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United States Effects of Thinning on
Department
ofAgriculture
Temperature Dynamics and
Forest Service
IRnetseeramrocuhntSatiantion l\/lountain Pine Beetle Activity
Research Paper a Lodgepole Pin^ Stand
INT-RP-479 in
December 994
1
The Authors Research Summary
Dale L. Bartos is an ecologist with the Mountain Temperature measurements were made to better
Pine Beetle Population Dynamics researchwork understand the role ofmicroclimate on mountain
unit, Intermountain Research Station, Logan, UT. pine beetle,Dendroctonusponderosae Hopkins
Prior tojoining the unit in 1984, he was with the (Coleoptera: Scolytidae), activity as a result of
Intermountain Station as a member ofthe aspen thinninglodgepole pine stands. The study area is
ecosystem project for 12 years. He holds B.S. and on the north slope ofthe Unita Mountain Range in
M.S. degrees from Fort Hays State University, northeastern Utah. Samplingwas done over 61
Hays, KS, and a Ph.D. degree in range science from days startingJune 23, 1987 (174). Eight lodgepole
Colorado State University. His principal research pines,Pinus contorta var. latifolia Engelm., were
interests are in ecological processes and disturbance sampled for surface and subsurface (phloem) tem-
ecology. peratures in a thinned and unthinned stand. Prin-
Gordon D. Booth (retired) was leader ofthe Statis- cipal components analysis was applied to all tem-
perature variables. Most ofthe variation was
tics and Computer Sciences Group for the Inter-
mountainResearch Stationin Ogden, UT. Hereceived attributed to two variables, coolest part ofthe night
(1:00 a.m. to 9:00 a.m.) and hottest part ofthe day
a B.A. degree in 1960 and a B.S. degree in statistics
in 1963, bothfrom BrighamYoungUniversity, Prove, (1:00 p.m. to 6:00 p.m.). These two variables were
UT. Then he was granted an M.S. degree in 1967 smoothed using time series analysis that permitted
and a Ph.D. degree in 1973 in statistics from Iowa us to see general patterns and small differences
State University. From 1963 to 1965, he worked as betweentree temperatures. The thinned stand
was approximately 1 °C warmerthantheunthinned
consulting statistician with U.S. Steel Corporation
and with Philhps Petroleum Co. From 1967 to 1981 stand andthe day temperature was 10 to 11 °C
higher than the corresponding night temperature.
he worked as consulting statistician with theAgri-
Models were developedto predict phloem tempera-
cultural Research Service, U.S. Department of
Agriculture. From 1981 to 1994 he was with the ture from bark surface temperature. The resvdtant
equations had values of0.98 or greater.
Intermountain Research Station.
The use oftrade orfirm names in thispaper isforreader
information only anddoes not implyendorsement by the
U.S. DepartmentofAgriculture ofanyproductorservice.
IntermountainResearchStation
324 25thStreet
Ogden, UT84401
Effects of Thinning on
Temperature Dynamics and
Mountain Pine Beetle Activity
a Lodgepoie Pine Stand
in
Dale L. Bartos
Gordon D. Booth
Introduction the stand, and (2) growth ofresidual trees is usually
slowto respond to thinning. The objective ofthis
Thinning has been usedin the pastto increase study was to determine the surface and subsurface
tree vigor (Graham and Knight 1965; Keen 1958), barktemperature variabilitybetween thinned and
and tree resistance to attacks by mountain pine unthinned lodgepoie pine forest and to relate these
beetle. The removal oflarge-diameter lodgepoie differences to mountain pine beetle activity.
pines, which are preferred by mountain pine beetle,
can also resultin a reduction in tree loss during
Methods and Materials
beetle epidemics (Cahill 1978; Cole and others 1983;
Hamel 1978; McGregor and others 1987). Reduced
tree losses occur before residual trees can express The study site is south ofMountain View, WY,
resistance by increased growth (Amman and others on the north slope ofthe Uinta Mountains in north-
1988). This phenomenon suggests that factors other eastern Utah. Mature lodgepoie pine (80-120 years
than vigor may be responsible forreductions in old) occupy the site, which is on the Wasatch-Cache
mountain pine beetle infestations. National Forest at an elevation of2,865 m. Part of
Thinningforests can cause subtle changes in tree the site was thinned in the early 1970's. Replicating
physiology (Nebeker and Hodges 1983) and microcli- the thinningtreatment was not possible because of
mate, especially temperature (Bartos andAmman the length oftime since treatment and the prohibi-
1989; Schmid and others 1992). In western North tive cost ofequipment to monitor numerous sites.
America, changes brought about bythinninglodge- We decided that useful information could still be
pole pine (Pinus contorta var. latifolia Engelm.) for- obtained by selecting adjacent stands (thinned and
ests have had profound effects on mountain pine unthinned). These two stands were selected so that
beetle (Dendroctonusponderosae Hopkins [Coleop- physical characteristics, such as slope, aspect, and
tera: Scolytidae]) behavior(Schmitz andothers 1989), elevation were uniform.
resultinginreducedtree mortalityinthinned stands The stands were sampled for 61 days duringthe
(McGregor and others 1987). summer of1987 to determine bole's surface and sub-
In addition to increasing growing space, thinning surface (phloem) temperature. During 1986 the
also affects parameters ofthe physical environment, area had a very active mountain pine beetle infesta-
such as temperature, light, and wind speed. Tem- tion andwasused foranin-depthstudyofnumerous
perature is an important factor in the ecology ofin- microclimatic differences including; temperature,
incident solar radiation, windspeed, wind direction,
sects as it affects the physical conditions ofhabitat
and the physiology ofinsects themselves (Safranyik and stand temperatures (Bartos and Amman 1989).
1978; Wellington 1950). In the case ofmountain Beetles were captured during peak flight time in
pine beetle, observations were made on the effects both thinned and unthinned stands in 1986; only
ofextremely high (Patterson 1930) and low (Somme 5 percent ofthe total beetles caught were in the
1964; Yuill 1941) temperatures. Between the ex- thinned stand. The epidemic beetle population
tremes is an optimum zone oftemperature that may was not active during the summer of1987.
be modified by other microclimaticfactors (Rudinsky
Stand Characteristics
1962).
We
explored the effects oftemperature on altered Characteristics ofthe thinned and unthinned
lodgepoie pine stands because (1) temperature lodgepoie pine stands were determined through
changes are immediate followingtree removal from variable plot (10 BAF) cruising. Plots were placed
1
m
50 apartin a grid patternin each stand. Lodge- These means were labeled: 1:00 a.m., 4:00 a.m.,
pole pine trees on each plotwere tallied as to live or 7:00 a.m., 10:00 a.m., 1:00 p.m., 4:00 p.m., 7:00 p.m.,
dead by cause ofdeath and were measured for diam- and 10:00 p.m. The mean labeled 1:00 a.m. was the
eter at breast height (d.b.h.). The dominant or co- average ofthree temperature measurements taken
dominant tree closest to plot center was measured at 1:00 a.m., 2:00 a.m., and 3:00 a.m. Other means
for height and crown length. Stand density was ex- are defined similarly. The measurements were
pressed in terms ofbasal area andnumber oftrees taken each day for 61 days.
per hectare. Afurther reduction inthe number ofvariables
that needed to be dealt with was attempted by using
Monitoring Temperature a modificationofprincipal component analysis, some-
what similar to that used by Jassby and Powell
An automatic recording device (2IX micrologger, (1990). The objective was to identify fewer than
Campbell Scientific) was used to measure the tem- eight daily means that would capture all the essen-
peratures for a 61-day period startingJune 23, 1987 tial information on dailytemperature patterns.
(174). This time period encompassed the "peak" Suchvariables would also have the additional prop-
mountain pine beetle flight period, which usually erty ofbeingindependent and thus capable ofbeing
occurs in this area the lastweek in July and the studied one at a time.
first week inAugust (Bartos andAmman 1989). The principal components analysis indicatedthat
The time priorto flight was included to monitor the onlythe first two principal components accounted
temperature that existed duringthe final stages of for virtually all the variability within a given day.
beetle maturation. Eight trees were monitored in Further, the first principal component was essen-
each ofthe two treatments. Initially, the instru- tiallythe mean ofthe mean temperatures labeled
menttower site was randomly selected within each 1:00 a.m., 4:00 a.m., and 7:00 a.m. We chose to use
stand. The eight sample trees were located around a simple unweighted mean ofthese three tempera-
this tower and the distance fi'om the tower to each tures and referto it as the nighttime mean tempera-
sample tree was limited by the temperature sensor ture. Likewise, the second principal componentwas
"leads." All sample trees were similar in height, essentially the mean ofthe mean temperatures at
crown length, and d.b.h. (approximately 22 cm). 1:00 p.m. and 4:00 p.m. Again, we chose to use the
Temperature sensors were connected to the micro- simple mean ofthese two temperatiires to represent
logger to measure temperature attwo points on the second principal component and refer to it as
each sample tree. These temperature sensors were the daytime mean temperature. Because ofthe
m
placed at breast height (b.h.) 1.3 aboveground, close relationships between these two variables
on the bark surface, and immediately below the sur- and the first two principal components, the two
face, on the south side ofthe trees. Temperatures variables are very nearly independent at any given
measured in these stands in 1986 (Bartos 1988) time. Ofcourse, they are not serially independent
showed that a strongrelationship existed between
overtime (Booth 1993).
the surface temperature on the north and south The nighttime and da3i;ime mean temperatures
side ofthe tree. Therefore, only the south side was were analyzed as time series. We knew in advance
measured to maximize the number ofsample trees. thatthere was variability from one measurement to
The below-outer bark surface sensor was posi- the next duringthe course ofthe 61-day study. To
tioned in the phloem because phloem is the substra- study the underlyingtemperature patterns, we ap-
tum in which mountain pine beetle adults mine and plied the Daniell (1946) window, a smoothing pro-
lay eggs and the developinglarvae use it as food. cess, to each ofthe time series.
This sensor was placedjust below the thinmbmark of The application ofthis smoothing method elimi-
the tree and was gently forced a couple of into nated all high frequency oscillations. Residuals
the phloem.
fi'om these smoothed values had all major, low-
frequency patterns removed, and a fourier analysis
Data Analysis
ofthem produced no detectable periodicities in the
data. Therefore, graphs ofthe smoothed values
Characteristics (density, basal area, d.b.h., tree
height, and crown length) ofthinned and unthinned themselves can be expected to convey all pertinent
stands obtained during stand surveys were sub- information relatingto temperature patterns inthe
jected to analysis ofvariance to test for significant data.
differences between treatments (Bartos andAmman Schmid and others (1992) found a strong correla-
1989). tion between bark temperature and ambient air
Ourbasic daily data consisted ofeightvalues, temperature. Ifpossible, we were interested in es-
each being the mean ofthree hourly measurements. tablishing a relationship between bark temperature
2
m
and phloem temperature. Therefore, we performed 15.1 high, withUvecrownbeing53 percentoftotal
model fitting on 61 nighttime means and on 61 day- height (Bartos andAmman 1989). Ofthese stand
time means. We further dividedthe data into those characteristics, only the basal area andtrees per
obtained on the thinned stand and those obtained hectare were significantly different between stands
—
on the unthinned stand. Thus, we obtained atotal (P < 0.05) at this point in time approximately
offour fitted models: both a nighttime and daytime 20 years after thinning. When the stands were
model forthe thinned steuid and two analogous monitored, the effects ofthe treatmentwere still
models forthe unthinned stand. The models were pronounced.
fitusing data fi-om five trees in the unthinned stand
and fi-om fourtrees in the thinned stand. These Temperature
trees were selected because the remainder ofthe
The three main questions ofinterest regarding
eighttrees produced incomplete data sets.
temperature dynamics are: (1) "Whatis the differ-
ence intemperature pattern betweenthe thinned
Results and the unthinned stands?", (2) "What is the differ-
ence in pattern betweenthe air temperature and
We looked atthe results interms ofboth stand the phloem temperature?", and (3) "What is the dif-
characteristics andtemperature. ference in patternbetween the temperatures atthe
warmesttime ofthe day andthose at the coolest
Stand Characteristics part ofthe night?" Data relatingto these questions
appearinfigures 1 to 3, respectively.
Thethinned stand had an average basal area of
To facilitate answeringthese three questions, the
22.1 m^/ha, a density of708 trees/ha, and an aver- datawerebroken into four groups: measurements
age d.b.h. of20.2 cm.mDominant and codominant taken in the airin the thinned stand (AT), inthe
trees averaged 15.1 in height, with live crown phloem inthe thinned stand (PT), in the air in the
being 52 percent oftotal height. The adjacentun- unthinned stand (AU), andinthe phloem in the
thinned stand had a basal area of37.0 m^/ha, a unthinned stand (PU). The measurements inAT
density of1,090 trees/ha, and an average d.b.h. of and PT are fi-om the sametrees in the thinned
18.6 cm. Dominant and codominanttrees averaged
Unthinned Stand Thinned Stand
M M M
1'7l4IIrIIIIIIIIIII II1IIIIIIIII210I4I1IIIIIIII IIII II 23I4
Days — — Days —
AU Day PUDay AUNight PUNight ATDay PTDay ATNight PTNight
—
Figure 1 Smoothed curves showing treatmentdifferences for61-daytime period
between June 23 and August22, 1987. Sets of curves representthe hottestand
coldestpartofthe day. First letterofthe code refersto position oftemperature probe
(A = airand P = phloem) and second letter refers totreatment (T= thinned and U =
unthinned).
3
Air Temperatures Phloem Temperatures
174 204 234 174 204 234
— Days — — Days —
AT Day AU Day ATNight AUNight PTDay PU Day PTNight PU Night
—
Figure2 Smoothed curves showing temperature differencesfor61-daytime period
between June 23 and August22, 1987. Sets ofcurves representthe hottestand
coldest part ofthe day. First letterofthe code refersto position oftemperature probe
(A = airand P = phloem) and second letterrefersto treatment (T=thinned and
U = unthinned).
Night Temperatures Afternoon Temperatures
Days — Days
—
AT PT AU PU PT PT AU - PU
—
Figure3 Smoothed curves showingtemperaturedifferences ofthe hottestand coldest
part ofthe dayfora 61-daytime period between June 23 andAugust22, 1987. First
letterofthe code refers to position oftemperature probe (A = airand P =phloem) and
second letterrefers totreatment (T= thinned and U = unthinned).
4
stand and, thus, are paired. Likewise thoseinAU Table 1—Percentagesoftotal day-to-dayvariability
and PU are from the same trees inthe \inthinned explained byeigenvalues in principal component
stand and are paired. These groupings are main- analysis.
tainedthroughoutthe analyses and resulting
Percentofday-to-dayvariability
graphs. Datagroup Night Day Cumulative
A
fourth question ofinterestregards the tempera-
AT 66 25 91
ture increase from the coolest part ofthe nightto
(thinned stand
the warmest part ofthe afternoon. These increases
on surface)
are presented in figure 4.
Two variables (principal components) accounted PT 68 25 93
for high percentages ofthe variability in tempera- (thinned stand
ture from day to day (see table 1). Therefore, only in phloem)
these two variables were studied. The firstis the AU 69 24 93
warmestpartofthe afternoon(1:00 p.m. to6:00 p.m.), (unthinned stand
whichis referred to as the "day"variable, andthe on surface)
secondis the coolest partofthe night (1:00 a.m. to PU 69 24 93
9:00 a.m.), which is the "night" variable. The high (unthinned stand
percentages shown intable 1 indicate that ifthe ac- in phloem)
tual principal component had been used, complete
independence would have resulted. However, this
would have requiredusing a different weighted
mean for each ofthe four datagroups. Because the comparable. Figures 1 to 4 contain the smoothed
weights (coefficients from the principal components values ofthe day and night means.
analysis) were quite similar for the hours specified Afinal point ofinterestwas the development of
in"day" and also in "night," unweighted means for models to predict phloem temperature from bark
the appropriate hours were used in all analyses. surfacetemperature. The estimates ofvariance for
This makes the variables from the fourdata groups the fitted models were based on means ofseveral
trees. Because we wishedto predict phloem tem-
perature for anindividual tree and because the vari-
ance is larger for an individual tree than for a mean
Temperature Increase During Day
ofseveral trees, we inflated these variances to re-
flect proper prediction intervals on an individual
treebasis. These intervals are presentedinfigure 5.
The resultingmodels (table 2) show there is a
strongcorrelation (r^> 0.98) between bark surface
and phloem temperatures.
—
Thinned vs. Unthinned Temperature curves
for the 61-day period were very similarbetween the
thinned and unthinned stands (fig. 1). Similar pat-
terns were obtained forboth the hottest and coldest
part ofthe day forboth the thinned andunthinned
stands. Subsurface (phloem) temperatures were
similarto those onthe bark surface (air).
Inthe unthinned stand the airtemperature was
higher than the phloem temperatiire duringthe day
234 with a reversal occurring at night.
Inthe thinned stand, the same general condition
held with the exceptions that for most ofthe month
— ofJulythe phloem temperature duringthe day was
Figure4 Smoothed curves showing warmerthanthe airtemperature. This phenom-
temperature increasesfrom the coldestto enon probably canbe attributed, in part, to overcast
the hottest partofthedayfora 61-daytime
skies duringthis period. The thinned stand was
period between June 23 and August22,
more open; therefore, atmospheric conditions could
1987. First letterofthe code refersto
position oftemperature probe (A = airand have amore subtle effect on the temperatures, such
P = phloem) and second letter refers to as increase in radiant warming. Another condition
treatment (T= thinned and U = unthinned). in the thinned stand was the larger difference
5
Predicted Phloem Temperature Predicted Phloem Temperature
Thinned Stand during Day Thinned Stand at Night
30
30 T-
c: 25 25 -
ro 20 2
QCC)L 0Q).20
c E
<D 15 15 -
\- 1-
E(oU 10 E(oU 10 -
sz 5 5
D. Q.
-
10 15 20 25 30 10 15 20 25 30
AirTemperature AirTemperature
Predicted Phloem Temperature Predicted Phloem Temperature
Unthinned Stand during Day
Unthinned Stand at Night
30 30
T-
25
2
20
Q.
E
a> 15
h-
E
10
o
JZ 5
Q.
-
10 15 20 30 10 15 20 25 30
AirTemperature AirTemperature
—
Figure5 Plots ofvarianceassociated with modelsdeveloped to predictphloem temperature from
barksurface temperature. Treatment/time represented are (A) thinned/daytime, (B) unthinned/
daytime, (C) thinned/nighttime, and (D) unthinned/nighttime.
—
Table2 Equationsthatpredictphloem temperaturefrom between phloem and airtemperatures at night.
barksurfacetemperature forfourtreatment/time This was due to a consistently higher night-time
situations. phloem temperature inthe thinned stand. Overall,
the measuredtemperature inthe thinned stands
Treatment Predictiveequation
was warmerby about 1 °C. This difference does
Thinned y= 0.81324 + 0.96285*ear/cSt;r 0.9871 not appearlarge; however, ifaccumulated over a
night period oftime itcould have an effect on beetle
Thinned 9= 0.81383 + 0.9534Q*BarkSur 0.9798 development.
day —
Airvs. Phloem Graphs oftemperature inthe
Unthinned y= 0.28213 + 0.90000*ear/cStyr 0.9986 air displayed similar patterns in both day and night
night measiu'ements (fig. 2). The curves for nighttem-
Unthinned y==0.4105 + 0.96250*ea/-/cSur 0.9973 perature contain smoother and less volatile pat-
day terns. Nevertheless, the same general patterns pre-
vail in both sets ofmeasurements. While the night
6
