g , a l arger
dm t ends t o r e s u l t in s Zight Z y mor e
t re e s an d sma l l e r t rees a t f i n al
harve s t ; in p r e commer c i a l l y t h i nn e d
st ands , t he r e v e r s e is t rue .
The
maj or e f f ect is on t r e e s removed
in t h inn i n gs .
With a l a r ge r dm ,
a much sma l l er number o f t re e s i s
remov e d ; a s a r e s ul t " t h e Dg o f
b o t h t h e t r ees harve s t e d i n t h i n ­
n in gs a n d al l t r e e s harve s t e d is
l ar g e r .
12
10
t
0
D e l ayed First Thi n n in g
I
10
I
\
20
t
!
30
I
!
40
•
!
50
!
,
80
I
TOTAL AGE ( yeat"'S)
[
70
!
!
!
30
Figure 21 . - -Trends of Dg over t:ime :
Si t:e II; B , si t:e IV. 18
I
,
80
I
100
A, The e f f e c t o f de l a y i n g t h e
f i r s t commer c i a l t h i n n i n g i s s i m i l a r
Fewer l i v e t re es
t o t h e f o r e go i n g .
wi l l b e av i l a b l e for harvest in
t h i n n i n g s ; howev e r , p art o f t h i s
l o s s c an be o f f s e t b y sal vage o f
r e c e n t merchan t abl e mor t a l i t y
Growth rat e s o f mer­
( t ab l e 4 ) .
ch a n t ab l e t r e e s w i l l b e r e duc ed
somewh a t dur i n g t h i s de l ay p e r i o d ;
IDg)
Tab l e 3--/lumbe"l' (N) and ave"l'age d. b . h.
of t,.., e8 ha:rvested in e<Xrme"l'cnaZ thi7l1li7l{1B
finaZ ha:rvest, by Bite, treatment, and minimum TTl€1"ehantab Ze d . b . h . (dm)
S i te
I
CO/TlJonen t a n d dm
II
S i te
II
1 09
I
II
I nc h e s
Og
I
I
S 1 te
III
II
I
I nches
S i te
V
S i te
IV
l ug I
1 09
N
I nches
and at
N
1 09
I nches
I nches
ONLY COMMERCIAL TH I NN I NG
6 . 0+ i nches :
Thi n n i ngs
F i n a l harvest
Tota l number of trees
343
60
403
10 . 6
28 . 2
14 . 6
327
78
405
10 . 0
23 . 8
13 . 8
295
107
402
9.3
19 . 3
12.8
235
169
404
11.4
225
64
289
12 . 1
27 . 3
16 . 7
207
82
289
11.5
23.0
15.6
176
113
289
10 . 9
18 . 5
14 . 3
116
172
288
10. I
14 . 2
12 . 7
284
1 17
40 1
9.2
18.1
12.5
222
180
402
8.5
13.5
11.0
176
10 . 9
18.7
161
1 26
10 . 2
14 . 4
287
12.7
8.6
14 . 4
7 . 5+ i nches :
Th i nn i ngs
F i na 1 harvest
Tota l number of trees
PRECOMME RCIAL TH I NN I NG + COfotIERCIAL TH I NN I NG
6 . 0+ i nches :
Th i nn i ngs
F i na l harvest
Tota l number of trees
349
53
402
10 . 9
31.0
15.2
336
235
52
287
12 . 8
31.1
17 . 6
222
65
-287
66
402
10 . 4
26 . 8
14 . 4
402
9.8
22 . 6
13.5
12 . 1
27 . 1
205
82
ll.5
22 . 9
III
16 . 7
287
15 . 7
287
318
84
7 . 5+ i nches :
T h i n n i ngs
F i na 1 harvest
Tota 1 number of trees
Hetri c convers i o n :
II
per acre
Og
X
in inches
2 . 471
X
2 . 54
II
=
pe r h a .
Og
=
14 . 4
in centi me ters . T a b l e 4--Numbe1" (N) and average d. b . h . (Dg) of merahantab Ze Zive trees
1"emaining if thi.7I1Ii.ng i. de Zayed, and aorrespcmding pe1'i<xi.ic
r"hantabZe d. b . h. 1.0
merehantabZe mo1"taLity, when minimum
6. 0 inaMs
....
S i te
Fi rst
po s s i b l e
age for
thl nnlng
HUI!tler of years d e l ayed
0
H
1 09
J
H
.!2s
Years 30
20
10
lXi
N
Inches
I
Og
H
I nches
I
ll9
I nches
LIVE TREES
I
II
III
IV
V
25
30 36
47
68
403
405
402
403
403
8.0
8. 1
8.0
8. 1
8.0
312
333
362
382
DEAD
I
II
III
IV
V
25
30
36 H
68
0
0
0
0
0
Ketri c conyers i o n : 11 . 0
10 • •
9.7
9.2
H
per a c re
X
13.8
12.7
11. 4
10 . 4
176
206
2048
16.4
14 . 8
13.0
85
76
65
46
8.3
7.9
7.4
7.2
50
50
10 . 1
.9.3
11 . 4
TREES
91
72
40
21
lXi i n i nches
227
256
297
336
6.8
6.7
6.8
7.2
2 . 47 1
X
2 . 54
H
•
•
49
per hectare . Il9 in centllneters . 19
f urt hermore , t h e y wi l l c o n t i n u e t o
b e lo we r a f t e r t h i n n i n g than i f
t h e s t an d h a d b e e n t h in n e d ear l ier-­
t h e l o n g e r t h e d e l ay , t h e gre a t e r
ehe loss .
Fr eque n c y and S e v e r i t y o f Thinn in g
Redu c i n g t h e average growin g
s t ock l e v e l l e ads t o f ewe r and
l arger t re e s at f i n al harve s t ;
i n c r e a s i n g the average level l eads
t o mo re a n d smal l e r t rees at f i n al
harvest .
R e l at i n g t h i s to t h e
n at ur a l s e and curve i l l u s t r a t e s
h ow D g ae f in a l h a r v e s t o f t h e s e
t h in n e d s t an ds compares wi th t h a t
o f t h e s am e n umb e r o f Zarge s t tre e s
i n t h e un t h i n n e d s t an d ( f i g . 2 2A ) .
Dg o f t rees remo v e d in t h i n n i n g s
i s g r e at e st i n t h e s t an d main t a i n e d
at a h i gh aver age l e v e l a n d l e ast
i n t h e s t an d main t a i n e d at a l ow
average l ev e l , but di f f e rence are
smal l .
'i3"
Q)
.2!
!
lJ
'" [
ill
(L
300
200 50
1
1
::
so
li:
Og (lncnesj
'" ill
[
'" Type o f Th i n n i n g
The h i gh e r t h e d i D r at i o i s a t
t h e f i r s t D o s s i b l e comme r c i al t h i n ­
n i n g , t h e g r e at e r t h e numbe r o f t rees
an d t h e sma l l er t h e average d . b . h .
o f t r e e s rema i n i n g at any t im e
( f i g . 22B ) .
Th e r e l at ive d i f f e r e n c e
d e cr e a s e s with e ach succ s s i ve
t h in n i n g .
Thus , d i f f e r e n c es , both
at f i n a l h arve s t a n d ave raged over
the r o t a t ion , tend t o de c r e a s e with
i n c r e a s i n g site qua l i t y and t o b e
l es s i n s t ands that are p recommer ­
c i a l l y t h i n n e d t h an i n t h o s e that
are n o t .
VO L U M E Y I E LD
G ains i n Tot al M er ch an t a b l e Pro d u ction
G a i n s in merch a n t ab l e produc­
tion depend on mer ch an t ab i l i t y
s t an dards , a s well a s o n t h e age at
Th e r e ­
whi c h comp ar is o n s are made .
fore , t o i l l us t rat e t h e b as i c e f f e c t s
o f t h i n n i ng , w e f i r s t exami ne r e l a ­
t io n s h i p s i n t e rms o f cub i c vo l ume
To provide
of t o t al s t em ( CVTS ) .
p e r s p e c t i v e r e gardi n g t h e e f f e ct of
a ge , we compare max i mum me an annual
i n creme n t s ( m . a . i . ) , regardl e s s of
20
400 300 200
NUMBER
OF
TREES
100
PER
eo
so
ACRE
40
Figure 22. --Effects of al terna t e thinning
regimes on number and size of trees :
A , Al t ernat e s tocking and thinning in terval ;
B, al t erna te type of thinning (diD regime) .
ages at wh i ch t h i s culmi n a t ion o c cur s ; w e then i l l us t r at e t h e e f f e c t s o f maki n g comp a r i s o n s a t other ages .
We t h e n examin e gains at our s e l e c t e d r o t a t i o n ages by various measures of mercha n t ab l e p r o duc t i o n . Culmi n a t i o n o f m . a . i .
Wh en d o e s m . a . i . culmin a t e ? A n y p r act i c e o r merchan t ab i l i t y s t andard t h a t i n c r e as e s merch ant ab l e p r o duct ion ear l y i u t h e r o t a t io n . more t h a n t owar d t h 0 e n d wi l l r e du c e t h e a g e at wh i ch culminat i o n o c curs . 330
C o n v e r s e l y , anyt h i n g t h a t i n c r e as e s
mer chan t ab l e produc t ion l at e r rather
t h an e ar l i er in t h e r o t a t ion wi l l
i n c r e as e the age o f culminat ion .
Thus , whe reas g r o s s m . a . i . in
t e rms of t o t al s t a n d CVTS culminat es
at about age 63 on a l l s i te s , mer­
chant ab l e m , a . i . c u l m i n a t e s l at er
on p r o g r e s s i v e l y p oo r e r s i t e s --ran g i n g
f r o m about 6 5 y e ar s o n s i t e I t o 1 0 5
y e ar s on s i t e V .
T h i n n i n g s r e duce
the ages at wh i ch mer ch an t ab l e
m . a . i . c u lm i n at e s ; t h us , culmin a t i on
a g e s i n s t ands r e c e i v i n g e ar l y pre­
comme r ci a l t h in n i n g range f rom about
65 to 85 years on s it es I through V .
B o a r d - f o o t m . a . i . culminates at
l at er a g e s t h an cub i c - fo o t m . a . i .
O n e s h o u l d f ir s t have a c l e ar
und e r s t an d i n g o f t h e r e l at i o n s h i p
o f m e r chan t ab l e y i e l dZl t o t o t al
y i e l d in natural s t an d s ; t h e n one
s ho u l d compare m e r oh a n t ab Z e y i e l ds
wi t h a n d without t h i n n i n g .
At ages
of m a ximum m . a . i . , t o t al gro s s
y i e l d in unt h inned s t ands i s abo ut
3 8 p e r cent g r e at e r t h an net y i el d .
The p o r t ion o f t h i s g r o s s y i e l d
con t ai n e d i n mer ch an t ab l e t re e s -­
6 i n ch e s ( 1 5 cm ) d . b . h . and l ar ger-­
i s abo u t 8 to 33 p e r c ent l e s s t han
t o t al g r o s s y i e l d on s i t e s I
t h r o u gh V ( f i g . 2 3A ) .
M e r ch an t ab l e gro s s y i e l d o f
s t an ds r e c e i v i n g o n l y comme r c i a l
t h i nn i n g i s l e s s t h an t h at o f
unt h i n n e d s t an ds ( f i g . 2 3B ) .
Th is
is a r e s u l t o f the r e du c e d growth
p e r a c r e wh i ch o c c u r s be tween f i rst
t h i n n i n g and f in a l harvest .
Th i s
l o s s i s , g e n e r a l l y , cons i de r ab l y
l e s s t h an t h e mer c h an t ab l e v o l ume
o t he rw i s e l o s t to mo r t a l i t y ,
howev e r .
Y i e l d of p r e comme r c i a l l y
t h in n e d s t an ds is a l so l e s s than
t o t a Z gro s s y i e l d of un t h inn e d s t an ds ,
but n o t as much so .
A l l pr e c om­
mer c i a l l y t h i nn e d s t an d s r e c e i ve
a l a s t i n g b e n e f i t f rom concent rat i n g
growt h o n t o merchan t ab l e t r e e s .
11
I n terms of CVTS ,
y ield refers
trees .
to
CVTS of
merchantable
merchantable size
A
30e :-
270
t:-
240
f:..
2 10
[
r
"o
1 50
1 20
80
80
W
:;:
Cub i c Vo l ume o f To t a l S t em
r
3
33
0
t
"
k
,..
t
o
'
80
0
[
;
"
270
240
2 10
3
!
!
100
t
b
'
80
!
!
120
!
!
!
1 40
1 80
,
1 80
!
200
MERCHANTABLE GROSS m.•.!.
WITH PRECOMMERCIAL THINNING
... COMMERCIAL THINNING
I­
:t
!
8
00
..J 3
z
!
!
!-L
! _'
100
!-L
! !-L
! !-L
' !
120
!-L
! !-L
! !-L
! !
140
INITIAL SITE INDEX
1 60
! -L
!
1 80
L
! !
200
(100-yesl""basls)
Figure 2 3 . --Mean annual incremen t of cubic vol ume of total s t em (CVTS) at time i t culminates , when minimum merchan tabl e d. b . h . is 6 . 0 inches :
A , Merchantabl e m. a.i . relative to total m. a .i. in un thinned s tands ; B, merchantable m . a .i . wi th commercial thinning rela tive to that without thinning.
The add i t ional b e n e f i t a s s o c i a t e d w i t h imp r o v e d h e i ght growt h
i n c r e a s e s with d e c r e a s i n g s i t e qua l i t y . At ages o t h e r than culmin a t i o n
o f m . a . i . , r e l a t i ve y i e l d s are
somewhat d i f f e rent from t h o s e
21
j
l;
,
:
I r:
1 ["
J
I ·
; !.
di scus s e d above ( f i g . 24 ) . At ages
pr io r t o culminat ion , di f f e r e n c e s
i n m . a . i . b etween pre comme r c i a l l y
t h inn e d s t ands and t hose r e c e i v i n g
o n l y comme rcial t h inning a r e a
l i t t l e great e r ; at ages l at er t h an
culmin a t ion , d i f ferences in m . a . i .
Prior t o culmina­
are a l i t t l e l e s s .
t ion , d i f ferences in mer ch ant ab l e
y i e l d b e tween un t h i nned s t ands and
comme r c i a l l y th inned st ands are l e s s ;
a f t er culminat ion , d i f f e re n c e s are
greater .
The rot at ion ages we have
chosen for our e xamp l es are about
2 0 years beyond culminat ion o f
merchantab l e CVTS in precommer c i a l l y
t h i nn e d st ands , b u t sub s t ant i a l l y
ear l i er t h an culmin ae ion o f m . a . i .
in t erms o f board-foot vo l ume .
For
t h e remainder o f t h i s s e c t ion , a l l
compari sons are b ased o n t h e s e
chosen rot at ion ages .
Ga i n s b y D i f f e r en t
Produ c t ion
easures o f
Mean annual incremen t s by f i v e
me asur e s o f mer c hant ab l e produce i o n
are shown in t ab l e 5 f o r t h e s e l e c t e d
r e g ime s .
Th i s t ab l e is i n t e n d e d t o
p r o v i de t h e r e ader w i t h s ome s p e c i f i c
e s t ima t e s o f y i e l d , a s we l l a s p r o ­
vi d i n g b ackground for sub s equen t
d i s cuss ion .
anm...a t inaPemlmt at speoified potation ages, by site,
!:reatment, and VariOU8 meaSUl"es of productionJ' trees D . O
inohes and "larger i n d . b . h.
Tabl e 5 ..-Mean
Measure of prodUc!ionY
Site t age. and treatment
Site
r.
CVTS
Square
feet
•
.
! CY4
Cubic · ·
feet
SV6
IV5
•
•
Board · feet
B5 years:
3 . 65
3.87 5 . 55
5 . 92
215.8
227 , 8
278.4
289 . 3
212.2
224 , 0
270. 1
280.7
1546. 1
1627 . 1
1863 . 5
1947 . 7
139 7 ,
1466.
16J6 .
1728.
3.22
3 . 40
4 . 54
5.03
170 . 4
179.2
214.2
228.9
167 . 3
175.9
207 . 1
221.5
1175.9
1231. 7
1376 . 4
1490 . 4
104 5 . 3
109 1 . 5
1 182. !
1300. Z
Unthinned
Unthinned plus sal vabl eY
Conrnerc ial thinning alone
PrecOll111e rcial thinning +
cOll111e r cial thinning
Site I V , 1 0 0 years:
2.79
2 . 94
3. 75
4 . 21
129. 0
135.2
155 . 8
176.5
125.7
131.6
149. 5
169.9
832 . 0
867.2
939. 3
1095. 3
714.5
741 . 7
i78 . J
931.3
Unthinned
Unthinned plus sal vabl "y
COll111e rcial thinning a l one
Precorrrne rcial thinning +
corrmerciaJ thinning
2 . 36
2 . 47
2. 87
3 , 41
91. 6
95. 6
103 . 8
128 . 7
87. 9
91.6
98. 1
122 . 7
528.2
547 . 4
565. 8
744 . 6
427 . J
440 . J
436. 9
607 . 9
1 . 88
1 . 95
2 . 52
57 . 7
59. 6
82 . 4
53.6
55 . 3
7 7. 2
276.8
284. 1
426.9
189. 4
192.9
320.6
Unthinned Unthinned p l us sal vabl eY
Canmereia 1 thinning al one
Preconmercial thinning +
corrmerci a 1 thi nnin9
Site I I , 90 years:
Unthinned
Unthinned plus salvabl eY
COll111ercial thinning alone
Precomnercia 1 thinning +
canmercial thinning
310 280
Site I l l , 95 years:
270 250
;; 230 •
.!!
.Q 2 1 0 .0
B
Iz
i
SITE / I
wtln
+
1 80
1 70
orecommefCIal HlInnrng
com
caaJ thinning
UNTHINNEO STAND,
GAOSS m.a.1
Witn commercIal
:hlnnlng only
1 50
Site
VI
105 years:
Unthinned
Unthlnned plus salvabl eY
Preconmercia 1 thinnin9 +
cOll111e r oia 1 thinning
Metri c conyersi6n : 1 30
G in square feet per acre
meters per hectare.
CV in cubic feet per acre
meters per hectare.
X
X
0. 2296
=
0.0 700
=
G
in
SQU'N!
CV in cubic
Y G = basal area; CVTS = cubic volume of total stem; CV4 = cubic
volume to a 4-inch (lO-cm) top d . i . b . ; IV5 • l nternationa 1 board- foot
vol ume to a s-inch ( l3-on) top, 1/4-inch kerf; SV6 = Scribner board-foot volume to a 6-inch ( IS-em) top (Scribner volume is the fonnula version appl ied to 16- foot l ogs ) . CV4 , I V 5 . and SV6 excl ude vol ume in the stumP . Y For this comparison, a l l mercnantab l e roo rtality occurring within
10 years of final harvest is assumed to be salvable at final harvest.
1 10
80
70
50'��������-J�
30
40
50
60
70
80
80 1 00 1 1 0 1 2 0
STAND AGE
(yea""j
Fi gure 2 4 . --Mean ann ual incremen t of merchant ­
able cubic vol ume o f total stem (CVTS) a t
ages before and after culmina tion, when
minimum merchan table d . b . h . is 6 . 0 inches .
22
To p r o v i d e r e a l i s t i c e s t imat e s
o f ga ins from t h i n n in g , w e h ave
added e s t imat e s of sal v ab l e mor t a l i t y
t o t h e l iv e vo l umes harve s t e d f rom
un t h in n e d s t ands .
Th i s is the
e s t imat e d merchan t ab l e mort a l i t y
wh i ch o c curred dur in g t h e 1 0 - year
per i o d p r ior t o harves t .
The
amount t hat t h i s s a l vage adds to
t o t al usab l e product ion d e c r e as e s
with de c r e as i n g s i t e qual i t y an d
wi th measures o f merchan t ab l e
v o l ume wh i ch exclude progres s i ve l y
mor e o f t h e t o t a l vo lum e .
Th e correspon d i n g p e r c e nt a g e
and ab s o l ut e gains i n CV4 y i e l d are
i l l us t r at e d in f i gure 2 5 .
Gains
f rom o n l y comme r c i al th i n n i n g are
great e s t on good s i t es , whe r eas
t h e additio n a Z gains f rom p r e com­
m e r c i a l t h i n n i n g are greater on
p o o re r - t h an - average s i t e s .
With
our as s umpt i o n s , t h e maximum
i n c r e a s e in CV4 m . a . i . due t o
p r e comme r c i a l t h i nn in g o c curs a t
about s i t e i n d e x 1 00 .
R e l at ive
ga ins b y other me a s u r e s o f v o l ume
p r o duct ion are shown in t ab l e 6 .
so
iab l e 6 --Gaine
in mean annual. incremen t to Bpeaified potation ageB,
oue m asUl'e of production; 'trees a. 0
by 81- te and !J
inanss and larger in d.b. h.J
!
Measure of producti onY
Site, age, and trea tment
CVTS
ABSOLUTE GAIN
Square
S i te I , 85 years:
Coomerc i a l thinning a l one
Precoomercial thinning +
comnere i a l thinning
Oi fference 11
S i te I I , 90 years:
Coomerc i a I thinning a lone
Preccnmercial thinning +
coornerc i a l thinning
Oi fference 11
S i te I I I , 95 years:
Conmercial thinning a l one
Precoomerci a l thinning +
conmerc i a l thinning
Di fference 11
S i te IV, 100 years :
Conmerc i a l thinning a l one
Precoomerc ial thinning +
coomerc i a l thinning
Di fference 11
Site Y. lOS years:
Conmerc i a l thinning a l one
Precomnerci a l thinning +
coomere i a l thinning
Di fference 11
S i te I , 35 years:
Conmercial thinning a l one Preccmnerci a l thinning + conmerci a l thinning
Di fference 11
S i te l l , 90 years :
Conmereial thinning a l one
Precocrmerci a l thinning +
conmerc i a l thinning
Di Herence 11
Site I I ! , 95 years :
Canmercia 1 thinning a lone Precoomerc i a l thinning + corrmerci a l thinning
Di fference 11
Site IV, 100 years :
COlmlereial thinning a l one
Precoarnerci a l thinning +
conmere i a I thinnino
Di fference 11
S i te V, 105 years :
Comnereial thinning a l one
Precanmerci a I th i nni ng +
conmercia I thinning
Di fference 11
I
SV6
CV4
- - Cubic - feet
- - Board feet
1 . 6B
2 . 05
50 . 6
61.5
46. 1
56 . 7
236
321
170
262
. 37
10 . 9
10 . 6
B5
92
1 . 24
1 . 63
35.0
49 . 7
31.2
45.6
145
259
91
209
. 39
14 . 7
14.4
114
1 18
.81
1 . 27
20. 6
41.3
17.9
38 . 3
72
228
37
190
. 46
20 . 7
20 . 4
156
153
. 40
. 94
8.2
33. 1
6 .5
31 . 1
18
197
- 3
168
. 54
24 . 9
24 . 6
179
171
.57
22.8
21. 9
143
128
.57
22.8
21.9
143
128
PERCENTAGE GAIN
- Percent 43
53
22
27
21
25
15
20
12
18
20
27
18
26
12
21
8
19
10
36
48
10
11
5
28
43
15
31
14
29
8
26
26
16
15
14
17
21
16
38
9
35
7
34
3
36
- 1
38
22
26
27
32
39
29
38
40
50
66
29
38
40
50
66
1/ Ga ins are relative to unthi nned plus s a l vabl e (from tab l e 5 ) .
Y G = basal area; CVTS = cubic vo l ume of total stem; CV4 = cubic
INITIAL SITE INDEX [100-yeBr-bBsis)
vol ume to a 4-inch ( IO-em) top d . i . b . ; IV5 = lnterna tional board-foot
vol une
a s-inch ( I3-cm) top, 1/4-inch kerf; SV6 = Scribner board-foot
volume to a 6-inch ( I S-em) top (Scribner vol tll1e is the fonnula vers ion
appl ied to 16-foot 1 09S ) . CV4, IV5, and SVG exclude vol ume in til. stump.
11 Di fference between precOOTIl(!lx i a l thinning + co",, rcial thinni g
and comnerc i a l alone is gai n due to precomnerc i a l thi nning.
Figure 2 5 . --Gains in mercha n tab1.e cubic vol ume
(CV4) due to thinning:
B, percentage ga ins .
A, Absol ute gains ;
23
o t e that r e l a t i ve gains from
comm e r c i a l t h in n i n g decrease as
l e s s of the t o t a l vol me in mer ­
cha n t ab l e t r ees i s deemed usab l e ;
t h at is , gr e at e s t for CVTS and
l e ast for SV6 .
Th e t r end for
add i t ional gains f rom p re comme r c i a l
t h i n n i n g i s t h e reverse ; l e a s t f o r
CVTS an d gre a t e s t f o r SV6 .
R e l a t i ve
gains on d i f f e r e n t s i t es a l so vary
wi t h the measure o f produc t i on ;
however , b y a l l measures , the ,
'
ab s o l u t e gain f r om p r ecomme r c i al
t h i n n i n g is great e s t on s i t e I V .
D i st ri bution o f Yi el d s Over Tim e
Th e ac cumul a t ion o f t o t a l
y i e l d o v e r t ime an d t h e d i s t r ibu­
t ion of this y i e l d amo n g thinn i n g s
and f in a l harve s t , f o r t h e s e l e c t e d
regime s , a r e i l l u s t rated i n f i gures
2 6 - 2 8 f o r s i t e s I I and I V in t e rm s
t
SOO
450
400
SITE I I
A
22
r
I
SITE I I
A
18 r
16
20
iJrlhll fO
14
"68 :t
10
W
a:
u
«
0
a:
w
6
a. 1
w
:J
:1
F
14
..J
5+ 0IIC1'ln
I
8
:0
I
I
20
,
I
30
,
I
40
I
I
50
I
I
80
I
70
SITE IV
I
8
I
0
I
I
I
I
80
1 00
80
lOC
0 12
>
8
6
10
4
2
L
L
350
24
0
0
300
10
20
30
TOTAL AGE {years)
40
50
8e
70
8
0
Figure 27 . --Trends of cubic vol ume (CV4)
A , Site II ;
production over time :
B , site IV.
250
200
1 50
100
50
0
0
400
LO
20
30
40
50
60
70
80
80
1 0C
SITE IV
8
350
300
UM 'Mn!O
250
200
150
1 00
50
0
a
10
20
30
AGE ( years)
40
50
60
70
80
80
1 00
Figure 26 . --Trends of basal area production
A , Si te II; B , Si te I V .
over time :
24
o f b asal a r e a , CV4 , and IV5 .
The
t o t a l - y i e l d curves i n these f i gur e s
suppl ement t h e f o r e go in g d i s c ussion
an d further i n d i c a t e r e l at i ve g a i ns
i n y i e l d w i t h s ho r t e r rot a t i on s .
Th e fol lowing d i s cu s s ion wi l l focus
on the r e s i dual s t an d- -b e f o r e a n d
a f t e r each cut t i n g .
A t t ent ion
is dir ect e d f i rst t o the vo l ume
r ema i n i n g f o r t h e f in a l harve s t
an d then to vo l ume r emo ved in
t hi nn i n gs .
�---
r
:
-�---.
SITE I I
A
l :J C l 2Q
L
:
L
,
,
7
F
0
SO
SC
4C
:J C
O" O
D
t
!
I
I
r-
L
L
l
f
•
i
:
!
I
00
80
3C
7
0
60
2
1
Fi
�-�-----��--
f
10
,
'
20
,
I
30
40
I
!
SO
SITE IV
,
I
SO
,
I
70
,
I
80
,
!
J
90
I
1 00
B
Vo l um e Remo ved in Th i n n i n g s
:- I I
L-,''--.J1--'-l'--.JI-----1--:-1:':-'-' ' :-'-1-:::1:-'""' -:,-::1-"-,;;,;:::' ' ;::,;:' .,.J
Q
ure
c omme r c i a Z t h i n n i n g , t h i s vo l u me
at f i n a l h a r v e s t i s about 8 5 p e r c e n t
o f t h e vo l ume o f l i v e me r chan t ab l e
t r e e s i n n a t ur a l s t a n ds o f t h e s ame
s i t e and age .
Th i s r a t i o i n c r eas e s
s l i gh t l y w i t h i n c r e a s i n g s i t e i n d e x
an d is s l i gh t l y g r e a t e r f o r b o a r d ­
f o o t vo l ume t h an f o r cub i c - f o o t
v o l um e .
F o r s t ands t h a t w e r e
p e c o mm e r c i a Z Z y t h in n e d , t h i s r a t i o
o f vo l ume a t f in a l h ar ve s t t o f i n a l
vo l ume o f comp a r ab l e n at u r a l s t an ds
i n c r e ases wi t h d e c r e a s i n g s i t e
qual i t y and , e s pe c i a l l y o n poor
qu a l i t y s i t e s , i s s ub s t an t i a l l y
g r e a t e r for b o ard- f o o t vol ume t h an
f o r cub i c - f o o t vo l ume ,
On poo r
s i t e s , b o ar d - f o o t vo l ume at f i n a l
harve s t ( as we l l as t o t a l produ ct ion )
is gre at e r t h an t h at in comp a r ab l e
un t h i nn e d s t an d s .
10
2C
30
2 8 . - - Trends
prod uction
4C
SC
TCTAL AGE
SO
( years 1
70
of board-foot
over t i me :
A,
Site
80
9C
1 0C
volume
(IVS)
II ; B,
site
IV.
Vo l um e at F i n a l H a r v e s t
The cu b i c vo l ume remo v e d a t
f i n a l h a r v e s t a v e r ag e s about 7 0
p e r c e n t o f t h e t o t al vol ume harve s t e d
from t h e s t and ( t ab l e 7 ) ; t h e r ema i n ­
d e r i s harv e s t e d i n t h i n n i n gs .
Th e
p ro po r t ion o f vo l ume at f i n a l h a r v e s t
var i e s somewh a t w i t h t imespan a n d
growt h r a t e a n d w i t h t h e me asure
of m e r c h an t ab l e v o l ume .
Th us , it
is a l i t t l e gr e at e r on poor s i t es
t h an on good s i t e s a n d is g r e a t e r
i n t e rms o f bo a r d - f o o t vo l ume t han
in t e rms o f t o t a l cub i c - f o o t vo l um e .
( I f b e l o w MAX I MUM , vo l ume at f i n al
h a r v e s t wo u l d b e p r o po rt i o n a t e l y
less . )
The vo l ume a v a i l ab l e a t f in a l
h a r ve s t o f t h i nn e d s t an d s is g e n e r ­
a l l y l e s s t h an t h a t o f c o r r e s po n d i n g
un t h i n n e d s t an d s ( f i gs . 2 6 - 2 8 ,
t ab l e 8 ) .
For s t an d s r e c e i v i n g o n l y
Vo l ume remo ved i n t h i n n i n g s
ave r a g e s a b o u t 30 p e r c e n t o f t h e
t o t a l me r c h an t ab l e cub i c vo l ume
p roduc ed : a l i t t l e mo re on goo d
s i t e s , wh i ch r e q u i r e mor e f r equen t
t h i nn i n g , t h an on p o o r s i t e s .
Propo r t i o n a t e l y l e s s o f t h e t o t a l
produ c t ion o f board f o o t vo l ume
is removed i n t h inn i n gs b e c a u s e
much o f t h e vo l ume in t h i n n i n gs
is in r e l at i ve l y sma l l t r ees w h i c h
con t ribu t e propo r t i o n at e l y mo re
to t o t a l vo l ume t h an to b o a r d - f o o t
vo l ume ,
W i t h our s e l e c t e d r e g imes , t h e
f i r s t comme r c i al t h in n i n g removes
an ave r age of about 1 , 36 0 cub i c
f e e t p e r acre
( 95 m 3 p e r h a ) f rom
s t an d s t h a t w e r e n o t p r e c omme r c i a l l y
t h in n e d and about 1 , 2 1 0 cub i c f e e t
p e r a c r e ( 85 m 3 p e r h a ) f rom t h o s e
t h a t were .
Th e I I - pe r c e n t l ow e r
vo l ume i n p r e c omme r c i a l l y t h i n n e d
s t an ds r e s u l t s f r om t r e e s b e i n g
youn ge r - - and t h us s ho r t e r -- wh en
t h e y re ach the s pe c i f i e d d . b . h .
S imi l ar di f f e r e n c e s b e t we e n s t ands
that we re pre comme r c i a l l y t h i n n e d
an d t h o s e t h a t w e r e n o t p e r s i s t
t h ro u gh out a l l s ub s eq ue n t t h i n n i n g s .
The amo u n t o f vo l ume remo ved t ends
t o i n c r e a s e w i t h e ac h s u c c e s s i ve
t h i n n i n g , at a f a i r l y s lo w rat e
fo r cub i c vo l ume but m o r e r ap i d l y
f o r b o ar d - f o o t vo l ume ( f i gs . 2 7 a n d
28 ) .
25
Tab l e 7- F':"ncZ c::T"'.)est i n :::h irmed stands a n percenr:. ?f' =:nei'l' ;o:a:Z
?l'cduc::ion o spt?a{; :'ed rotatiol1 ages, by site} ;;'l'ea::mer.!.",
e su:t'es of production,' trees 6. 0 i nches Z"'..i
::na' !.la:J>':OUG,
Arr'g2Y' :.n a . o. fl .
Measure o f producti on.1i
S i t e , age , and treatment
CVTS
CV4
IV5
SV6
Percent
S i te I, 85 years :
Commerc i a l th n i ng a l one
Precomerci a 1 thinning +
conmercia 1 thinning
15
13
56
55
66
66
67
67
71
71
74
75
Conmerc i a l thinning a l one
Precormlerc i a 1 thinning +
conmer c i a l thinning
19
16
58
56
66
67
67
68
72
72
76
76
27
21
61
58
68
67
69
68
73
73
76
77
42
29
66
62
72
69
72
70
77
74
81
80
45
57
72
73
77
82
62
69
70
74
78
S i te l l , 90 years :
S i te I I I , 95 years :
Conmer c i a 1 thinning a l one
Precorrmerc i a 1 thinning +
corrrne r c i a l thinning
S i te I V ,
100 years :
Corrmerci a 1 thinning a l one
PrecofTlTler c i a 1 thinning +
corrrne r c i a 1 thinning
S i te 'I, 105 years :
Precorrmercia 1 th i nn i n g
corrme rc i a 1 thinning
+
verage
N
number o f trees; G ;: ba s a l area; CVTS ;: cub i c vo l ume of total stem:
CV4 = e uo i e '(o l ume to a 4 - i nch ( l O-cm) top d . i . b . ; IV5 = International board-foot
vol ume to a 5-i nen ( l 3-em) top, 1/4- inch kerf; SV6 = Scribner board-foot vol ume
to a 6 - i n c h ( l 5-cm) top ( S c r i bn e r vol ume is the fonnula version appl ied to
!6- foot l ogs ) .
CV4 , I V5 , and SV6 exclude vol ume i n the s tump.
11
;:
Tab l e 8--P::r..:z t h(Zr"Jest i n hinned s'tands relative to harvest of !ive ';]'ees
n unthinned stwtds at specified l"otation ages, by site, !:Teatmel1t,
znd Val""': ous measta'es of'
" production; trees 6 . 0 inches and la:l'gel'
in d. D. h.l/
S i te I a g e , and
Measure of producti onY
reatment
S i te 1 , 8 5 yea rs :
Conmerci a 1 thinning a l one
?recolmlerci a 1 th i n n i ng 01cOlTTle
l r c i a l thinning
Precorrmerci a 1 thinning g a i nl!
S i te I I , 90 yea rs :
Og
CV4
I
1V5
SV6
Percent
56
50
122
134
85
89
85
89
85
89
86
90
87
93
83
88
83
90
83
90
84
92
86
94
10
Conmerc i a l thinning a l one
Precomne rcia 1 thinning oj.
corrme rc i a l t h i nni n g
Preconrne r c i a l t h i n n i n g ga i n
60
50
Conme rc i a l t h i n n i n g a l one
?recornne rcia 1 t h i n n i n g 040cornne r c i a l thinning
Precornne r c i a 1 thinning 9a i n
64
50
Conmerci a l t h i n n i n g . l one
Precorrmerci a 1 thinning -+corrmerc i a 1 thinning
Precornne rc i a 1 thinning ga i n
74
51
S i te I l l , 9 5 y e a r s :
CVTS
lI8
133
10
12
1 14
132
82
88
16
82
92
82
92
83
96
82
100
12
12
16
22
Si te I V , 1 0 0 years :
105
132
81
89
81
97
81
98
82
105
83
113
26
10
20
21
28
37
130
90
103
105
118
138
S i te V. 105 yea r s :
Preconmerc i a 1 thinning ...
cornne rci a 1 thinning
54
1/ Expressed as percent of v o l ume i n l i ve trees i n a n unthi nned stand o f the same
i n i t i a l s i te i ndex.
S a l vage o f morta l i ty i n unthinned stands would reduce these
. l i t tl e .
-percentages
Y N =
number of tree s ; og = average d . b . h . ; G . basal area ; CVTS = cubic volume
of total s tem; CV4 = cub i c volume to a 4 - i nch ( IO-cm) top d . i . b . ; IV5 = Interna tiona l
board-foot vol ume to a s - i nch ( l 3-cm) top , 1/4- i nch kerf; SV6 = Scribner board-foot
vol ume to a 6 - i nch ( 1 S-em) top (Scribner vol ume is the fonnu l a version a pp l i ed to
16- foot l o g s ) .
CV4 , I V 5 . and SV6 excl ude vol urne i n the stump.
Y P recornne rci a i thinn i ng ga i n i s r ( precoomerc i a l thinning ... conmerc i a l
thi nn i ng) - conmer e i a l thinni ng) t conme rc i a l thinni n g .
26
E ff e cts of Al t e r n at e Thj n n i n g Re g i m es
M i n imum Merchant ab l e D . b . h .
The e f f e ct o f min imum me r ch an t ­
ab l e d . b . h . ( dm ) on t o t a l merchan t ab l e
p r o du c t i o n i s gr e a t e r for st ands
r e c e i v i n g o n l y commerc ial t h i n n i n g
t h an f o r p r e comme r c i a l l y t h i n n e d
s t a n d s ( t ab l e 9 ) b e cause t h e l at t er
were t h i n n e d t o s t an d dens i t i e s
comme n s u r at e w i t h t h i s min imum
d.b.h.
For s t an ds r e c e i v i n g on Z y
c ommer a i a Z t h i nn i n g , merchan t ab l e
y i e l ds wi t h a dm o f 7 . 5 in ch e s
( 1 9 em ) a r e l e s s t h an t h o s e wi t h
a dm o f 6 . 0 i n c h e s ( 1 5 em ) b y a l l
Re l a t ive
meas u r e s o f vo l ume .
r e du c t i o n s i n y i e l d are great e s t
o n s i t e I V and p r o gr e s s ive l y l e s s
w i t h i n cr e as i n g s i t e i n d e x .
Yield
r e duc t i o n s a r e l e s s wh en i n c r e a s i n g
p r o p o r t io n s o f t o t a l vo l ume are
nonmerchant ab l e ; t h u s , l es s for
board- foo t vo l ume t han for cub i c
vo l um e .
F o r pre a ommer c i a Z Z y
t h i nned s t and s , d i f f er e n c e s a s s o c i ­
at e d w i t h dm- - an d , t h us , w i t h
s p a c i n g o f t r e e s - - ar e mino r .
As
Tab l e 9--Effecr; :;j 'ninimwn meraham;ab le ':. CJ . h . (am) o n merchantable yield
to specif ed ro ation ages) Db $: e) trea entJ
uarious
measures of :JoZwne; when am ·is - , S i.nohes Versus 0 . 0 inches
Meas ure o f vol umel!
Treatme n t , s i te , and age
CVTS
CV4
IV5
SV6
ABSOLUTE D I F cc R E NC E
- - Cub i c feet - -
- - Boa rd feet - -
Commerc i a l t h i n n i ng a l one :
S i te I , 85 years
S i te I I , 90 years S i te l I I , 95 years S i te I V , 100 years 994
990
951
879
858
850
813
744
4 , 499
4 , 1 32
3 , 818
3 , 19 5
2 , 958
2 , 450
1 , 98 1
1 , 390
S i te
S i te
S i te
S i te
S i te
299
323
324
305
259
198
220
218
199
155
1I - 19
81
-13
- 1 60
- 29 7
-1 ,416
- 1 , 45 3
- 1 , 56 3
- 1 , 72 4
- 1 , 80 1
Precommerc i a 1 thi nni n g +
corrrn e rc i a 1 t h i nn i ng :
I , 85 years
I I , 90 years I I I , 9 5 years I V , 1 0 0 years . V , 1 0 5 years
PERCENTAGE D I Fc:RENCES
Percent
Commerci a 1
thi nni ng a l one :
S i te I , 85 years
S i te I I , 90 years
S i te I I I , 9 5 years S i te I V , 100 years 4.2 5.1 6.4
8.5
3.7
4.6
5.7
7.6
2.8
3.3
4.3
5.6
S i te
S i te
S i te
S i te
S i te
1.2
1.6
1.9
2.4
3.0
.8
1.1
1.4
1.6
1.9
0
Precommerc i a 1 th i nn i ng +
commerc i a l th i nn i ng :
11
( IO-cm)
( 1 3-cm )
( I S-cm)
l og s ) .
I , 85 years
I I , 90 years
I I I , 9 5 years
I V , 100 years
V , 105 years
.1
0
- . 2
-.7
2.1
2.3
2.7
3.2
-1.0
-1.2
-1.8
-2.8
-5.3
CVTS = cub i c vo l ume o f tota l s te m ; CV4 = c ub i c vo l ume to a 4 - i nch
top d . i . b . ; IVS = I n terna t i ona l board- foot vo l ume to a 5 - i nc h
top , 1 / 4- i nch kerf ; SV6 = Scri bner board-foot vo l ume to a 6 - i nch
top ( Scri bner v o l ume is the form u l a vers i o n a p p l i e d to 1 6-foot
CV4 , IV5 , and SV6 e x c l ude vo l ume in the s tump .
Di fference i s y i e l d when dm (mi n i mum mercha n ta b l e d . b . h . ) = 6 . 0
i nches mi nus yi e l d when d m = 7 . 5 i nches .
Percent i s th i s d i fference
d i v i ded by the forme r .
1I Nega t i ve d i fference means y i e l ds a re greater when dm = 7 . 5 i nc h e s
( i . e . , wi th wi der spac i ng ) .
27
wi t h s t ands rece i v i n g o n l y
comme r c i a l t h i nn i n g , reduc t i o n s
7.5
c ub i c v o l ume y i e l d when dm i s
i n c h e s ( 1 9 cm ) i n s t e a d o f 6 . 0
( 15
site
cm )
increase with
index .
In
t e rms
vo l ume i n mer c han t ab l e t r e e s wh i c h
die prior t o thinn ing . Th i s l o s s
is part l y o f f s e t b y s a l v a g e o f
in
inches
decreas i n g
some o f t h e s e d e a d t r e e s when t h e
f i r s t t h i nn i n g i s made .
An addi­
of
t ional ,
S c r ib n e r
t re e s ;
the
howeve r , p r o du c t i on
t h e s t and w i t h f ew e r
r e l at ive improveme n t
increases with
b ut
may
The
del a y e d
Th i s
Th i n n i n g
maj o r
Tabl e
thinning
is
l o ss
is
the
of a
sma l l ,
is
i l l us t ra t e d
for
a
site
t ab l e
10 .
examp l e ,
gains
i n m e r c h an t ab l e
CVTS due
to
In
comme r c i a l
th is
thinning
10 - - Effeat on usab le production (CVTS) of de laying aOlTTTleraial
thinning in a site II n a t ura l s tand w h e n m i n imum
merahantab le d. b . h . i8 6. 0 inohes
Stand age (yea rs )
Stand and i tem
30
Unthi nned s tand : Cumu l a ted mo rt a l i ty
Cumu l a ted growth
0
0
" Captured" mo r t a I i ty
0
T h i nn d at age
Net ga i n
Adj usted net ga i
Th i nned at age
0
0
!
51
I
- - - - C u b i c feet -
439
3 . 09 3
1 . 534
6 . 82 2
I
67
3 . 032
1 1 . 09 3
90
Percent of
poten t i a l
ga i n
-
4 . 953
1 6 . 088
792
439
193
1 . 534
426
3 . 032
693
4 . 953
1 . 006
3 . 94 7
3 . 155
0
0
n1!
100
39 :
Y 390
Cumu l a ted " ca ptured" morta l i ty
Cumu l a ted " l os t " growth
Net ga i n
Adjusted n e t ga i
Th i nned at age
I
39
30 :
Cumu l ated " c a ptured" mo r ta l i ty Cumu l a ted " l os t " growth
0
1 . 485
317
2 . 983
680
4 . 904
1 . 105
3 . 79 9
3 . 007
nY
95
51:
Cumv l a ted "ca ptured" morta l i ty
Cumu l a ted " l os t " growth
Net ga i n
Adjusted net g a i
890
o
2 . 388
491
4 . 309 1 . 066 3 . 24 3
2 . 451
nY
78
11 Adj us ted net ga i n = d i fference between captured morta l f ty and " l os t " potent i a l
growth mi nus sa l va b l e morta l i ty at fi na l harvest in unthi nned s tands .
Y Assumes that s a l vage at fi r s t commer c i a l th i n n i ng · 80 perce t of tota l
lO-year mercha n ta b l e morta l i !l t diD ra t i o at f i rs t commerc i a l th i nn i n g .
diD i s the
Thus ,
ra t i o o f
o f cut trees to ug of a l l merchantab l e trees present before. thi n n i n g .
diD
1 .0 .9
.8
28
due
progre s s i ve l y l on ge r de l ay
r e s u l t in s ub s t an t i a l l o s s es .
s t an d i n
loss caused by
comme r c i a l
smal l e r ,
i s made .
The net e ffect
s h o r t de l a y may b e q u i t e
d e c r e as i n g s i t e
qual i t y .
De l a ye d F i r s t
but
t o a gre a t e r r e du c t i o n in growth
pe r acre o n ce t h e f i r s t t h i n n i n g
v o l ume ( SV6 ) ,
is g e a t e r in
Percent s a I vab I e
80
89
100
II
- - - ----. .. - . .- . - - - - - . - - - . ---
��------ .------
are 9 5 percen t as gr e at whe n
th i n n i n g i s d e l a y e d 9 y e a r s ( t o
age 3 9 ) as i f it wer e done at t h e
f i r s t poss ib l e a g e ( age 3 0 ) .
If
the f i r s t t h i n n i n g i s d e l a y e d
2 1 y e ars ( t o a g e 5 1 ) , g a i n s a r e
o n l y 7 8 p e r ce n t a s g r e at a s i f i t
w e r e d o n e at a g e 3 0 .
Frequency and S e v e r i t y o f T h i n n i n g
With o u r a s s ump t i o n s , d i f f er e n c e s
in r e s i dual s t o ck i n g l e v e l ( wi t h in
s u g ge s t e d l i mit s ) an d / or f requen cy
of t hinn ing h ave no e f f e c t o n t o t al
cub i c volume p r o duct ion .
Thus , o t he r
r e g im e s a l t er o n l y t h e d i s t r ib ut ion
o f h ar v e s t e d vo lume o v e r t im e and
For
amo n g var ious sizes of t re e s .
the a l t e rnate r e g imes d i s c us s e d
p r e v i o us l y under numb e r an d s iz e o f
t r e e s ( f ig . 2 2A ) , d i f f e r e n c e s i n
t o t a l produ c t ion b y a l l me a s u r e s o f
D i f f er e n c e s
vo l um e are n egl i g ib l e .
i n vo l ume at f i n a l harvest in t h e
s t an d ma i n t a i n e d at t h e l ow · average
stocking l e ve l is 4 t o 7 p e r c e n t
great e r t han in t h e s t an d main t a i n e d
at t h e h i gh average s t o ck i n g l ev e l .
C o r r e s pondin g l y , s t an ds w i t h t h e
great est vo l um e a t t ime o f f in a l
harve s t have a l i t t l e l es s vo l ume
r emo v e d in t h in n i n g s .
Type o f Thi n n i n g
L ikewi s e , t y p e o f t h i n n i n g i s
assumed to h ave no e f f e ct on t o t a l
cub i c vo lume product ion , an d i t h a s
o n l y a s l i ght e f f ect on t o t al p r o ­
duct i o n b y o t h er me asures o f vo l um e .
I f t h e d/D r a t i o p ro gr e s s e s f rom
0 . 9 to 0 . 8 r at h e r t h a n f rom 1 . 0 t o
0 . 8 ( f i g . 2 2B ) , t o t a l p r o du c t i on
by al l me asures o f vo l ume r ema i n s
The amo un t cut
vir t u a l l y t h e s ame .
at each t h i n n i n g i s a l i t t l e l e s s - ­
e s p e c i a l l y a t t h e f ir s t two
t h i n n i n gs - - s o vo l ume rema i n i n g at
f in a l harve s t i s a l i t t l e g r e at e r .
Th i s d i f f e r e n ce in f i n al harves t
vo l ume is , howeve r , l es s t h an
3 p e r c ent .
Extrapolation to Other
Stand Conditions
S t ructure and devel o pment o f
mos t n a t ural s t ands d i f f e r f r om
t h a t o f t h e average n a t u r a l s t an d
wh i c h w e have d e s c r ib e d .
Some s t an d s
a r e u n d e r s t o cked and others o v e r ­
s t o c ke d , r e l a t ive t o t h e aver age .
S ome a r e very uni f orm and o t h e rs
e xt reme l y var i ab l e in compo s i t ion .
I n some s t an ds , the p at t ern o f
h e i gh t growt h r e l a t ive to s t and a g e
i s qui t e d i f f e ren t f rom what we have
as s um e d - - s o s i t e index does not
r emain const ant .
We do not at t emp t
to s p e c i f i c a l l y est imate the e f f e c t s
o f t h e s e var i a t i on s , b u t i n t h i s
s e c t i o n w e b r i e f l y discuss t h e i r
p o s s ib l e e f f e ct s .
U N I F O R M LY U N D E R ST O C K E D STA N D S
A n un d e r s t o cked s t and i s one
i n wh i ch aver age d . b . h . ( D g ) is
sma l l er t h an NORMAL ( f i g . 4 ) for
the numb e r o f trees present .
Th e
d e g r e e o f under s t o cking decreases
as t h e t r e e s grow .
A u n i form Z y
un d e r s t ocked st and has adequat e
crop t r ee s - - t r e e s t hat w i l l re ach
merch a n t ab l e s i z e - -but f ewer e x c e s s
t re e s t h an h as a n aver age s t an d .
Th i s may b e due t o e i ther nume rous
s m a Z Z o p e n i n gs w i t h in the s t and or
a un i formly mis s in g s i ze compon ent
of sma l l ( general l y younger ) t r e e s .
I f , f or examp l e , a s t and has
1 , 0 0 0 t r ee s per acre ( 2 , 4 7 0 per ha )
w i t h we l l - d i st r ib ut e d crop t r e e s ,
it w i l l Zik e Z y develop in a manner
s im i l ar t o that shown in f i gure 2 9 .
The s t a n d w i l l reach MAXI MUM at a
Dg o f about 4 . 3 inches ( 1 0 . 9 cm ) .
At about t h i s t ime , the smal l e r
t r e e s w i l l b ecome supp r e s s e d and
some w i l l die ; t hus , t he st and wi l l
s l owly approach NORMAL through a
comb in a t ion o f growth and mo n : a l i t y .
Wh en t h e s t an d with 1 , 000 t rees p e r
a c r e ( 2 , 4 7 0 p e r h a ) reaches ;\OlAX I MUM ,
t h e l ar gest 4 0 0 t r e e s per acre
( 99 0 per ha ) w i l l have a Dg of abo ut
5 . 1 i n c h e s ( 1 3 . 0 cm ) ; the l at t er
mus t t h en grow to 8 . 0 inch e s
( 2 0 . 3 c m ) at the age o f " f i r s t
po s s ib l e " comme r c i a l t h innin g .
The s e 4 0 0 t r e e s per acre ( 99 0 p e r
h a ) wi l l , have grown w i t h l e s s t h an
average compe t i t i o n dur i n g part o f
t h e i r l i f e and , thus , reach t h i s s iz e at a youn ger age .
By the t im e t h e s t a n d is ready i N' comme r c i a l t h i n n in g , it wi l l f o r a l l pract i c a l
purp o s e s h ave the char ct e r i s t ics
of a f u l l y s t o cked s t an d .
29
300
200
"
"
;:
1l.
:1
w
[
U
"
[
W
Q
"
W
U)
<1
ill
100
80
50
50
40
<i
30
20
2.000 1 .000 800
NUMBER
600
OF
400
TREES
PER
300
200
100
ACRE
Fi gure 29 . --Typical devel opment of a uni forml y
understocked stand .
With our assumpt ions , the
e f f e c t s o f this p a s t under s t o c k i n g
on merchant ab l e y i e l d shoul d b e
r e f l e c t e d en c ir e l y i n t h e age and
s i t e index at t ime o f the f i r s t
commer c i a l t h inn i n g .
Therefor e ,
once t h i s age and s i t e index are
known or e s t imat e d , one can p r e d i c t
f u t u r e de ve l opment o f the m e r c h a n tab Z e
port ion o f the s t an d .
Each year
gained i n age at f i r s t p o s s ib l e com­
mercial t h i nn ing w i l l add about 1 t o
2 percent t o merch an t ab l e vo l ume y i e l d .
The maj o r gain i n age wi l l o ccur
prior t o the t ime t he s t and reaches
MAXI M11M- -wh e n crop t r e e s h ave l e s s
than normal compe t i t ion ; there wi l l
b e a s l i ght add i t ional gain t h e r e af t e r ,
s i n c e t r e e s w i l l be youn ger th an
normal for t h e s i t e .
The gain , r e l a­
30
t i ve t o t h e normal t ime r e q u i re d ,
wi l l de c r e a s e as numb e r of t r e e s
increases .
W i t h 1 , 00 0 t re e s p e r
acre ( 2 , 4 7 0 p e r h a ) , we e x p e c t a
g a i n o f about 6 . 5 p e r c en t .
Thi s
means a gain o f about 1 ye ar o n t h e
b e s t s i t e s an d u p t o about 2 . 5 years
on poorest s i t e s , for s t ands havin g
t h e s ame current s it e i n d e x .
No t a l l uni f o rml y un d e r s t o ck e d
s t an ds wi l l , however , b e h ave in t h i s
I f t r ee s ize is very un i ­
mann e r .
f orm , due t o min imal var iat ion in
f a c t o r s cont r ib u t i n g t o var i at ion
i n s ize--age , genotype , an d
m i c ro s i t e--the s t an d may not t h i n
i t s e l f adequat e l y a f t er r e a c h i n g
MAXI MUM .
I t wi l l then b ecome
o v e r s t o c k e d , w i t h s ub s e quent det r i ­
men t al e f f e c t s o n s t and d e v e l opmen t .
------ -------- - -------"----
O V E R ST O C K E D STA N D S
An o ve r s t o ck e d s t an d i s o n e in
wh i ch Dg i s l arger t h an NORMAL f o r
the number o f t r e e s p r e s e n t .
One
po s s i b l e cause o f t h i s h a s a l r e ady
been not e d .
I f a s t a n d is ve r y
u n i f o rm , t h er e w i l l b e l i t t l e c rown
c l a s s d i f f er e nt i at i o n ; t h u s , f ew
t r e e s w i l l b e l o s t t o mort a l i t y
and most t r e e s wi l l cont inue t o
incre ase i n s i ze-- at a r e du c e d rat e
( f ig . 1 5 ) .
When s u b s t ant i a l mor t a l i t y
f i n a l l y d o e s o c cur in s u c h s t ands , i t
t e n ds to remove f a i r l y l ar g e groups
of t r e e s r at h e r t han s c a t t e r e d
i n d i v i du a l s ; t h i s c r e a t e s l arge
ope n i n gs and r e s u l t s i n a l os s o f
Thus ,
some o f t h e crop t r e e s .
growt h p e r acre is s u b s e q u en t l y
Z e s s than t h a t o f t h e average
na t u r a l s t an d o f the s ame s i t e and
age .
Exces s i ve o v e r s t o c k i n g may
a l s o c aus e a r e du c t ion in h e i gh t
.
growt h .
Gains f rom p r e comme r c i a l
t h i n n i n g in s u c h a s t an d woul d ,
thus , b e g r e a t e r t h an g a i n s f rom
t h i n n i n g an average n a t u r a l s t and
o f the s ame s i t e an d age .
Anot h er po s s i b l e c a u s e o f
overst o c k i n g h a s much l e s s impact
on s ub s equent s t an d d e v e lopment .
Even in s t an ds whe r e s t and s t r u c t u r e
c l o s e l y appr o x imat e s t h a t o f ave r a ge
s t an ds , mor t a l i t y i s e r r at i c i n s t e a d
o f f o l l owin g a smo o t h t r en d as i n
average s t an ds .
Commo n l y , a f ew
years may p a s s in wh i c h t h e r e i s
l i t t l e mort a l i t y ; supp r e s s e d t r e e s
r emain a l i v e ( a l t h o u gh t h e y d o not
grow ) , caus i n g t h e s t an d t o b e come
overst ocke d .
Then a drought o r
other s u c h c l imat i c var i ab l e w i l l
t r i gg e r h e avy mort a l i t y i n o n e
year .
Thi s remo v e s t h e accumul at ion
o f supp r e s s e d t r e e s wh i c h " norma l l y "
might h ave d i e d p r e v i ou s l y and ,
l ik el y , a l s o some wh i ch normal l y
might n o t d i e unt i l l at er .
Th i s
e r r at i c l o s s o f suppr e s s ed t re e s
wi l l , g e n e r a l l y , h ave l i t t l e e f f e c t
on devel opment o f t h e r e s t o f t h e
s t an d .
N O N C O N STA N T S I T E I N D E X
I f h e i gh t growt h d o e s n o t
f o l l ow t h e a v e r a g e pat t ern r e l a t i ve
to s t a n d age , s i t e i n de x wi l l not
b e a const ant .
Thus , i t is not
uncommon f o r s i t e i n d e x t o i n c r e a s e
or d e c r e a s e as t h e s t an d b e comes
o l der .
If s i t e index i s i n c r e a s i n g
( r e l at ive t o our s ) , vo l ume growth
p e r a c r e wi l l b e greater t h an w i t h
a const ant
s i t e i n de x ; if s i t e
in dex i s d e c r e as ing , vo l ume growt h
w i l l b e l es s .
Th e approxima t e
magn i t ude o f t h e e f f e c t c a n b e
e s t im at e d .
F o r e xamp l e , i f s i t e
index i n c r e a s e s f rom 1 70 t o 1 8 0 a s
t h e st and grows f rom ages 3 0 t o 6 0 ,
we e s t ima t e that t o t al cub i c vo l ume
growt h d ur i n g t h i s p e r i o d wi l l be
a.bout 1 3 p e r c ent g r e a t e r t h an i f
s i t e i n d e x r ema i n e d a t 1 70 , a n d
about 5 p e r c e n t g r e a t e r t h an i f i t
h a d always b e e n 1 8 0 .
I R R E G UL A R S TA N D S
O t h e r t h an t h e s e r a t h e r s y s t em­
a t i c d e v iat i o n s f rom the ave r a g e
natural s t a n d , t h e r e a r e i r r e g u l a r i ­
O n e such
t i es i n s t an d compo s i t i on .
irregu l a r i t y i s the p r e s enc e o f
Z arg e open i n gs w i t h i n t h e s t an d
which are nonproduct ive .
Th e r e i s ,
howeve r , a w i de gray ar e a b e t w e e n
th e s e l ar g e o p e n i n g s and t h e sma l l
open i n gs d i s c us s e d p r e v i o us l y .
Trees b o r de r i n g on open i n gs wi l l
grow mo re rap i d l y than i f t h e y we r e
comp l e t e l y s urrounded b y comp e t i t o rs ,
but not eno ugh to o f f s et the m i s s i n g
crop t r e e s .
Each s u c h s i tuat i o n i s
un i que and must b e s o evaluat e d .
Anoth er i r r e gu l a r i t y i s t h e
presence of other species .
All the
f o r e g o i n g a s s umes p u r e Dougl a s - f i r .
I f t h e t r e e s w i t h i n a s t an d i n c l ud e
o t h er s pe c i e s , b o t h y i e l ds an d
re comme nded s p a c i n g o f t re e s m i gh t
b e qui t e d i f f erent .
The e f f ec t s
o f i n c l us io n s o f o t h e r s p e c i e s an d
other i r r e gu l ar i t i es in s t a n d com­
pos it ion are beyond the s c o p e o f
t h i s p ap e r .
Literatu re Cited
Bruce , David , Don a l d J . DeMars , an d
Don a l d L . Reuk ema .
1977 .
Dou g l as - f i r man ag e d y i e l d
s imul a t o r --DF I T - - us er ' s g u i d e .
USDA For . S e r v o Gen . Tech . Rep .
PNW- 5 7 , 2 6 p .
P a c . No r t hwe s t
Fbr . a n d Range Exp . St n . ,
Port l an d , Or e g .
31
McAr d l e , Richard E . W a l t e r H . M e y e r ,
and Dona l d Bruce .
1961 .
The y i e l d o f Doug l as - f i r
in t h e Pac i f i c
orchwe s t .
[ . S . Dep . Agric . Te ch . BUl l .
o . 2 0 1 , 74 p .
Wash i ng t on , D . C .
.
Re inek e , L . H .
1933.
Perfect ing a s t an d- de n s i t y
index for e ven- aged f o r e s t s .
J . Agric . Res . 4 6 : 6 2 7 -6 3 8 .
Reukema , Don a l d L .
1 9 70 .
Fo rty-year deve l opmen t o f
Doug l a s - f i r st ands p l ant e d a t
various spaCings .
USDA For .
Serv o Res . Pap . PNW- I O O , 2 1 p .
Pac . No rthwest :or . and Ran g e
Zxp . St n . , Po r c l and , O re g .
Reukema , Don a l d L .
1 9 72 .
Twen c y-one y e ar deve l o pment
o f Dougl aS- f i r s c ands r e p e a t e d l y
32
t h inned a t vary i n g int erval s .
USDA For . Serv o Res . Pap . PNW- 1 4 l ,
23 p .
Pac . Nor t hWest For . and
Range Exp . St n . , Por t l an d , Or e g .
Reuk ema , D o n a l d L .
1 9 75 .
Guide l in e s for pre com­
merc i a l t h i n n i n g of Dougl as- f i r .
USDA Fo r . Serv o Gen . Tech . Rep .
PNW- 3 0 , 1 0 p .
Pac . NorthWe s t
For . and Range Exp . St n . ,
P o r t l an d , Ore g .
Reukema . D o n a l d L . , an d Leon V .
P i enaar .
1973 .
Y i e l d s with and without
r e p e at e d commer c i a l t h in n ings
i n a h i gh - s i t e - qua l i t y Dougl as ­
USDA For . S e r v o
f ir s t an d .
Res . Pap . PNW- 1 5 5 , 1 5 p . , i l lus .
Pac . Northwest For . and Range
Exp . S t n . , Port l an d , O r e g .
A p pendix
GLO S SARY
Ag e :
tot a l a g e f r o m s e e d .
Ave r age d . b . h . ( D g ) :
D i ame t e r at
b r e a s c he i ght o f t r ee o f average
b a s a l area .
May r e f e r t o e i t h e r
t o t al s t an d or a s p e c i f i e d com­
ponenc of the st an d .
Average n a t u r a l s c a n d ( n atural
s t an d ) :
A stand h av i n g t h e
c h a r a cc e r i s t i c s d e s cribed in t h e
s e c t ion enc i t l e d " n a1: ural s t an ds . "
The s e s t an d s may a l so b e c al l ed
" n o rmal " s 1: ands .
Crop t r ee s ( merch an 1: ab l e compon e n t ) :
Trees wh i c h have at t ained , o r are
e xp e c t e d 1: 0 a t t a i n , a spe c i f i e d
d.b.h.
A curve
Cumu l a t e d- s c and curve :
s howing t h e cumu l a t e d cont r ibu­
t ion o f l ar ge s 1: t r e e s t o t o t al
n umber an d b a s a l a r e a per acre
as s u c ce s s i ve l y sma l l e r t r e e s
are added .
Cub i c vo lume o f t o t a l s t ems ,
CVTS :
i n c l ud i n g S 1: ump and t i p .
CV4 :
Cub i c v o l ume o f s t ems e x c l u­
s i v e o f ( 1 ) t i p above a 4 - i n ch
d . i . b . an d ( 2 ) s t ump be low 1 foot
o r o n e - t e n t h o f t o t al h e ight ,
wh i ch e v e r is l ower .
d(D r at io :
The r a t i o of average
d . b . h . of cut t r e e s c O average
d . b . h . of all mer ch an t a b l e t r e e s
b e f o r e t h i n n in g .
DF I T :
A s t an d s imul ator con s t r u c t e d
t o provide de t ai l e d output r e ­
g ar d i n g man aged- s t an d y i e l d .
Dg :
S e e " av e r age d . b . h . "
( mi n imum merch an t ab l e d . b . h . ) :
The smal l e s t d . b . h . at wh i ch a
t r e e is c o n s i de r e d t o be o f
merchan t ab l e ( mark e t ab l e ) s i z e .
dm
G : B a s a l a r e a per a c r e ; may r e f e r
t o e i th e r t o t al s t an d or spe c i f i e d
c omponent o f t h e s t and .
Gro s s growt h ( growt h p e r a c re ) :
A c t u a l growt h o f a l l t re e s i n c l ud e d
at s t art o f p e r i o d , n o t r e d u c e d
b y mor t a l i t y .
May r e f e r to the
t o t a l s t an d o r t o sp e c i f i ed com­
pon e n t o f t h e s t an d .
Gross p r o d u ct ion ( gr o s s y i e l d ) :
Tot al vo l ume , o r b a s a l a r e a ,
produced by t h e s t an d s in c e i t s
origin , including that l o s t to
May r e f e r
mor t a l i t y o r c ut t i n g .
t o e i t he r t o t a l s t an d o r t o
spe c i f i e d me r ch a n t ab l e compon en t .
Gross y i e l d :
S e e " gro s s p roduc t ion . "
IV5 :
I n t e r n at i o n a l b o a r d - f o o t vo l ume
of st ems e x c l us i ve of ( 1 ) t ip above
5 - i n ch d . i . b . and ( 2 ) s t ump a s f o r
" CV4 " ; 1 ( 4 - i n ch k e r f .
M.a.i. :
Me an ann u a l i n c remen t .
MAXIMUM :
De f in e d b y f i gu r e 5 a n d
cor r e s p o n d i n g t ex t .
( 1 ) Dg , N ,
and G at wh i ch t h e maximum numb e r
o f t r ee s l ar g e r t h an a s pe c i f i e d
d . b . h . i s r e a c h e d i n aver age
nat u r a l s t an d s ; ( 2 ) the approxi ­
mat e max imum s t o ck i n g l e v e l t o
whi ch a given number o f merchant­
ab l e t r e e s s ho u l d b e grown i n a
man a g e d s t an d .
Merch an t ab l e comp o n en t :
t re e s . "
S e e " cr o p
Merchan t ab l e . . . :
P e r t a in s t o mer ­
chan t ab l e comp o n e n t o f s t an d ;
dep e n d e n t on measure o f v o l ume .
Min imum merch an t ab le d . b . h . :
" dm . "
See
N : Numb e r o f t r e e s p e r a c r e ; may
r e f e r to e i t h e r t o t al s t an d o r
spe c i f i e d compon en t o f t h e s t an d .
Natural s t an d :
s t an d .
S e e ave r a g e n a t u r a l
33
Net y i e l d :
Excludes vo l ume l o s t t o
mor c al i t y ; may r e f e r t o e i t h e r
t o t al s t and or s p e c i f i e d merchan t ­
ab l e component .
NORMAL :
D e f i n e d b y f i gure 4 and
corresponding t ex t .
A s t and­
den s i t y i n de x ; D g , N , and G of
t o t al average n at ur a l s t an d .
RECOMMENDED RES I DUAL ( or RECOMMENDED ) :
The min imum s t o c k i n g l ev e l t o whi ch
t h e merchan t ab l e p o r t ion o f a s t an d
wi l l b e reduced a t e ach t h i n n in g .
S i t e index :
Ave r a g e h e i gh t o f domi ­
nant and codom i n an t t re e s at age
1 0 0 , i f h e i gh t g r owth f o l l o ws the
normal p a t t ern .
S ubmer ch an t ab l e t r ee s :
Tre e s wh i ch
are exp e c t e d t o d i e without at t a i n ­
i n g the min imum merchan t a b l e d . b . h .
SV6 :
S c r ibner b o a r d- f oot vo l ume o f
s t ems e x c l u s i v e o f ( 1 ) t ip above
6 - i n ch d . i . b . a n d ( 2 ) s t ump a s f o r
" CV4 . "
VA R I A B LE S A N D R E LATI O NSH I PS E XA M I N E D
P l an t a t i on
P r e comme r c i a l t h inn i n g
Comme r c i a l t h i n n i n g
Cub i c vo l ume grow t h ( 6 V )
Poten t i al 6 V
f ( s i t e , age )
Reduced 6 V w i t h t h i n n i n g
Produc t i on b y t o t a l s t an d
Product ion b y s t an d compone n t s
V
f ( h e i gh t )
Height growt h ( 6H )
Impro ved 6H w j e ar l y s pa c i n g
6
o f t o t a l s c an d
6 D g o f sc an d compone n t s
f ( H ) ; over t im e
Dg
f ( H ) at g i ven t imes
D.b.h.
Dg , N , G of t o t a l s t an d
Dg , N , G o f s t an d component s
Cumul at ed- s t and curve
Mort al i t y , t o t al s t an d
Mor t a l i t y , s t an d compone n t s
S t a gn at i on
=
=
=
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O I SC
DRICE
999-537
I·
I
T h e mission of the P A C I F I C N O R TH W E S T F O R E ST A N D
R A N G E E X P E R I M E NT STATI O N is to provide the knowl.
edge , technol ogy, and a l te rn atives fo r present and futu re
p rotection , m anagem ent, a n d use of fo rest, range , and rel ated
envi ron m e nts .
W i th i n th is o v e r a l l m i s s i o n , the Statio n condu cts a n d
sti m u la tes rese a rch to fac i l i tate and t o accelerate progress
toward the fol l ow i n g goals:
1. P
rov id i n g safe a n d efficient tech n ol ogy for inventory,
protecti o n , and use of resou rces.
2 . Developing and evalu ating alte rnative methods and levels
of resou rce management .
3 . Ach ieving
opti m u m sustai n e d resou rce pro d u ctiv ity
consistent w i th m a i n ta i n i n g a h i gh q u a l ity forest
environme nt.
The area of resea rc h encompasses O rego n, Wash i n gton,
A l aska, and, i n some cases, Californi a, H aw a i i , the Western
States , and the N ation. R es u lts of the resea rch are made
available p romptly . Proj e ct headqu arters a re at:
La Grande, O regon
Portl and, O regon
O l y m p i a , Wash i n gton
Seattle, Washi ngton
W enatche e , W ashi ngton
A nchorage, A l as k a
F a i rbanks, A l as k a
J u neau , A l aska
B e n d , O regon
Corval l i s , Oregon
Mailing address :
Pa cific Northwest Forest and Range
Experiment Station
P. O. Box 3 1 4 1
Portland, Orego n 9 7208
The F O R EST S E R V I CE of the U.S. D e pa rtment of Agricultu re is dedicated
to the principle of multiple use manage m e nt of the N ation's forest resou rces
for sustained yields of wood, 'watei< 'forage'>i.liidlife, and recreation.
Through forestry research;, ' cooperation with ' the States and private forest
owners, and ma nagement of the N ational F orests a nd' N ational G rasslands, it
strives - as d i rected by Congress: - to ' p rovide increasingly greater service to
a growi ng N ation.
; ::
'
"
"
-"
;-�", " ,
The U.S. D e partment oLAgriculture is .an" E q ua l ;Opportunity E m pl oyer.
A p p l i ca nts for all D epartrTlent progra ms ,will be given equal considerati on
without regard to age, race,' col r;,sex, religior ,or" 'national ori g i n .
\
. '" /..I: .i:./>f ::. ·
" ' ----... -