wculturalsystemand 498 bf/ac/yrunder clearcuttingThis 20% reduction
approximates
the long-termreduction
m growth,and thusfutureharvestlevels, that may resultfrom suchan alternative silviculturalsystem.
Reduction in MAI is about 20%, but
the reductionin yield for the first rotation may be somewhat greater.
While standingvolumesat the end of
rotation are comparablefor the two
systems(Table3), thisis primarilydue
to the large volumecontainedin the
overstorytrees(Figure2). If the alternativesystemis continuedbeyondthe
first rotation, some of the overstory
trees and some of the mature
under-
storytrees,will needto be retainedon
site for coarsewoody debrisand second-rotationgreentree reserves.
For our example,PROGNOSISpredictedthat 16 of the original20 overstory trees remainedafter 100 years.
Fourof the originalreservetreeseither
died or were removed
in the commer-
SUMMARY
We believethat the developmentof
alternative silvicultural systems, including those associatedwith "new
forestry"canyield considerable
benefits. Suchsystemscan combinethe in-
herent advantagesof even-agedand
uneven-aged management, e.g.,
greater structural diversity than
strictlyeven-agedstands,andreduced
management complexity compared
with classic
uneven-aged
systems.Silvicultural prescriptions must, of
course,be executedproperly to capture potential benefits and minimize
potential risks. Green tree retention
carries with
it risks and tradeoffs.
For
example, adverse effects related to
windfirmness
and future stand health
maymakethe systemillustratedin our
discussion
inappropriate
in somestands.
The associated
reductionsin growth
and yield are not trivial.Actualreductionsin growth, yield, and value will
dependon suchfactorsas the level of
residual growing stock and species
mix. In our example,currentand first
cialthinning.We assumedthatfour of
the 16 remainingwould be killedand
left standing as snags and future
downedwoody material.Four others,
along with 16 mature understory
trees,were designatedfor "green re-
rotation harvest levels were about one-
tention"
storycompetitionmay furtherreduce
for the next rotation.
There-
third lower than in the clearcutting
system.Smallertree size due to over-
fore, about 13,700 bf/ac was retained
the value of future harvests.
on site,representingnearly33%of the
approximation,our analysissuggests
that this type of alternativesilvicultural systemmay result in a 20% re-
standingvolumeat theendof thefirst
rotation (Table 3).
As a first
Site Index and Height
Growth
Curves
for
Ponderosa Pine, Western
Larch, LodgepolePine, and
Douglas-Fir in
ductionanlong-termgrowth, and thus
future harvestlevels,comparedto traditionaleven-agedsystems.
An importantpoint to emphasizeis
that many of the potentialdisadvan-
tagesof suchalternativesilvicultural
systemsare only negativein relation
to some other system, e.g., clearcutting or single-treeselection.As prioritieschangesodo the objectivesof forest management;when management
objectives
andconstraints
do not allow
eitherclassic
even-agedor uneven-aged
systems,a thoughtfullydesignedand
carefullyexecutedalternativesilvicultural systemmay be a viableoption. []
LITERATURE
CITED
DAmœL,T.W., J.A. HœLMS,A•r• F.S. B•CER. 1979.
Principlesof silviculture.Ed. 2. McGraw-Hill,
New York. 500 p.
F•CLIN, J.F.1989.Towarda new forestry.Am.
For. 95:37-44.
LEa•c, W.B., a•r• J.H. Gorrsacr,•a.
1985. New
approachesto uneven-agedmanagementin
New England.North. J. Appl. For. 2:28-31.
MAttHews, J.D. 1989.Silviculturalsystems.Oxford Science Publications, Clarendon Press,
Oxford, 284 p.
ORtaNS,G.H. 1990."New Forestry"and the OldGrowth
Forests of Northwestern
North
Amer-
ica. A conversationwith Jerry F. Franklin.
Northwest Environ. J. 6:445-461.
SaLWaSS•R,
H. 1990. Gaining perspective:Forestryfor the future. J. For. 88(11):32-38.
SMtTH,D.M. 1986.The practiceof silviculture.
Ed. 8. Wiley, New York. 527 p.
WYCOFF, W.R.,
N.L.
CROOKSTO•, a•r• A.R.
STAG•.1982.User'sguideto the standprognosis model. Gen. Tech. Rep. INT-133. 112 p.
tendency
tounderpredict
heights
atgreater
ages.New siteindexandheightgrowth
curves
arepresented
for eachspecies.
West.J. Appl. For. 7(1):9-14.
Siteindex
anddominant
height
growth curvesare commonlyused to
identify the potential height-growth
patternthat individualsof a givenspeciesmightbe expectedto achievein a
particularplace.This potentialheight
growthcurvemay thenbe usedas the
sitequality"driver" in a yield prediction system.Identificationof the appropriate potential curve is essential
for reliable predictions of future
growthand yield by suchsystems.
Traditionalsitecurve systemssumKelsey S. Milner, School
of Forestry,Universityof Montana,
marize the relationships between
Missoula, Montana, 59812.
height,age (eitherbreastheightor total), andheightat someindexage(SI),
for somespecifiedset of treesbelonging to a defined population. For a
ABSTRACT.Heightgrowthpatterns
from
thatdiffered
significantly
fromthose
in the given species,the summarizationwill
patterns
several
published
sitecurvesytems
forpon- data.Themagnitude
ofthedeviations
often showdifferentheight-growth
derosa
pine(Pinusponderosa),Douglas- variedby levelof siteindex;thisappeared dependingon the populationdefinitions,samplingprocedures,and confir (Pseudotsuga
menziesiivarglauca), to berelatedto differences
in therangeof
western larch (Larix occidentalis) and
sitequalitiessampled.
Thosecurvescon- structionmethodologyused.Any one
lodgepole
pine(Pinuscontortavarlatifostructed
fromstemanalysis
datafromgeolia) werecompared
to stemanalysisdata graphically
similarpopulations
compared 1Fundingandfieldsupportforthisstudy
fromwestern
Montana.Mostof thepub- mostclosely.Curvesconstructed
using were providedby ChampionInternational
lishedcurveshadheightgrowthpatterns guidecurvetechniques
showed
a consistent Corporation,Milltown, MT.
Western
Montana
WJAF7(1)1992 9
of thesefactorscouldcausea parhcular sitecurvesystemto be suboptimal
in estimatingpotentialheight-growth
patternsfor a particularsite.In recog-
wassampledat 31 locations,Douglasfir at 46, western larch at 37, and
derestimated
by a half-year'sgrowth.
The effectof 1 pointin 11 was consid-
ered trivial and no correction
was
lodgepolepine at 39. The meansand
rangesof siteand standcharacteristics made to the data.
nition of this fact, there has been confor the sampleare givenin Table1.
Evaluationof ExistingSiteCurves
Site trees, which were selected in a
tinual regional activity aimed at asFor each species the observed
sessingthe appropriateness
of partic- fashionsimilar to that describedby
ular site curve systemsto a specific Monserud (1984), had the following height:BHagepatternsfor a givensite
indexlevel were comparedwith those
area, and at developingnew curves characteristics:(1) dominant crown
predicted by various published site
where necessary (Monserud 1984,
classin the senseof receivinglight
curve systems.The publishedcurves
from above and from all sides (thus,
VanderPloegand Moore 1989,Means
and Sabin1989).In additionto providtrees growing in openingsin cutover comparedto the data were as follows
ing a closermatchto populations,the
or unevenagedstandswere potential ponderosapine--Tesch 1980, Lynch
1958asadjustedby Brickell1970,Sumnew curvesoften utilize methodology candidates), (2) no substantial top
and data that provide improvedestidamage,(3) healthycrownsof at least merfield1980,and Barrett1978;Dougmatesof potentialheightgrowthpat40% of totalheight,(4) no substantial las-fir--Monserud1984,Cochran1979,
terns.
Summerfield
1980,and VanderPloeg
periodsof suppression,basedon inDue to its ubiquitousdistribution crementcorestaken at breastheight 1989; westernlarch--Schmidt 1976; and
lodgepole
pine--Alexander1967.
andsubstantial
economic
value,Rocky (BH), and (5)potentiallyrepeatable
on
To compareheightgrowth patterns
Mountain Douglas-fir (Pseudotsuga the site. That is, wolf trees or trees
in the data to thosein the published
menziesii
var. glauca)hasreceivedmost
growingon microsites
obviouslydifof the attention in such research in the
ferent from the general conditions curves, a site index had to be obtained
for eachsampletree that was consisInland Empire.Thereis little informa- were avoided.
tionon the appropriateness
of existing
Three trees on roughly a half-acre tent with the variousindexagesused
in thepublishedsitecurves.The study
site curve systemsfor westernlarch area were selected and felled for meadata were appropriatefor the BH-age
surement of "actual" site index (de(Larixoccidentalis),
ponderosapine (Pi50-yrbasecurvesof Monserud(1984),
nus ponderosa),
or lodgepolepine (Pifined to be the total height correCochran (1979), and Summerfield
nuscontorta
var. latifolia).Thepurposes spondingto a ring countof 50 at 4.5
(1980).Forthosecurvesindexedby toof this paper are to compareseveral ft). Becauseof time and moneycontal age, 50-yrbase(Tesch1980,Lynch
sitecurvesystemsfor thesespeciesto
straintsit was assumedthat the pat1958,and Schmidt1976),a compatible
data collected in western Montana,
tern of height-growthfor the tree of
value was estimated from the data via
median site index, of the three felled,
and to provide a new set of height
growthand siteindexcurvesfor each would representthe averagepotential linear interpolation between the
for that location.Thisassumption
ap-
species.
peared reasonableat six sites where
METHODS
stem analysiswas performedon all
three site trees.
Data Collection
The tree of median site index was
Thesedatawere collectedas part of
a generalinvestigation
into sourcesof
variation in dominant tree height
growth patterns (Milner 1987). The
study area was westernMontana, definedastheareaboundedby Missoula
in the south,Libby to the north, the
Montana/Idaho border on the west,
and Helena to the east. Sites were se-
lectedaccordingto levelsof precipitation, temperature, solar insolation,
andthe presenceof suitablesitetrees.
Since values for the stratification variables were not available at the time of
field sampling,slope, aspect,elevation, and geographiclocation were
usedasinitialproxies.Ponderosapine
sectioned at ground level, breast
height,and at intervalsof one-tenthof
treeheightabove4.5 ft, for a totalof 12
sectionsper tree. Annual rings were
countedat the top of eachsection.The
ring count at each sectionwas subtractedfrom that at breastheight to
obtain the BH age of the tree correspondingto the heightof that section
above4.5 ft. Assumingthat, onthe average, sectioncuts (includingthat at
BH) were made at internode mid-
points (see discussionby Dyer and
Bailey1987),the resultingheightdata
are unbiasedwith respectto "true"
BH age (ring count--0.5 yr), for all
pointsexceptthe tip, whichwill be un-
Table1. Meansand rangesof standand sitecharacteristics,
by species,for the westernMontana site index studysites.
Species
Ponderosa
pine
Number
of sites
Site Index (ft)
Elevation (100 ft)
Slope(degrees)
Precipitation(in.)
WJAF 7(1)1992
Lodgepole
pine
31
46
37
39
59
(27-91)
46
(24-66)
71
(50-97)
42
(24-59)
60
(31-86)
48
(20-64)
14
(0-350)
27
(15-50)
10
Western
larch
60
(41-84)
39
(28-57)
(0-32)
Aspect(degrees)
Douglas-fir
20
17
(1-36)
(1-33)
(0-31)
(0-352)
(0-360)
(36-350)
30
(16-55 )
35
(15-60)
14
37
(15-60)
height:totalagepairsbracketingtotal
age50. However,for thosecurvesthat
were total age-base100yr (Alexander
1967),no observationswere available
Therefore,a regressionequationwas
first developedfrom the published
height growth curvesthat converted
heightat totalage50 to heightat total
age 100.This equationwas then used
to convertthe SI base50-totalage observations
in the data to a SI base 100-
total age basis.For thosecurvesthat
were base100-BHage (Barrett1978)a
similarregressionequationwas developed from the publishedcurvesthat
convertedthe SI base50-BH age valuesto SI base100-BHagevalues.Use
of theseconversionequationsmeans
that the published height growth
curves are accessed according to
heightat 50 yearsof age rather than
100.Thus, conclusions
regardingade-
quacyof thepublishedcurvesareonly
relevant to applications consistent
with this modification.
Had observa-
tionsof heightat age 100 been available,differentresultsmighthavebeen
evident. The regression equations
used were:
Alexander(LPP) SI100 =
- 2.99666
+
1.6129 * SI50
Barrett(PP) SI100 =
-2.64174
+
0.6853 * SI50
For each(SI, Age, Height)tripletcontainedin the stemanalysisdata, a predicted height was obtainedfrom the
•20-
.•-5
o
10 20 30 40 50 60 70 80 90
AgeOotal
orbreast
height)
on the site curve). To aid in detection
of age-relatedbiasthe residualswere
grouped by 5-yr age classesand the
means, standard deviations, and standard errors calculated for each class.
The residuals were also examined at
variouslevelsof site index, sinceagerelated trends could vary by level of
site index.
60
80
100 120
-'-Schmid{-WL
+Alexander
]
-•-J/•erud-.DF
+Mo•serud•
+Monserud-SAF
Figure3. Mean heightresidualsfor Douglas-fir height growth curvesby Monserud
(by habitat type series).
appropriatepublishedH = f (SI, Age)
equation. The residual, (observedpredictedheight),wasformedfor each
SI and Age pair and plotted against
age (total or breastheight depending
40
Total
Age
Breast
Height
Age
-mLynch
+Bo'reit
-z-.S•erfield
-•-Tesch
]
Figure 1. Mean height residualsfor ponderosa pine height growth curves by
Lynch,Barrett,Summerfield,and Tesch.
20
lO 20 30 40 50 60 70 80 90
Site Curve
Construction
Siteindex and heightgrowthequations were developedfrom the data
usingproceduresdescribedby Heger
(1968), Dahms (1973), and many others. The proceduresinvolve first fitting simple,linear modelsto the decadal height and site index data and
then predictingthe regressioncoefficientsof theseequationsas functions
of age. Final modelsare obtainedby
substitutingthe latter equationsfor
the appropriate coefficientsin the
former. Though the resulting equations are over-parameterized,
they fit
the dataquitewell andwerejudgedto
Figure4. Mean height residualsfor lodgepole pine and westernlatch height growth
curvesby Alexanderand Schmidt,respectively.
satisfactorily
representthe patternsof
height-growthin the sample.No attempt was made to refine or advance
site curve constructionmethodology
in this study.
RESULTS
ResidualsAnalyses
Figures 1-4 show the mean height
residuals(observed-predicted)
by age
class. Positive
values
indicate
under-
predictions;negative values indicate
overpredictions.The associatedsite
indexcurveswill giveoverestimates
of
site index where the height growth
curve underestimates, and underesti-
Table 2. Site index and heightgrowth equationsfor ponderosapine (PP), Douglas-fir(DF),
westernlarch (WL), and lodgepolepine (LPP).
Site Index Equations:
PP $1 = 59.6 + (4.787 + 0.012544* A - 1.141 * LnA + 11.44/A2) *
(H-4.5 - 121.4 * [1-EXP(-0.01756
* A)] ** 1.483)
DF SI = 57.3 + (7.06 + 0.02275* A - 1.858 * LnA + 5.496/A2) *
(H-4.5 - 114.6 * [1-EXP(-0.01462 * A)] ** 1.179)
WL SI = 69.0 + (-0.8019 + 17.06/A + 0.4268 * LnA - .00009635* A2) *
(H-4.5 - 127.8 * [1-EXP(-0.01655 * A)] ** 1.196)
LP SI = 59.6 + (1.055 - 0.006344* A + 14.82/A - 5.212/A2) *
(H-4.5 - 96.93 * [1-EXP(-0.01955
* A)] ** 1.216)
Height Growth Equations:
o
10 20 30 40 50 60 70 80 90 100
Breast
Height
Age
-•-Cochran
+SL•merfi•l
• VarKler
Ploeg
J
Figure2. Mean height residualsfor Douglas-fir height growth curvesby Cochran,
Summerfield,and Vander Ploeg.
PP H = 4.5 +
+
DF H = 4.5 +
+
WL H = 4.5 +
+
LP H = 4.5 +
+
121.4 * [1-EXP(-0.01756
(1.189 * [1-EXP(-0.05799
114.6 * [1-EXP(-0.01462
(1.703 * [1-EXP(-0.02214
127.8 * [1-EXP(-0.01655
(1.289 * [1-EXP(-0.03211
96.93 * [1-EXP(-0.01955
(1.410 * [1-EXP(-0.02656
* A)] ** 1.483
* A)] ** 2.63) * (SI * A)] ** 1.179
* A)] ** 1.321) * (SI
* A)] ** 1.196
* A)] ** 1.047) * (SI
* A)] ** 1.216
* A)] ** 1.297) * (SI
59.6)
- 57.3)
- 69.0)
- 59.6)
where
SI = site index, breastheightage50 yr base
H = total height
Ln = naturallogarithm
A = breastheightage EXP= exponentialfunction,basee
WJAF7(1)1992 11
Table3. Mean heightresiduals(observed-predicted),
R, and associated
standarderrors,SE,for new heightgrowth
curves.
Species
PP
Age
n
R
10
20
30
40
50
60
70
80
26
29
30
36
31
22
9
4
2.1
0.8
1.1
0.7
0.4
0.7
0.1
1.7
-
-
WL
DF
SE
n
R
SE
n
R
0.41
0.66
0.59
0.43
0.22
0.44
0.75
4.46
51
44
46
35
33
23
14
8
- 0.3
- 0.2
0.1
0.3
- 0.1
0.3
- 0.5
1.1
0.29
0.39
0.44
0.30
0.23
0.49
1.1 6
1.92
31
32
29
29
24
18
14
8
- 0.3
- 0.3
- 0.2
-0.7
0.1
- 0.5
- 0.7
1.4
matesof site index where the height
growthcurvesoverestimate.
Trendsof
residuals
by ageclassfor levelsof site
agreewell with the testdata at young
agesbut there is a cleartrend toward
underpredictionat older ages. This
pattern is stronglypresentat site indexesbelow55 ft but virtuallydisappearsat siteindexesabove60 ft.
The results for Schmidt's (1976)
index are discussed but not shown.
Figure 1 showsthe resultsfor the
ponderosapine heightgrowthcurves
by Tesch(1980),Lynch (1958),Summerfield (1980), and Barrett (1978).
Tesch's,Lynch's,and Barrett'scurves
showsimilartrends:an overprediction
of heightbetween20 and50 yearsand
an underprediction
of heightat older
ages.Thispatternis evidentacrossall
western larch curves and Alexander's
(1967)curvesfor lodgepole
pine(asreindexed for use with these data) are
givenin Figure4. Neithersetof curves
appearsto fit the data particularly
well.
levels of site index but becomes more
Schmidt's
curves underestimate
heightsat ageslessthan40 yearsand
at agesgreaterthan 80. The pattern
pronouncedas site index decreases.
Tesch'sand Lynch'scurvesalsoshow
a tendencyto underpredictheightat
intensifies
as site index increases. Al-
exander'scurvesoverestimateheights
at young ages,but may be adequate
very young ages. Summerfield's
curves fit the data quite well; they
for agesaboveindexage.The pattern
couldbe appliedto the studypopula- of residuals is similar across all levels
tion without incurringany substantial of site index.
bias. The resultsfor the Douglas-fir
sitecurvesby Cochran,Summerfield, Site Curves
andVanderPloegare shownin Figure
2; those for Monserud's curves are
Table 2 gives the site index and
given in Figure 3. Cochran'scurves height-growthequations,developed
from the study data, for ponderosa
and Monserud'scurvesfor the grand
pine, Douglas-fir,westernlarch and
fir habitattype seriesfit the datawell,
but Summerfield's curves and Monselodgepolepine. Graphsof the height
growth equationsare shown in Figrud's curvesfor the Douglas-firand
ures 7-10.
subalpinefir habitat type series, all
As a basisfor assessing
reliabilityof
show various degreesof departure
the new curves, the residuals (obfromthe heightgrowthpatternsin the
data. All three curves tend to underserved-predicted)of SI and height
were obtainedby using the present
predict height for young ages and
stemanalysisdataasinputsto the site
overpredictheightat older ages.This
index and height growth equations.
patternof residualsis mostevidentat
LP
SE
n
R
0.48
0.66
0.65
0.40
0.30
0.49
1.05
1.67
37
33
30
27
22
17
12
10
0.2
0.1
0.4
1.0
0.1
1.5
0.6
2.3
-
-
SE
0.41
0.55
0.67
0.51
0.41
0.45
0.94
1.77
greeof biasin the new equationsmay
be assessedin Tables 3 and 4, which
give the mean residuals,along with
the associated standard errors, for the
site index and height growth equations by age class for each set of
curves.There does not appear to be
any significant
bias.
Figures5 and 6 show the standard
deviationsof the height and SI residuals,respectively,plottedagainstage.
The standard deviation is a measure of
the variationremainingafterthe relationshipsbetweenheight,SI, and age
have been modelled.
This variation
consistsof two orthogonal components (Monserud 1984); within plot
variabilityassociated
with the sample
basedmean;and variabilityof the plot
means about the model. The error due
to the within-plotvariabilitycanbe reducedby increasing
the samplesizeof
sitetreeson a plot. The "plot aboutthe
model"
error cannot be reduced.
It is temptingto usethesestandard
deviations of residuals to calculate the
number of site trees of a given age
needed to obtain estimates of site in-
dex and/or height to some statistical
standard (Monserud 1984). However,
due to the samplingschemeused in
the study (one tree per plot), these
components cannot be separated.
rThus,precisioncurvesare not possible. Moreover, the tree selected was
the one with median
site index from a
low siteindex levels(<60 ft) and tends
to becomelesspronouncedas site in-
Means, standard deviations, and standard errors for the residuals were then
sampleof three.Thus,it is likelythat
the within plot componentof the varianceis seriouslyunderrepresented.
If
dex increases.Vander Ploeg'scurves
calculatedfor 5-yr ageclasses.
The de-
this is the case, then the standard de-
Table4. Mean site index residuals(observed-predicted),
R, and associated
standarderrors,SE,for newsiteindex
curves.
Species
PP
Age
n
R
10
20
30
40
50
60
70
80
26
38
31
36
31
22
9
6
-1.25
1.01
0.54
0.77
-0.36
-0.72
-0.50
-0.47
12 WJAF7(1)1992
DF
SE
n
R
2.28
1.09
0.71
0.50
0.23
0.39
0.69
2.15
46
44
46
31
33
23
14
8
1.90
0.81
0.00
0.17
0.22
-0.90
0.30
-0.78
WL
SE
n
R
1.33
0.92
0.67
0.57
0.27
0.45
0.91
1.40
31
32
24
29
18
18
14
6
1.29
1.05
0.02
0.78
-0.03
0.57
0.21
-0.19
LP
SE
n
R
1.21
1.04
0.87
0.44
0.35
0.46
0.83
1.61
37
33
30
27
22
17
12
10
0.28
-0.68
0.77
1.35
-0.05
-1.36
-0.64
1.31
SE
1.44
1.15
1.04
0.62
0.40
0.41
0.81
1.57
10-
160
150
140
130
160
150
140
130
SI
•
•120
_•,•.-•
..
/ 80
70
•1oo
90
60
50
40
30
20
10
0
10 20 30 40 50 60 70 80 90
Breost
Hei9hl
A9e
lO
1020 30 4050 60 70 80 90100110120
o lO 2o 5o 4o5o 6o 7o 8o 90100110120
viation of residualsapproximatesthe
between-plotvariationonly, and representsthe bestprecisionpossible.Indeed, the plots in Figures5 and 6 resemblethosepresentedby Monserud
(1984)for his Douglas-fircurves,both
m shapeandmagnitude,forlarge(n >
10) within-plot samplesizes.Assuming similaramountsof variability,approximately10 treesper sitewouldbe
requiredto achievethe levelsof preci-
•iguze 9. Ne• hei•t
fled in the samplingdesign.Depending on the underlyingdistributionof
tree heights and ages, greater samplingintensityon a fixedareacansubstantiallyreducethe estimateof SI. For
the presentsitecurves,plot sizeis not
specified,and considerableresponsibility is placedwith the userto select
individualtreesthat (1) exhibitheight
growth patternsat or near the potential for the site,and (2) are potentially
repeatableacrossthe site. If care is
takento ensurethat all sitetreesfully
meet the criteria specified,a larger
tray the height growth patternscontainedin the studydata. Theseresults
were not unexpected;they reflectthe
differences in populations, definitions,samplingprocedures,
andcurve
constructionmethodologiesused by
sion indicated.
number of trees would be taken on a
Of course,it is alsotrue that by increasingthe within-site sample size
one may be significantlychangingthe
populationof site trees used to estimate siteindex, relativeto that speci-
largerarea, the samplingintensityrelative to the underlying distribution
would remain constant, and no bias
would result.
DISCUSSION
With a few exceptions,the publishedcurvesdid not accuratelypor-
12
gzow• •e•
the various authors, relative to the
sampleto which they were compared.
Generally, the results agree with
Monserud's(1985)conclusions
regarding similarityin shapeof Douglas-fir
siteindexand heightgrowthcurvesin
the Pacific Northwest.
Curves
con-
structed from stem analysis based
methodologies
applied to data from
populationsreasonablycloseto the
study area agreedmost closelywith
the test data. These included
Monse-
rud's and Cochran's Douglas-fir
curvesand Summerfield'sponderosa
pine curves. Site curves that utilized
cross-sectional
data and guide curve
techniques(Tesch1980, Lynch 1958,
160
150
140
130
•120
160
150
140
130
•,120
';
Breost
Hei9ht
A9e
Figure 7. New height growth curves for
ponderosapine.
-•-ponderosa
+Douglas-fir
-xbch-•lodgepole
curvesø
/',/•'"'•'"•'
"•60
30
Breast
Height
Age
Figure S. Standarddevition of height residuals vs. age for new height growth
90
•'110
•'100
• 9o
E 90
8o
7O
6o
5o
60
o 50
o
•
40
4o
20
10
0
50
2O
10
0
0 10 20 30 40 50 60 70 80 90100110120
10 20 ,50 40 50 60 70 80 9O
Breast
Height
Age
--•ponderosa
+•glas-fir
--xlatch
-•-Iodge•
Figure6. Standarddeviation of site index
residualsvs.agefor new siteindexcurves.
0 10 20 50 40 50 60 70 80 90100110120
Breast
Height
Age
Figure 8. New height growth curves for
Douglas-fir.
Bredst
Hei9ht
A9e
Figure 10. New height growth curvesfor
lodgepolepine.
WJAF 7(1)1992 13
Schmxdt 1976), on the other hand,
change For the Summerfieldand Bar-
showed
rett curves, it is unclear to what extent
a distinct and consistent un-
derestimationof height at older ages,
suggestingthat the assumption of
equalsitequalityrepresentationacross
all levels of age was not met. Alexander'scurvesforlodgepolepinewere
derived from a sample that encompassed the Rocky Mountain, Inter-
the causesof the differencesare primarily genetic, methodological or
samplebasedin origin.
The new sitecurvesprovidean unbiased summarization
of the relation-
shipsbetween"true" age (as distinct
from ring count) at BH, total tree
mountain, and Pacific Northwest reheightcorresponding
to that age, and
gions. It is not surprising that their
SI (totalheightat a BH ring countof
comparisonto a small, geographically 50). This configurationis mostapproand geneticallycompactpopulation
priate for simulation models, which
should show differences. It was also
use true age (trees are assumed to
notedthat the patternof over and unreach4.5 ft at the end of a growing
derpredictions
in heightrelativeto the
season).Sincering countat BH overstudy data was completelyconsistent estimatestrue BH age by a half year,
field estimates of SI will be biased
with the age-relatedpattern of predictedsite index noted by Alexander downward slightlyunless0.5 is subin the presentationof his final curves.
tractedfromtheringcountpriorto usThus, the differencesmight be both
ing the siteindexequation.It is intermethodological
and geneticin nature.
estingto notethatweretheraw height
Stem analysisbased curves from
data adjustedto the ring count data
reasonablyclose geographicregions (by adding a half years growth), the
bias in field estimation of SI would disdid not alwayscorrespondwell with
the test data. The study area for
appear;only to reappearas an overesVander Ploeg'sDouglas-fircurvesfor
timationof heightfor the true agesaswestern Montana
had considerable
sumedin modelapplications.
overlap with the current study area
The sitecurvesystemdevelopedin
and yet substantialunderestimates
of
this studyprovidesthe user with the
heightwerenotedat olderages.Also,
means to identify potential height
Barrett'sponderosapine curvesand
growth patternsfor ponderosapine,
Summerfield's Douglas-fir curves,
Douglas-fir,westernlarch,and lodgeboth from east of the Cascade crest
pole pine in WesternMontana. Any
(similarto Cochran'sDouglas-firand
polymorphismin curve shape is reSummerfield's ponderosa pine
flectedonly to the extentthat it is associated with levels of site index.
[]
curves), showed different height
growth patterns from those in the
LITERATURE
CITED
study data. The causeof the differences for Vander Ploeg's curves is
ALEXANDER,R.R., D. TACKLE,AND w.G. DAH•4S.
likely relatedto the absenceof plots
1967.Siteindexesfor lodgepolepine,with corwith
site indexes
below
55 ft in his
sample.In the currentstudy, the daa
showa distinctchangein curveshape
at low site indexes;Vander Ploeg's
samplewould not have containedthis
rectionsfor stand density. USDA For. Serv.
Res.Pap. RM-29. 18 p.
BARRETT,
J.W. 1978.Heightgrowthand siteindex
curvesfor managed,even-agedstandsof ponderosapine in the PacificNorthwest.USDA
For. Serv. Res.Pap. PNw-232. 14 p.
Establishmentof Jeffrey
Pine Seedlings from
Animal
Caches
COCHRAN,
P H 1979 Site index and height
growthcurvesfor managed,even-agedstands
of Douglas-fireastof the Cascades
in Oregon
and Washington.USDA For. Serv. Res. Pap
PNW-251.16 p.
DAHI•IS,
W.G. 1973.Grossyieldof centralOregon
lodgepole
pine.Wash.StateUniv., Proc.symp
Managementof lodgepolepine ecosystems.
DYER, M.E., AND R.L. BAILEY. 1987. A test of six
methodsfor estimatingtree heightsfrom stem
analysisdata. For. Sci.33(1):3-13.
HEaER,L. 1968.A methodof constructingsite
indexcurvesfrom stemanalysis.For. Chron
44:11-15.
LYNCH,D.W. 1958. Effectsof stockingon site
measurement
and yieldof second-growth
ponderosapine in the InlandEmpire.USDA For
Serv.Res.Pap.INT-56.36 p.
MEANS,J.E., AND T.E. SAmIN.1989. Height
growthand siteindexcurvesfor Douglas-firin
the SiuslawNationalForest,Oregon.West.J
App1.For. 4(4):136-142.
Mn,NER,K.S. 1987.The developmentof sitespecificheightgrowthcurvesfor four conifersin
westernMontana. Ph.D diss., University of
Montana, Missoula.
MONSER•SD,
R.A. 1984.Height growth and site
index curvesfor inland Douglas-firbasedon
stemanalysis
dataandforesthabitattype.For
Sci. 30:943-965.
MONSER•SD,
R.A. 1985.Comparisonof Douglasfir siteindexand heightgrowthcurvesin the
northwest.Can. J. For. Res. 15(4):673-679.
SCH•4IDT, W.C., R.C. SHEA•R, AND A.L. ROE
1976.Ecologyand silvicultureof westernlarch
forests. USDA For. Serv. Tech. Bul. INT-1520
96 p.
SVM•4ER•IELD,
E.R. 1980a.Siteindexand height
growthof Douglas-firin easternWashington
Oper.Res.Intern.Rep.No. 80-12.Oper.Res
Sec., Div. of Manage. Serv, DNR, State of
Washington.34 p.
SV•4MER•IELD,
E.R. 1980b.Siteindexand height
growthof ponderosa
pinein easternWashington. Oper. Res.Intern. Rep. No. 80-14.Oper
Res. Sect.,Div. of Manage. Serv., DNR, State
of Washington.34 p.
TESCH,S.D., H.R. ZUURING,AND J.L. FAUROT
1980.Ponderosapine sitecurvesfor the BlackfootRiverdrainage,Montana.Res.noteno. 15,
Mont. For. & Cons. Exp. Stn., Schoolof For.,
Univ. of Mont., Missoula, MT.
VANDERPLOEG,J.L., AND J.A. MOORE. 1989
Comparison and development of height
growthand siteindexcurvesfor Douglas-firin
the Inland Northwest. West. J. Appl. For
4(3):85-88.
cienttoaccount
for mostoftheJeffrey
pine
seedlingestablishment
observed.
Cached
seeds
maygainimportant
advantages
over
uncached seeds in the semiarid habitat oc-
cupiedby thispine.
West.J. Appl. For. 7(1):14-20
Food-hoarding
animals
are
known
to
StephenB. Vander Wall, Department
of Biology,University
of
Nevado-Reno,
Reno,Nevada89557.
dispersethe seedsof many plants
These animals cache seeds or nuts un-
der a layer of soil or plant litter, and
the propagulesgerminatein springif
not recovered.
ABSTRACT.
Jeffrey
pine(Pinusjeffreyi)
seeds
havelargewingsandare effectively
dispersed
bywind,but37%oftheseedling
emergence
sitesin spring1989 in theSierraNevadaofwestern
Nevadaconsisted
of
i The author thanks David Charlet, Steve
Jenkins,Hal Klieforth,JosephMcAuliffe,
Don Minore, and Sue Wilson for their assistance.
14 WJAF7(1)1992
Most
attention
has
tight clumpsof seedlings.
By fall 1989, beendirectedtowardcorvids(jaysand
41%ofall emergence
siteswhereseedlings nutcrackers) and rodents that store
survived
hadresulted
fromwhatwereorig- large nuts. Relativelylittle is known
inallyclumps
ofseedlings.
AsJeffrey
pines concerningthe influenceof rodentsas
aged,clumps
became
smaller,andthefredispersersof the seeds of conifers,
quency
ofclumps
decreased.
These
seedling shrubs,and grasses(seePriceandJenclumps
andmanysingleseedlings
emerged kins1986for a review).Amongpines,
fromthescattered
caches
of seed-hoardinginteresthas focusedon the winglessrodents
andcorvids,and theactivities
of
seededspeciesof the softpines(subthese
animalsin thestudyareaweresuffi- genusStrobus),which are dispersed