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Light Intensity Related to Stand Density in Mature Stands of,
the Western White Pine Type
C. A. Wellner
Where tolerance of forest trees or subordinatevegetationis a factor in management,the forester
needs a simple field method of Estimating or forecasting light intensities in forest stands. The
following article describesa method developedfor estimating light intensity beneath the canopy
in westernwhite pine forestswhich may have applicationin other types.
compositionclassesbasedon the percentageof
of the westernwhitepine type introduces small-crowned trees in the summation of diamthe needfor a reasonablyreliableyet sim- etdrs or basal area.
ple methodof estimating
light intensitybeneath The relationshipof light intensityto stand
thecanopy.Thisis of'special
importance
where densityis shownin Figures1 and 2. Table 1
partialcuttingsare usedas a meansof ribes was derived from these curves to .aid in detersuppression
in blisterrust controlbecause
suc- miningthe light intensitybeneaththe canopyfor
cessof suppression
depends
uponthe amountof any givenstanddensity.Checksof thesecurves
canopyreserved
in cutting. It is'alsoimportant and the derived values indicate that two out of
in determining
the probablecourseof forestre- three estimates obtained from them will be within
generation
following
cutting;certainlight in- 10 percentof theactuallightintensity.
tensitiesare favorablefor' regenerationof desiredspecies
andotherintensities
are unfavor-ß •Summationof diametersper acre is recom-
HE
use
of
partial
cuttings
inmature
stands
mended as the most suitable measure of stand
able.
densityto use in obtainingan estimateof light
intensity. Basal area summariesgive similar
neaththe canopyis to relateit to measures
of resultsbut require one more arithmeticoperastanddensity.This wasdoneon a numberof tion. Summationof diametersis simplythe addisample
ardas
in mature
uncutandcutover
standstion of diametersat breastheightper acre. This
One methodof estimatinglight intensitybe-
of the westernwhitepine type. Light intensity
measure can be obtained from cruise data if
on thesesampleareaswasmeasured
at midday they containa tally of all stems.
duringthe growing
season
witha Shirleyradiometer
z and standdensitywas obtainedfrom
The principaluseof thismethodof estimating
diametermeasurements
and expressed
in terms light intensityis to determinehow heavya cut
•f summationof diametersat breastheight per
.acre,and basal area per acre.
to make to obtain a desiredlight intensity. To
illustrate,a partialcuttingis to be madein the
The size of the crownsof the various species standgiven in Table 2.
-proved
to beanimportant
factorin theintercep- As the small-crowned
species,white pine and
•tionof light. Hence,the species
weredivided Douglas-fir,make up 73 percentof the total of
'intotwo groups: (1) small-crowned
trees,in- diameters,the averagelight intensityis estimated
.cluding
western
whitepine,western
larch,Doug- from column6 of Table 1.. The equivalentlight
:las-fir,lodgepole
pine,andponderosa
pine,and intensityfor 2,932 inchesof diameterper acre
(2) large-crowned
trees,includi;•ggrand fir, is 25 percent(to the nearest5 percent). If a light
-westernhemlock,westernredcedar,Engelmann intensity of 40-50 percentis neededfor ribes
-spruce,
andalpinefir. Whenthefielddatawere suppression,
2,100-1,650inchesof diameterper
analyzed,
the standswereseparated
into three acre (Table 1) mustbe left after cutting. A trial
•Silvicultu'rist,
NorthernRockyMountainForestand
RahgeExperiment
Station,ForestService,U.S. Department.of Agriculture;Missoula,Mont. Seniormember
S.A.F.
•Shirley,
H. L.' A thermoelectric
radiometer
for eco-
.,logical
useonlandandin water.Ecology
11:61-70.
1930.
16
markingis madein whichall the Douglas-fir,the
larger hemlocks,and poor-vigorwhite pinesare
markedfor cutting,with due attentiongivento
even spacingof treesto be left. This resultsin
a "cut" tally per acre (Table 3).
LIGHT INTENSITYRELATEDTO STANDDENSITY
17
IOO
'•'•'•
ß
-•
•'•-'•
-i80
).-z
STAND
COMPOSITION
CLASSES
CBASED
ON SUMMATION
OF DIAMETERS)
ß
X •
ß
•
68400
PERCENT
SMALL-CROWNED
TREES
•
%
•
o-•3
•
•% •
•%
.,,
SM•CROWNED
•
40
,,
•
•
WES•RN
• •
•
,,
$PEaES
LAR•-C•WN•D
•H
•TERN
DOUGL•FIR
LODGE•
PI•E
•
•CI•
HEMLOCK
•ERN
RE•EDAR
EHGEL•NN
PONDE•SA
P•NE
ALPINE
20
0
1000
2.000
SUMMATION
OF
3 000
DIAMETERS
PER
4000
ACRE
CINCHES)
FIC. [.--l,ight intensitybeneaththe canopyin maturestandsoJ the westernwhite pine.type
relatedto summation
oJ diametersper acre Jot threestandcomposition
classes.
STAND
COMPOSITION
CLASSES
CBASED
ONBASAL
AREA)
ß
80
•8.-I00
I:•I•.•NT
SMALL-CROWNED
TR•E$
'>.Z
1"':3
60
I--•) 40
u
n,
.
ß
E•MALL-CROWNED $PEGIE5
•,• ?
•.$TE•N
WHITE
. NE GRAND
FIR
'• "'••
ß
%
•
•
LARGE-GROWNED
WF..•TERN
LARC" WESTER"
HEMLOCK
DOUGlAS-FIR
WESTERN
REDCEDAR
•
ß
•'•.•
LODGEPOLE
PINE
ENGELMANN
SPRUCE
PONDEROSA
PINE
ALPINE
FIR
20
o.
0
I
I00
BASAL
I
I
200
AREA
300
PER
ACRE
CSQUARE
I
400
FEET)
FIC. 2.--Light intensitybeneaththe canopyin maturestandsof the westernwhitepine type
relatedto basalarea per acre for three standcomposition
classes.
JOURNAL
OF FORESTRY'
18
TABLE
i.--STAND
DENSITY
EQUIVALENTS
FORGIVEN
LIGHT
INTENSITIES
BENEATH
THE
CANOPY IN MATURE STANDSOF THE WESTERN WHITE PINE TYPE
(.From Figures 1 and 2)
Meanlight
intensity•
Overwood
st&nd'
density
as measured
by summation
of diameters
and by
summation
of basalareaperacreforstands
composed
of
beneaththe
0-33percent
34-67percent
68-100percent
canopy
small-crowned trees2
small-crownedtreesa
small-crownedtreesa
(1)
Percent
(2)
(3)
Inches Square/eet
(4)
(5)
Inches Square/eet
(6)
(7)
Inches Square/eet
10
15
20
25
30
35
2500
1850
1600
1450
1300
1150
255
200
160
135
120
105
3700
3000
2450
2100
1850
1650
400
305
245
210
180
160
4000
3450
3100
2800
2550
2300
480 ß
400
340
290
250
215
40
1050
90
1500
140
2100
190
45
950
80
1350
120
1850
:165
50
850
70
1200
105
1650
145
55
60
750
650
60
55
1050
900
90
80
1450
1300
65
70
75
550
450
400
45
35
30
800
700
550
70
55
45
1100
950
800
125
105
90
75
60
80
85
90
95
300
200
150
50
25
20
10
5
450
350
200
100
35
30
20
10
650
500
300
150
50
35
25
15
qn percentof full sunlightat midday during the growingseason.
•Small-crownedtrees with respect to interceptionof light include western white pine, western
latch, Douglas-fir,lodgepolepine, and ponderosapine. Large-crownedspeciesinclude grand fir,
westernhemlock,westernredcedar,Englemannspruce,and alpine fir.
TABLE 2.--STAND TABLE FOR A MATURE UNCUT STAND OF THE WESTERN WHITE PINE TYPE
Summation
D.b.h.
class
White
pine
Inches
Number
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
All classes
2
4
6
8
14
17
18
20
12
8
4
1
1
Number of treesper acre
DouglasWestern
fir
hemlock
Number
1
2
3
1
1
Number
of
diameters per acre
All
White pine and
All
species
Douglas-fir
species
Number
10
12
13
15
12
10
12
15
19
18
11
8
3
2
1
1
1
'19
23
22
23
22
14
9
4
1
1
Inches
i
Inches
20
48
9O
152
180
12
32
60
96
210
304
378
420
286
192
104
28
30
228
322
352
414
440
308
216
104
28
30
2152
2932
LIGHT
INTENSITY
RELATED
TABLE 3.--STAND
TO STAND
TABLE OF TREES TO BE CUT
Summation
D.b.h.
class
lushes
White
pine
Number
19
DENSITY
of
Number of treesper acre
DouglasWestern
fir
hemlock
diametersper acre
All
White pine and
All
species
Douglas-fir
species
Number
Number
14
16
18
20
8
7
8
5
1
2
3
1
22
24
26
28
30
3
2
2
1
1
1
Number
3
2
1
1
1
All classes
Inches
Inches
9
12
13
7
126
144
198
120
126
192
234
140
5
3
2
1
1
88
48
52
28
30
110
72
52
28
30
834
984
The summation of diameters of trees to be
cut is 984 inches. It is estimated that an additional 150 inches of small-diameter hemlock will
quentlyusefulin classifying
residualstandswith
respect
to probablesuccess
or failureof regeneration of desiredspecies.Of course,
thereareother
be destroyedin the loggingoperation. There- methodsfor directlymeasuringlight intensity
fore, 1,798 inchesof diameterwill be reserved,of
that can be ased in such instances.
which 1,318 inchesor 73 percentare white pine
SUMMARY
and Douglas-fir.The light intensitybeneaththis
residualstandis shownby column6 of Table 1
The use of partial cuttingsin maturestands
to averageabout45 percent,which is within the of the westernwhite pine type has introduced
rangeof light intensitiesdesired.
the needof a methodfor estimatinglight intenIf the trial markinghad resultedin a light in- sity beneaththe canopy.A workablemethodof
tensitygreateror lessthan the desiredintensity, estimatinglight intensityis to relateit to measTable I wouldprovidea guidefor increasing
or uresof standdensity.Figuresaregivenbasedon
in a number of
decreasingthe cut to arrive at the desiredin- light intensitydeterminations
uncut and cutover mature stands of the white
tensity.
pine type, relating light intensityto two measSmalltreesin the understoryand cull• often uresof standdensity:(1) summation
of diamk
interceptconsiderable
light. The possibilityof etersper acre,and (2) basalareaper acre.These
manyof thesekindsof treesbeinginadvertently relationshipsare givenfor three standcomposidestroyedin loggingshouldbe taken into ac- tion classes.The figures and a derived table
count. Failure to allow for loss of unmarked
shouldprove a useful guide in decidinghow
treesor to providefor necessary
protectionwill heavyto cut a givenstandin the westernwhite
resultin a higherlight intensitythanplanned. pine type to obtain light intensitiesnecessary
Table I alsoprovidesa meansof estimating for ribes suppression
in blister rust control or
lightintensities
in cutoverstands.Thisis fre- for naturalregeneration
of desiredspecies.