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CLIMATE:
A FACTOR IN THE ORIGIN OF THE POLE BLIGHT
DISEASE OF PINUS MONTICOLA DOUGL.'
CHARLES
D.
LEAPHART
AND ALBERT
R.
STAGE2
ForestService
ofAgriculture,
U. S. Departmentt
Forest and Range Experiment Station, Ogdent,Utah
IntermouxntainL
Abstract. Measurements of cores or disc samples representingslightly more than 76,000
annual rings from336 western white pine trees were compiled to obtain a set of deviations from
normal growth of healthy trees that would express the response of these trees to variation in
the environmentduring the last 280 years. Their growth was demonstratedto be a function
of temperature and available moisture for the period of climatic record from 1912 to 1958.
Extrapolating the relation of growth to weather to the long tree ring record of western white
pine, we findthat the period 1916-40 representsthe most adverse growth conditionswith regard
to intensityand duration in the last 280 years. This drought, superimposed on sites having
severe moisture-stresscharacteristics,triggered the chain of events which ultimately resulted
in pole blight. If the unfavorable conditions for growth during 1916-40 do not represent a
shift to a new climatic mean and if western white pine is regenerated only on sites with low
moisture-stress characteristics,the probability is high that pole blight will not reoccur for
many centuries in stands regeneratedfrom this date on.
INTRODUCTION
POLE
BLIGHT-ITS
HOST
AND
ENVIRONMENT
profoundly Westernwhitepine is one of the mostdesirable
Climate,in its many ramifications,
influencesthe growthof foresttrees. Likewise, species for managementon approximately312
climateinfluencesthe inceptionand intensificationmillion acres in northern Idaho, northeastern
of tree diseases throughphysiologicalresponsesof Washington, and western Montana (Fig. 1).
for Here it is a seral species in nine habitat types
the treesand theirpathogens. Unfortunately,
many forestedareas few weather records cover (Daubenmireand Daubenmire1968) thatare ocmuch more than the past 50 years; for example, cupied by climax vegetation characterized by
weatherin the westernwhitepine type has been grand fir (Abies grandis (Dougl.) Lindl.), subonly since 1911. How- alpinefir (A. lasiocarpa (Hook.) Nutt.), western
recorded instrumentally
effects
of weatheras recorded redcedar (Thujac plicata Donn), westernhemlock
ever,the integrated
in the growthrings of trees permitus to extend (Tsuga heterophylla(Raf.) Sarg.), and mountain
by several hundredyears our knowledgeof the hemlock(T. mertensiana(Bong.) Sarg.) In the
factors southernpart of thisarea, westernwhitepine fordistributionin time of the environmental
ests occur ratherextensivelyin somewhatbroad
thatinfluenceringwidth.
in the growthrates river valleys and often to the ridgetopson all
Long recordsof fluctuations
of trees have been analyzedchieflyfor archeolog- slopes. Further north to the Canadian border,
ical purposesby dendrochronologists
(Glock 1955, the species is largely restrictedto moist creek
Studhalter1955, Schulman 1956). Shorter se- bottoms,lower benches and flats,and northerly
quencesof growthrateshave providedinsightinto slopes. Pole blighthas occurredonlyto the north
those aspects of climate to which trees respond of the Clearwaterdrainage (Fig. 1).
Pole blightwas firstobservedin 1929. It is re(Fritts 1966, Zahner and Stage 1966). We apstricted
to sites with shallow soils or soils of low
plied bothof thesetypesof analysesto the growth
moisturestorage capacity in the upper
available
historyof westernwhite pine (Pinus monticola
mantleunless these conditionsare mitigated
3-ft
Dougl.) to answerthe following:Do the correlaby some subsurfacesource of moisture(Leaphart
tions of growthwith climateand the historyof
1958). Root deteriorationand rootletmortality
whitepine growthsupportthe hypothesisthatthe
are higherin healthystandson thesesitesthanon
pole blightdisease of westernwhite pine is the
sites where storage capacities exceed 5 inches
resultof an adverselydry climaticepoch? And,
(12.7 cm) in the 3-ft(0.91-m) mantle. Furtherinduced,whatdoes the
ifthedisease is climatically
more,as the trees on the droughtysites develop
historicalrecordtell us of the probabilitythatthe
externalsymptomsof pole blight,the root decline
disease will cause recurrentlosses?
becomes much more prevalent. In severelydis1 Received September 1, 1969; accepted April 14, 1970.
eased trees much of the functionalroot systemis
2 The authors are stationed at the Forestry Sciences
rootlets. Rootletmorof
Laboratory, Moscow, Idaho, maintained in cooperation almostdevoid absorbing
tality is higher in dry than in moist summers.
with the University of Idaho.
CHARLES
230
D. LEAPHART
AND ALBERT
R. STAGE
Ecology, Vol. 52, No. 2
low husummerseasons with scant precipitation,
midity,and a highproportionof clear,warm days
and by winterswithheavysnowfalland fairlylow
temperatures.The existingweatherrecords describeonly the recentclimate-the oldest records
startedin 1911 at the Priest River Experimental
Forest. To extend our knowledgeof climateto
past epochs throughanalysisof growthrings,we
MONTANA
can onlyfocuson thosefactorsof the environment
to whichtree growthrates are sensitive. Such a
studywould most likelymiss the criticalfactors
for a specificpathogen. However, growth-ring
analysis does provideinsightinto past conditions
0~~~~~~~~~~
of moisture stress (Zahner and Stage 1966).
Hence, it shouldalso provideinsightintothe same
aspects of the tree's physiologyaffectedby the
site characteristics
and root decline already associatedwithpole blight.
If we can assume that the climaticvariations
experiencedduringthe last two centuriescan be
of a randomvarirepresentedby the fluctuations
able havinga constantmeanand variance,thenthe
probabilitywithwhichpole blightwill occur in a
particularstand shouldbe the productof the conIT
ditional probabilityfor the site times the probabilitythatat least as severea climaticepoch will
be experiencedduring the criticalperiod in the
lifeof the stand. Leaphart (1958) has estimated
FIG. 1. Location of study plots and the geographic
withwhichpole blightmight
therelativefrequency
distributionof the western white pine type.
occur in pole stands with a componentof this
species. The probabilityincreasedon soils of low
Under stressedconditionswesternwhitepine ap- moisture-storage
capacity and low recharge porootlets tential. However, the surveyfromwhich these
pears unable to keep pace in regenerating
to replacethoselost forany cause fromits absorb- estimateswere obtainedsampledonlyone pointin
ing system. Crown decline is probablya secon- time. Correspondingprobabilitiesof occurrence
daryreactionfollowingdeclineof the root system. should be much lower followingclimaticperiods
Concurrentresearchon the disease in BritishCo- when criticalmoisturestress would prevail only
lumbiahas supportedtheseconclusions(Welling- on soils of exceptionallylow moisture-storage
ton 1954, Molnar and McMinn 1958, McMinn capacity.Our limitedknowledgeoftheconditional
and Molnar 1959, McMinn 1965). For further probabilitydistribution
withrespectto site condidetail supportingthese conclusions,the reader is tions precludesa completemanagementanalysis.
referredto the following:Pole Blight Committee However,studyof the timeseries of variationsin
1952, McMinn 1956, Foster 1957, Leaphart 1957, ringwidthsshouldprovidethe approximateprobLeaphart and Copeland 1957, Graham 1958a, ability distributionof climatic fluctuationsto
1958b,and Leaphartand Wicker 1966.
answerthe questionswe have posed.
Aside fromthe impactof pole blight (Graham
OF DATA
COLLECTION
ofwesternwhitepine
1958b), currentmanagement
has also been severelycurtailedby an introduced Westernwhitepine was selectedfor this analrust disease caused by Cronartiumribicola J. C. ysis forseveralreasons.We were primarilyinterFisch. ex Rabenh. (Ketcham,Wellner,and Evans estedin the fluctuations
of thosegrowthconditions
1968). By itself,this resultingshiftin emphasis that affectthis species even thoughit is not ideal
to managementof otherspecies, or eventuallyof fordendroclimatological
analysisper se. Furtherspecies mixtures including western white pine, more, a comparisonof the growth patternsof
would undoubtedlylessen the futureimpact of healthytrees and diseased trees of the same age
pole blight.
mightprovideinsightsupplementalto Marshall's
The climateof the nine habitattypesin which (1927) into conditionsantecedentto the developcorwesternwhitepine occursis characterized
by short mentof pole blight. Even if growth-climate
OMOSCW
GEOGRAPHIC
EUDISTRIBUTION
o
STUDY
PLOTS
WEATHER
STATIONS
1
2
M2ILES
EarlySpring1971
CLIMATE AND POLE BLIGHT DISEASE
231
treatment accuratereadingsof each annual ring. A sliding
relationswere not strong,mensurational
stage device under X45 magnification
betweenthe growthpat- micrometer
mightshow differences
ternduringthe first50 years of growthin several was used to measure width to the nearest onecategories:old stands,young healthystands,and hundredthof a millimeter. Slightlymore than
76,000 annual rings were recorded,nearlyall of
young stands currentlyaffectedby the disease.
One plot was establishedin each of 23 stands whichwere used in one or moreanalyses.
The two cores or strips fromeach tree were
(Fig. 1). Most plots were in the vicinityof the
Priest River ExperimentalForest on the Kaniksu cross-datedto assure correctannual measurements
National Forest and the AveryRanger Stationon fromthe year 1958 to the age of the tree at the
the St. Joe National Forest because the longest pith. Trees within each plot were then crossweather records in the westernwhite pine type dated so that for any year withinthe age reprewere availableat thesetwo locations. In addition, sented by the plot an accurate average annual
two plots in standsbetween50 and 100 years old growthfor each tree in a plot would be obtained.
were selected near Pierce, Idaho, on the Clearwater National Forest.
ANALYSIS
OF CORE AND WEATHER
The 23 plots were selectedfromstandsgrouped
MEASUREMENTS
intofourbroadage classes: 50-100, 100-150, 150Normal growthvs. age curves
200, and 250-400 years. Except forfiveplots in
Our objectiveforthe compilationof the annual
the older age groups,all stands were uniformin
age; thatis, the age spread in a plot was less than ring data was to obtain a set of deviationsfrom
20 years (Table 1). Althoughthe age spans of normalgrowthof healthytreesthatwould express
plots 2, 6, 10, 13, and 21 were greaterthan 20 theresponseof thetreesto the environment.The
years,these stands had an even-agedappearance. formof growthexpressionhad to be such thatthe
The oldest stand, in which only two trees (379 deviationsfrom it would show relativelygreat
and 384 years) were sampled,was located in an variationbetweenyears and low variationamong
uneven-sizedstand that had a historyof at least treeswithinyears. In addition,the deviationhad
two burns,the last of whichoccurredabout 1890. to have constantvariancewithrespectto tree size
Plots were selectedto representstandsof aver- and age.
Duff and Nolan (1953) found that data from
age density. Nearly all were locatedon soils with
good internaldrainageand on moderateto steep widthsof annual ringstaken in verticalsequence
slopes. Severe exposures were avoided, except (a constant number of rings from pith) were
forone plotin the250- to 400-yearage class. Most superiorto those fromwidthstaken in horizontal
environmental
effects
of the more accessibleand suitablestands of that sequence for demonstrating
age class had been harvestedor partiallycut in on growth. However, the physical job of sampling the verticalsequence precluded its use on
past years.
large trees.
all
white
trees
the
336
western
sampled
pine
Of
were dominantwith respect to their immediate Basal area incrementhas long been recognized
neighbors. Except for 52 trees in four plots in as a measureof growththatis fairlyconstantover
the 50- to 100-yearage class, all were healthyand a considerableperiod in the lifeof a tree growing
of good vigor. The 52 trees were diseased with under uniformconditions. However, basal area
varies widelybetweentreesin the same
pole blight and were used in analyses separate increment
stand. The largertrees with bettercrowns and
analyses.
fromthe climate-growth-correlation
fasterthando their
Two cores, approximately4.5 mm in diameter, rootsystemsgrow consistently
were takento the pithwithan incrementborerat less favorablysituatedneighbors. Relative basal
4.5 ft (1.37 m) above mean groundlevel. Cores area growthrate (basal area incrementdivided
were taken on the opposite sides of nonleaning by basal area) is less sensitiveto this source of
trees; on leaning trees they were taken at right variation.
Both basal area incrementand relative basal
anglesto each otherfromthetwo quadrantsopposite the zone of greatestcompression. Abnormal area incrementchange with increasingtree age.
depressionsor swellingswere avoided when se- To removethis trendwith age all the data from
curingcore samples. In four of the older plots, healthyplots were averagedby age. The two age
sample trees were felled and a section at 4.5 ft sequences of average growthrates thus obtained
(1.37 m) was removed. Two radial stripsfrom will be referredto as the normalgrowthtrendfor
the bark to the pithwere cut at rightangles from the logarithmof relativebasal area increment(in
this section; each representedthe average radius R) and basal area increment(BAI), respectively.
of plots in several age classes
The distribution
insofaras possible.
Cores were air-driedand smoothedto facilitate was such that certaindates tend to clusterabout
232
CHARLES
D. LEAPHART
50-100 years
Plot
Number
of
AND ALBERT
100-170 years
Age
Plot
R. STAGE
Ecology, Vol. 52, No. 2
1. Distribution of plots by age class
TABLE
170-250 years
Number
of
Age
Plot
Number
of
250+ years
Age
Plot
Number
of
Age
number
trees
range
number
trees
range
number
trees
range
number
trees
range
19
16
08
07
05
20
17
03
15
04
15
23
15
27a
15
34b
308
15
12
11
21d
15
12
10
50-58
57-64
58-64
58-64
58-68
59-64
60-63
60-67
60-81
61-67
74-83
83-92
14
02
09
11
10
8
15
10
114-128
116-134
118-125
124-141
02
01
10
5
10
15
152-167
179-194
183-211
06
13
12
21
22
14
10
10
10
2
264-295
254-296
269-278
270-303
380-384
Total
217
43
30
46
aIncludes 12 diseased trees.
bjneludes 14 diseased trees.
ajneludes 15 diseased trees.
djncludes 11 diseased trees.
dard deviationsabout the means for several portionsof thecurve.
Deviationsfromnormalgrowth
Differencesbetweenthe measuredannual increnormalgrowthcurve
mentsand thecorresponding
each
accordingto the age
tree
for
computed
were
VW~i.
lTT
TF
lT
fllll lII
-llll
l l~r~
flF
of the trees when the incrementwas formed.
These deviationswere averaged withinyears for
trees in all healthyplots. In this analysis,283
trees with a total of 34,728 annual rings were
-6.
represented. Comparisonof these deviationsfor
two expressionsof growthshowed that the ratio
of variancebetweenyearsto variancewithinyears
AGE
was 123.0:1 for in R and 1.72:1 for BAI. The
FIG. 2. Normal trend of adjusted in R with tree age.
of the formermeasure for studying
advantage
Vertical bars show standard deviation.
growthresponseis obvious. Hereafter,all growth
certainages. If these particulardates are char- analyses used deviationsof the logarithmof relacterizedby abnormalgrowthrates, the normal ative basal area increment.
growthtrendswould be warpedat the correspond- A curve of the form:
1nR
a + b1n (age) + c [in (age) ]2
ing ages. To overcomethis possibility,a second
set of adjusted normal growthtrends was pre- was fittedto the sequence of averages for ages
pared. The treeswere dividedinto 14 age classes, greaterthan10 years. Each averagewas weighted
withdivisionpointsas near as possibleto discon- in the least-squares solution by the number of
tinuitiesin the age-class distribution. For each ringsin the average; hence,the weightingwas inoftheseage classes,a scalingfactorwas calculated versely proportionalto the variance. Although
in such a mannerthat the productof the scaling the data were predominantly
linear,the coefficient
factortimes the average-growth rate would be forthe square of the logarithmof age was signifiequal forall age classes (as of 1958) forthe years cant at the 1/10% level.
correspondingto 36-50 years of age. The adThe deviations from this smoothed normal
justed average growthrate for each year of age growth curve of individual annual rings from
was then computedas the mean over all trees of healthytrees greaterthan 10 years of age were
the growthrate times the scaling factorappro- collatedby age and theiraveragescalculated. The
priate to each tree (Fig. 2). This adjustment historyof theseaverage deviationsfor all healthy
processreducedthe large departurefromlinearity trees is shown in Fig. 3A for the period from
in the data at an age of about 70 years. Vertical 1680 to 1958. Slow growthis indicatedin this
bars in Fig. 2 indicateaverage values of the stan- historicalsequence by negative deviations. Al-3.
-
1
-5.
710
20
40
60
80
e00
200
30
400
A
A
,n
,ir
1680
1700
I
yuC
I
B
233
CLIMATE AND POLE BLIGHT DISEASE
EarlySpring1971
nn
1720
1740
I
I .
~a
L-
'
1780
1760
I
UDQ
n ,Lnfl
nniMr-Nl
h l<
n,
n"nUniA
4,
,
1R
lnUdu
I
1800
g
I
1820
1840
I
U -UU~ W0
1900
1920
-L~uQu U]09'UjulUr
4|~0
1860
1880
I
I
~
Ii'1
1940
1960
W
FIG. 3. (A) Average deviationsfromthe adjustednormalrelativegrowthtrendsortedby date. Periods
above the solid line correspondto periodsof betterthan average growth. (B) Sequence of deviationsafter
removingeffectof serial correlation.Verticalscale has been expandedto achievea standarddeviationequal
to the A series.
though records of the oldest trees in the study
startedin 1574, at least 10 trees older than 10
years of age at breast heightwere deemednecessaryto obtaina stableaverage; hence,1680 is the
earliestdate in thissequence.
The sequence of negative departures,beginning about 1916 and continuingto the end of the
record, clearly representsthe most unfavorable
growthforwesternwhitepine in the 280-yearsequence. The decline beginningin 1905 also is
evidentin Marshall's (1927) data. Conversely,
theperiodsfrom1853 to 1882 and 1900 to 1908when many of our blightedstands germinatedwere characterizedby unusuallyconsistent,rapid
growthrates.
of thissequence
The serialcorrelationcoefficient
is +0.81. With a lag of 15 years,the serial correlationcoefficient
of +0.3 is stillfairlyhigh.
Climaticconnections
Regionalweathersummaries.-Weatherrecords
fromthe three stationsused in this studyin the
western white pine type indicate similarityin
forthe
deviationsfrommean annual precipitation
water year (October 1 throughSeptember30)
(Fig. 4). Average daily mean and maximum
temperaturecurves for the months of April
throughAugust also indicatea generallyuniform
climaticpatternwithinthe timbertype. Nonpole
blight areas (Pierce station) annually receive
than do most pole blight
muchmoreprecipitation
areas typifiedby Priest River and Avery. From
1916 to 1940,a periodof criticalstressforgrowth
at PriestRiverwas
(Fig. 3A), annualprecipitation
below the46-yearmean of thethreestations(Fig.
4) in all but three of the 24 years, whereas at
30 -
20 -
10 -
,0L
Pierce
-10V
20 -
10 0
l
0
Avery
-10 -
-20
F
-
10
-10
Priest River
1915
1920
1925
1930
1935
1940
YEAR
1945
1950
1955
1960
FIG. 4. Deviations from mean annual precipitationfor
three weather stations. Year extends from October 1 to
September 30. Zero ordinate of each panel corresponds
to the grand mean of the three stations (34.15 inches/year
(86.78 cm/year)).
Pierce it droppedbelow the mean in only six of
them; threewere consecutive,1929-31.
Precipitationwas higherduringthe water year
and also higherduringthe growingseason (April
throughSeptember)at the Pierce station. Pierce
averages about 2.5 and 3.4 inches (6.35 and 8.64
cm) higherthan Avery and Priest River, respectively,duringthe growingperiod. More favorable conditionsfor tree growthoutside the pole
CHARLES
234
D. LEAPHART
AND ALBERT
R. STAGE
Ecology, Vol. 52, No. 2
cause theyare thelongestavailableforthewestern
whitepine type. Data fromsix oftheplotsclosest
to the Priest River Experimental Forest were
compiled for the years 1912-58. The climatic
factorsconsideredon a daily basis were temperand moisturestress.
ature,precipitation,
Daily values of mean temperatureand precipitation,as measuredat the Priest River ExperiFIG. 5. Deviations, from monthly mean daily precipidegree
tation for the years 1922-60 at the three weather stations mentalForest,were approximatedby fifth
(monthly means in parentheses). The higher level of orthogonalpolynomialsfor the period April 1 to
annual precipitationat Pierce extends well into the grow- October 24. In addition,an estimateof evapoing season.
was obtainedby means of a day-bytranspiration
programthatused soil-moisture
day water-balance
storageand depletioncurves specificto each plot.
The differencebetweenThornthwaite'spotential
and the estimatedevapotranevapotranspiration
spiration,which we have called moisturestress
(Zahner and Stage 1966), was included in the
of the orthoanalysis in termsof the coefficients
gonal polynomials.
The dependentvariablein this regressionanalbetweenthe
ysis was the average of the difference
April
logarithmof relativebasal area increment(annual
FIG. 6. Deviation from monthly mean daily temperarea) for the trees in
basal area increment/basal
ature for the years 1922-60 at the three weather stations
trend with age.
the
corresponding
and
one
plot
(monthly means in parentheses). Priest River Experiment Station is warmer in the spring than Pierce; tem- From the six plots with46 years of records,276
peratures are higher throughoutat Avery.
observationswere obtained upon which to base
the regression.
blightareas are also shownby the deviationsfrom
Climaticvariablesfor both currentand precedthe monthlymeansof thethreestationsfrom1922 ing seasons and the dependentvariable for the
through1960 for average daily precipitationand precedingseason were included as independent
mean temperatures(Fig. 5 and 6). The mean variables,along with linear and quadratic timedaily temperaturesare significantlylower and trendvariablesthatwere unique to each plot. In
daily precipitationhigher throughJune for the all, therewere 49 variablesin the regression. For
system,the
Pierce station than for the other two stations. this mixed autoregressive-regressive
The stationsdifferlittlein Julyand August,but usual least-squaressolutionhas been shownto be
by SeptemberPierce again exhibitsa more moist the best unbiased linear estimatingprocedure
environment. The high temperatureregimesat (Durbin 1960).
The completemodel accountedfor 78% of the
Avery predominatethroughoutthe season.
Correlationof growthwith zveather.-A corre- variancein the deviationsfromnormalbasal area
lation between fluctuationsin tree growthrates growth. Moisture stress,temperature,and preand changesin weatherhas been almostaxiomatic cipitationtogetheraccountedfor56% of the variin ecology and forestry. However, to define ance remainingafterthe effectof the lagged deweather and growth rate so as to demonstrate pendentvariable was removed. Moisture stress,
capacity
that such a correlationexists has not which depends on the moisture-storage
statistically
always been easy. Hence, a carefulanalysis of of the soil and the seasonal patternsof precipitaaccounted for 28%
the relationof ring width of westernwhite pine tion and evapotranspiration,
base of thevarianceremainingafterdirecttemperature
to climaticfactorswas a necessaryinferential
effectswere removed.
to attributethe historyof growthfluctuationto and precipitation
to supThe variationaccountedforis sufficient
climatic variation. Zahner and Stage (1l966)
describein detail the conclusionsbased upon the portthe hypothesisthatthe sequenceof deviations
analysisof the data used in this study. However, fromnormal relativebasal area growthsubstana briefsummaryis appropriatehereto supportthe tially reflectsthe sequence of climaticfactorsafhypothesisthatclimateis a factorin the originof fectingwesternwhitepine growth. In particular,
moisturestress is one of the more importantasthe pole blightdisease.
The weatherrecords at the Priest River Ex- pects of climateto which westernwhite pine reperimentalForest were used for this analysisbe- sponds. However,no one aspect of climatetaken
-.012 -
_
_
Apoa
(any
(44.0)
_
Mw
(.061
May
(52.9)
_
_
June
.089)
June
(03.9)
_
_
July
1.029X
July
(85.9)
August
t.031)
August
(64.0)
September
t.069)
September
(506.4)
Early Spring 1971
CLIMATE
AND POLE BLIGHT
235
DISEASE
to explain variations in tree outside pole blightareas, i.e., stands withinthe
alone is sufficient
growth. Considerationof day-by-dayvariations Clearwaterdrainageor in areas physiographically
in climaticfactorsis also required.
or geologicallydifferent
and separated fromthe
An additionalimportantaspect of this regres- diseasedand theiradjacenthealthystands,differed
fromthe above age-class trend and
sion analysiswas theestimateoftheautoregression significantly
coefficient.The coefficient
representsthe serial fromthe average for other healthytrees in the
correlationwitha lag of 1 yearbetweensuccessive class (Table 3). However,even thesetreesshow
deviations from normal growth. Because it is a consistently
decliningtrendthroughthe 5 decestimatedin a multipleregressionincludingthe ades. Thus, even though the climate of these
precedingyear's weather,it does not includethe stands representedby Pierce is more favorable
effectof persistencein weatherthat may occur for tree growththan the climateof diseased and
fromyear to year. Thus, the value for the auto- adjacent healthystands representedby the other
regressioncoefficient
of +0.602 estimatedin this stations(Fig. 4, 5, and 6), some adverseenvironregressionis less thanthe serial correlationof the mentalinfluenceis indicatedsince the decreasing
growth deviations themselves (+0.70 for the growthpatternis contraryto normalgrowthexperiod 1911-58 or +0.81 for the longer period pectations.
startingin 1680), but it illustratesthe significant The marked negative departurefrom normal
effectof previous year's growth on the current for 50- to 99-year-oldhealthytrees adjacent to
year's growth.
and withinpole blight areas is particularlynoComparisonof growthpatterns.withinage and ticeable (Table 3). Althoughthe diseased trees
healthclasses.-The relativegrowthofthevarious- had a patternsimilarto theirhealthycounterparts
aged trees in different
time periods furtherillus- for their first3 decades, they apparentlynever
tratestheadverseeffectofthelast 50 years'climate recoveredsufficiently
fromthe most criticaldecon treegrowth. All age classes shownin Table 2 ade (1929-38) to maintaincomparablegrowth.
grew more slowly duringthe last 50-yearperiod Once they became diseased, their growthdrasti(1909-58) than in the preceding50-yearperiod cally droppedoffas indicatedby the fifthdecade
(1855-1904).
(1949-58).
2. Differences between average decadal relative
growth 1909-58 and the 50-year average of the same
trees for the period 1855-1904
TABLE
Tree age
in 1958
1909-18
1919-28
1929-38
1939-48
1949-58
200+
150-199
100-149
0.121
- .080
.057
-0.081
- .287
- .022
-0.079
- .338
- .037
-0.069
- .185
.037
-0.136
- .215
- .052
Average
difference
1909-58
-0.049
- .221
- .003
Early growthpatternsof trees in several age
classes provide insightinto the conditionsthese
trees experiencedprior to and during the time
they would have been susceptibleto pole blight.
Time periods were selected to representthe 50
years startingwhen all treesin the age class were
at least 10 years old. Average deviationsfrom
normalgrowthforeach age were calculatedfor 5
succeedingdecades (Table 3). It is clear that
the 1909-58 period (representedby "all healthy"
trees in the 50- to 99-year-oldclass) was less
favorableforgrowththan the first50-yearperiod
in thelives of treesrepresentedin any of thethree
otherage classes. The mean relativegrowthof
the first50 years has decreasedin successionfor
each of the three age classes originatingsince
1714 (last column,Table 3).
Within the 50- to 99-year-oldclass, average
growth of trees for the 5 decades from stands
STOCHASTIC
INTERPRETATIONS
We have answeredthe firstof our two introductoryquestions. Specifically,we have shown that
thepole blightdisease apparentlyis a consequence
of adverse climateinteractingwith site factorsat
a criticalstage in the developmentof the tree or
stand. The manager'sinterestin our secondquestion concerningthe probabilityof pole blightrecurrencecan be consideredfromtwo aspects: (1)
Is there evidencefor a cyclicoccurrenceof such
adverseclimate?and (2) What is the probability
that a year as unfavorableto growthas 1936 occurs during the critical pole stage of a stand's
?
development
Answersto thesequestionswere soughtthrough
spectralanalysis of the 283 deviationsshown in
Fig. 3A. The spectrumshown in Fig. 7 can be
consideredas an analysis of variance testingfor
periodicityin the time series of deviations. The
total area coveredby all bars representsthe total
varianceof the deviations. Thus, the area of each
bar representsthe portion of the total variance
associated with the periodicityover which each
is plotted. Peaks in this diagramwould indicate
a tendencyforsequencesof adverse (and likewise,
interveningfavorable) conditionsto appear periodicallywith an intervalindicatedby the abscissa.
CHARLES
236
AND ALBERT
D. LEAPHART
Ecology, Vol. 52, No. 2
R. STAGE
3. Comparison of early growth patterns of four age classes of healthy and diseased trees growing in differing
proximityto pole-blighted (PB) stands,
TABLE
Disease
proximity
class
Age class
in 1958
Time period
1714-1763............
1790-1839............
1855-1904............
1909-1958............
44
25
35
42
73
50
165
52
Adjacent PB stands
Adjacent PB stands
Adjacent PB stands
OutsidePB area
Adjacent PB stands
TnPB stands
All healthy
Diseased trees
200+
150-199
100-149
50-99
5
Average
deviation
for
5 decades
0.071
-.071
-.139
-.097
-.265
-.256
-.219
-.597
0.201
-.074
-.149
.0530
-.235c
-.274
-.175a
-.358
in time periodb
Decades
No.
trees
1
2
0.183
-.124
-.036
.137?
-.0640
-.096
-.033a
-.089
0.192
-.071
-.156
.117
-.248
-.271
-.162
-.311
3
4
(Averagedeviation)
0.284
0.278
-.070
-.032
-.177
-.236
.021
.087
-.189
-.408
-.262
-.485
-.157
-.305
-.323
-.471
aAll treeshealthyexceptthe 52 comprisingthe last line.
bFirstgroupbeginningwith all treesin the age class at least 10 years old.
cAdjustedbecause tree numbervaried fromstart to end of decade.
0.602 a_1.
abB series has been exthe
of
scale
vertical
The
panded so thatboththe A series and the B series
have the same apparentstandarddeviation.
the
The next step of the analysis transformed
B series into a series of normallydistributeddeviationshavingzero meanand unitvariance. This
step was accomplishedby plottingthe ordered
deviationsof the B series againsttheircumulative
probabilityon normalprobabilitypaper (Fig. 8).
FIG. 7. Power spectrum of the series of deviations Then, a straightline was drawn on this graph to
drawn in Fig. 3A. Vertical scale is the product of power
representthe desired normal distribution. For
times frequency. Horizontal scale is logarithm of frequency. Hence, areas under the spectrumare proportional each elementof the B series,the normal deviate
havingthe same ordinatewas read offthe upper
to variance.
scale of Fig. 8 as indicatedby the arrowsfor one
Several studiesof treeringshave been analyzed example. The unbiasedestimateof the serial corin this way, lookingfor evidenceof a periodicity relation (for a lag of 1 year) of the normalized
associatedwiththe 11-yearcyclein sunspots(e.g., series was 0.19. The probabilitydistributionof
charBryson and Dutton 1961, Matalas 1962). No 60-yearminimafroma normaldistribution
peak occurs at 11 years in the spectrumof these acterizedby serial correlationof 0.19 was derived
transFig. 2. This distribution,
westernwhite pine trees to indicate a response fromGringorten's
to the sunspotcycle. Rather,the variance seems formedback to growthdeviates,is drawn on an
probabilityscale in Fig. 9.
to increase fairlysteadilywith increasingperiod extreme-value
indicatesthata delength. The trendof variance is approximately This probabilitydistribution
proportionalto the one-fourthpower of the pe- viationof theB seriesas low as or lowerthanthat
riodicity. For comparison,Bryson and Dutton of 1936 occurs at least once in 60 years with an
(1961) reportthat somewhatgreaterproportion estimatedprobabilityof less than 0.01. The corof thevarianceof theirsequoia seriesis associated respondingprobabilityfor the 1922 low is 0.10;
and forthe 1931 low, 0.14.
withshorterperiodicities.
If pole blightcould be triggeredon a particular
To answer the question concerningthe probability distributionof climatic fluctuationsfrom site by a climaticallyextremeyear, such as 1922,
so thatthe duringa criticalstage of 60 years in the life of a
yearto year,the data weretransformed
model and resultsof Gringorten(1966) could be stand,then the probabilityof 0.10 indicatesthat
that about one-tenthof the stands regeneratedin the
used. First, the serial correlationcoefficient
is attributableto stored foods, enhanced foliage course of managinga forestwith an even distridevelopment,and other physiologicalbases was butionof age classes would be affectedwith this
removedfromthe sequence of deviations. Ac- disease. For a forestmanagedon 120-yearrotacordingly,a new series of deviations (Fig. 3B) tion such an eventwould affecthalf (60/120) the
was computedfromthe originalseries (Fig. 3A) forestcharacterizedby the particularsite quality.
On a bettersite,perhapsa deviationas greatas
in the
by using the serial correlationcoefficient
that
experiencedin 1936 would be required,and
formula:
_
D
700
3<
i
100
00D
50
40
0
20
11 10
(Ye--)
PERIODICITY
7
6
4
3
2
CLIMATE AND POLE BLIGHT DISEASE
EarlySpring1971
NORMALIZED DEVIATE
-3
-2
0
-1
1
2
3
.9995.
.999
.998
.995
*991
.98
.95.
.90
>
of Deviations
in Figure
_Distribution
.70
I-
3D.
.60;
0
.80
.cc
.301
.000
.005
.0:.
.9'1
DIscussIoN
.002
.00
.0051
-0
-30.4
.2
-0.
-1 0
.20
-0.1
seiestrinuFig.
FrbaiG.i8. Diagramoused ton tansfotreme-thle
sBcoa
237
affectedwhen the event occurs. Thus, half the
forestarea in thatsiteclass would be damaged.
Obviously,a singleadverse year does not trigger pole blight. More likely,a series of adverse
years occurringin close proximityin time is required. Therefore,the probabilityof occurrence
of the disease is greatlyreduced. For example,
if 6 consecutiveyears at least as bad as 1935 to
1940 or 1952-1957 (be... bi+50.5) define
the criticalevent,thenthe probabilityof thisevent
occurringin a 24-year period is reduced to less
than0.025, or about one in 40.
The relativelylargeproportionof varianceassociated with componentsof the long period displayed in the spectralanalysis may indicatethat
extremedeviationsare likely to be clusteredin
time to a somewhatgreater degree than would
characterizethe model used by Gringorten. The
such a clusterin which
period 1916-40 exemplifies
only4 of the 25 years reachedthe overall average
level of growth (Fig. 3B). There is a chance
that similarclusterswill occur in the futurewith
pole blightas a consequence,but our recordsare
inadequateto establishestimatesoftheirfrequency.
Thus, the above probabilitystatementsshould be
consideredas firstapproximationsto be revised
as currentweatherbecomesclimate.
oralty
thenless than 1% of the standsregeneratedmight
be afflicted.However,if all age classes up to 120
were equally representedon the site,those in the
hypothesizedcritical60-year age span would be
Westernwhitepine regeneratesreadilyon most
sites (withinits range) denudedby fire,man, or
other natural catastrophes. Consequently,under
circumstances favorable for germination and
growthin years past (1853-82, Fig. 3A), our
currentpole stands originatedon a wide variety
of sites. When these stands reached an age of
40-80 yearson some ofthesesites,especiallythose
with low moisture-storage
capacity,exceptionally
adverse circumstancesinduced criticalphysiological stresses. The result was not only reduced
growthof trees,but abnormalmortalityas well.
of the pole blight disease in
Our interpretation
westernwhitepine is based on an analysisof the
growthrings of the trees,on analysis of studies
of the root system(Leaphart 1957, Leaphart and
Wicker 1966, and McMinn 1956) in relationto
treegrowth,and on the correlationof tree growth
and availwithclimate,predominantly
temperature
able moisture. Since we are also convincedthat
the tree-ringrecordof westernwhitepine reflects
the relativeseverityof its climate,we have singled
out one period (1916-40) thatrepresentsthe most
adversegrowthconditionswithregardto intensity
and durationin the last 280 years.
We findno evidencefromtree-ringpatternsto
mature(200 ? 70 years)
indicatethatpresent-day
stands sufferedgrowthdepressionin their early
238
CHARLES
D. LEAPHART
AND ALBERT
R. STAGE
Ecology, Vol. 52, No. 2
life,nor do we findfrompresentstand structure the chain of events which ultimatelyresultedin
and compositionthat these stands experiencedan pole blight. Althoughthe hazard ratingof these
abnormalamountof mortality,such as would be sites forthe occurrenceof pole blightwill always
representedby an epidemicof pole blight. For be high (Leaphart 1958), the probabilityof disexample, Deception Creek ExperimentalForest ease reoccurrence
appears to be low fromour calin northernIdaho and the Hiatt Creek drainage culations. If the climateof the period from1916
of northwestMontana containfullystocked,ma- to 1940 does not representa permanentshiftto
ture westernwhite pine stands adjacent to pole- less favorablegrowth conditionsand if western
sized stands in which most westernwhite pine white pine is favored for regenerationonly on
then
characteristics,
treeswere killedor affectedby pole blight. Else- sites of low moisture-stress
where in the westernwhite pine type, one finds chancesare veryfavorablethatpole blightwill not
the remnantsof what probably were relatively reoccurformanycenturies.
dense stands of westernwhitepine, but theyare
Conversely,a continuingadverse climaticpatnear-climaxstands of cedar, grand fir,or hem- ternwould drasticallyincreasethe predictedproblock with a few stately 200+-year-old western abilitiesof pole blightoccurrence,since clusters
of dry years would be both more frequentand
whitepine treesper acre.
Our knowledgeof the historiesof these latter moresevere. Evidence of even warmerand drier
stands is conjectural. Even thoughour tree-ring periods than ours of 1916-40 is recorded from
records to 1680 suggest that no severe drought studies of glaciation (Mathews 1951, Heusser
was experiencedin early life of maturewestern 1956, Goldthwait1966), of sea levels (Jelgersma
whitepine stands,we have not ruled out the pos- 1966, Milliman and Emery 1968), and of vegesibilitythat pole blight may have started such tationalsuccessions(Hansen 1947,Heusser 1956).
standstowardtheirpresentlow numberof stems As experiencedin the BritishIsles (Lamb 1965),
per acre. On the otherhand, those stands could these periods drasticallyaffectedagriculturalachave startedwith a low densityof westernwhite tivities,and one lastingabout 200 years occurred
pine or could have been decimated by a bark around 1100 A.D., a relativelyrecentevent. Albeetleepidemicsuch as occurredin the late 1930's thoughour tree-ringrecordand a similarthough
and 1940's or occurs today in maturestands on longerone of Keen's (1937) show no such long
the St. Joe and ClearwaterNational Forests.
periods,such eventscould neverthelessbe meanGrowth in all age classes, though tendingto ingfulin termsof thelong lifeof mostforesttrees.
recoverin the late 1940's and early 1950's, still Lamb (1965) aptly states, "A table of statistics
was below normal in 1958. In that year also, can never be substitutedfor a forecast,"but the
of recurrenceof even the shortadverse
Leaphart (1959) reported drought damage in probability
young western white pine stands in the Priest periodspredictedfromour recordsprovidesmanRiver valley,and some of these same areas suf- agementwithits mostplausiblebase forassessing
fered similar droughtsymptomsagain in 1967. the hazardof pole blightto westernwhitepine.
Pole blightstill manifestsitselfin the pole stands
ACKNOWLEDGMENT
surveyedin the early 1950's (Graham 1958b).
Some stands found in 1956 to be very lightly The authorssincerelyappreciatethe assistanceof Dr.
had Ed F. Wicker,ForestrySciences Laboratory,Moscow,
blighted(e.g., Hiatt Creek) withno mortality
by 1967 experiencedconsiderablespread of the Idaho, who helpedcollectthe core and disc samplesand
disease and had sufferedmoderate damage and measuredall annual rings (76,000+) used in this study.
mortalityfromit. Still, some blightedstands of
CITED
LITERATURE
the late 1940's (e.g., at Priest River Experimental
Bryson, R. A., and J. A. Dutton. 1961. Some aspects
Forest) seem to have passed the stage of disease
of the variance spectra of the tree rings and varves.
expression. Although most affectedtrees have
Ann. N.Y. Acad. Sci. 95: 580-604.
died, a few survived;these,along withthose that Daubenmire, R. F., and Jean B. Daubenmire. 1968.
did not develop symptoms,now appear healthy, Forest vegetation of eastern Washington and northern Idaho. Wash. Agr. Exp. Sta. Tech. Bull. 60.
but show the reduced growth pattern of trees
104 p.
withinpole blightareas (Table 3). These trees, Duff, G.
H., and Norah J. Nolan. 1953. Growth and
like the older trees of maturestands,apparently morphogenesis in the Canadian forest species. I.
The controls of cambial and apical activity in Pinus
are past the susceptiblestage now.
resinosa Ait. Can. J. Bot. 31: 471-513.
The one known epidemic of pole blight was
of parameters in timecoincidentwith and followedthe droughtperiod Durbin, J. 1960. Estimation
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identified
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Early Spring 1971
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