Gene D. Amman
Bruce H. Baker
MOUNTAINPINE BEETLE
INFLUENCE
ON LODGEPOLE
PINE STANDSTRUCTURE
ABSTRACT--EfJorts to control populations o[ mountain
pine beetle (DendroctonusponderosaeHopk.) in lodgepole
pine (Pinus contorta Dougl.) were evaluated /rom tree
diameter
distributions
within
treated and untreated
stands.
Beetle populations, where in[estation period was complete,
declined in approximately the same number o[ years, and
lodgepole pine survival in the two types o[ stands was
comparable. However, suppressionmeasuresdid slow the
rate o[ tree mortality in two stands still under attack. Mixed
standso[ up to 36 percent trees o[ other specieswere proportionally as susceptible to beetle in[estation as those
having lessthan 10 percent trees o[ other species.Survival
increased with elevation, apparently because o[ adverse
efJect o[ temperature on beetles.
THE AUTHORS
are, respectively,research entomologist,Intmtn.
Forest and Range Exp. Sta., and entomologist,Div. of Timber
Management, Intmtn. Region, U.S. Forest Serv., Ogden, Utah.
high rate of reinfestationin stands where control of
beetle populationshad been conducted.
If beetie control methods are to be evaluated, their
effectsmust be analyzedfor an entire infestation,period? Assessmentmust be based on comparisonsof
treated and untreated stands. Data must include: (1)
ratesof tree mortality and (2) residualvolumes.
During late summerand early fall of 1969, blocksof
lodgepolepine were sampledwithin the Teton-Targhee
area. The pu.•posewas to evaluatebeetie suppression
attempts.
Residualstand structuresin treated and un•' hemountain
,pine
,beetie
(Dendroctonus
ponderosae
treated
areas
were analyzedand comparedand, ,when
Hopk.), one of the most aggressive
of the ,barkbeetles,
possible,
tree
mortality rates were also considered.No
k:.ffismost of the large, dominanttrees in a stand of
attempt,wasmade to determine.whethercontrol efforts
lodgepolepine (Pinus contorta Dougl.) before an inreducedor preventedthe spreadof infestation.Little is
festation declines (Fig. 1). Moreover, .infestationsreknown of the flight habitsof the beetle;so .thequestion
cur (as in westernWyoming and southeasternIdaho),
remainsas to whether•populations
,buildup in one stand
and as a result of each suchreoccurrence,la,rgesums
are expendedon attemptsto controlthe insect.
The mostrecentbeetleoutbreakin westernWyoming
began in the late 1950's. Approximately 1.3 million
trees on the Teton
National
National
Forest
and Grand
Teton
Park were treated or harvested for mountain
pine beetie control .,between1957 and 19682 The
effort,waseven greateron the TargheeNational Forest,
Idaho; over 1.7 million lodgepolepine were chemically
treated or harvestedfrom 1962 throughthe spring of
1969.
Methods of evaluatingforestinsectinfestationshave
been describedby Knight (11), and controlproced•tres
have been reviewed,byBalch (2). However, the literature offersno satisfactorymeans of assessing
the effects
of bark beetle control.
Earlier
efforts to evaluate
the
effectivenessof control jobs usually were based on
beetleinfestationratesfor shortperiods(a year or so)
insteadof on standstructureduringan entire infestation
period(4, 8, 12).
Chemicals sprayed on infested trees kill beetles
beneath the bark (7, 9, 14), .reducingthe beetle
population. However, as Kinghorn (9) noted, the
amountof damagedone to a standby survivingbeetles
is unknown. Moreover, such treatmentsmay not halt
the outbreak. Klein and McGregor (10) reported a
•Ethylene dibromide in diesel oil (EDB)
trunks.
204
sprayed on tree
and then move to others, or whether conditions favor
the buildup of populations in a number of stands
simultaneously.
The 10 areaschosenfor study are typical of beetleinfestedstandsthroughoutthe Teton National Forest
and Grand Teton National Park, Wyoming, and the
Targhee National Forest, Idaho. Areas in which the
infestation had run its course were desked. However,
only six met this criterion; the other four were still
under attack.
Standsof trees on the sampledblocksqualifiedas
pure or mixed merchantablelodgepolepine, although
loggingwas not alwaysthe managementgoal. Attempts
had been made to suppressbeetiepopulationson six of
the 10 study ,blocks'while four 'were left untreated.
Descriptions
of standcomposition,
elevationand habitat ty:peon thesestudyblocksarepresented
in Table 1.
Methods
One 4-square-mile,blockwas selectedfor sampling
within each study area. The shape of ,theblock varied
becauseof vegetationalirregularities.Fifty percent or
more of the treeswere to be lodgepolepine, a criterion
eThe infestation period for the mountain pine beetle in
lodgepole pine generally lasts about eight years. The period
begins when about one tree per.acre is infested, peaks when
approximately32 trees,peracre are under attack, and is about
to end when less than one tree per acre is infested.
JOURNAL OF FORESTRY
Table 1. Proportion of Trees 4 inches dbh and Larger on Blocks in the Teton-Targhee Area According to Elevation and Habitat
Type
Engel- Whitebark-
Block Name
Elevation
Habitat Lodg.
epole Douglas-Subalpine mann
type•
pine
fir
fir
spruce
limber
pines
Trees
Aspen
per acre
percent
No.
lnfestationconcluded
Treated
Pilgrim Mt.
6,900-7,700
A/P
86.7
2.7
7.6
1.4
1.6
0.0
311.0
Hatchet
7,000-7,800
A/P
90.9
6.9
0.2
0.7
0.0
1.3
274.5
Upper SpreadCreek
7,600-8,400
A/V
91.2
0.0
3.5
5.3
0.0
0.0
272.0
PacificCreek
7,200-8,400
TogwoteePass
8,700-9,300
Horseshoe-Packsaddle 6,600-6,900
A/V
A/V
A/P
79.0
41.9
64.1
0.0
0.0
14.3
16.8
14.5
15.0
3.3
20.1
0.4
0.9
23.5
0.0
0.0
0.0
6.2
288.5
236.0
233.5
Untreated
lnfestation continuing
Treated
SignalMt.
Warm River
Pineview
6,800-7,100
5,500-5,800
6,200
P/C
P/C
P/C
97.0
93.2
98.8
2.8
5.3
0.3
0.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1.5
0.9
304.5
271.5
286.0
6,000-6,500
A/P
95.7
3.2
0.4
0.7
0.0
0.0
278.5
Untreated
Pine Creek
XHabitat type: A/P = Abies/Pachistima;
A/V = Abies/Vaccinium;
P/C = Pseudotsuga/Calamagrostis.
Classifiedaccordingto
Roe and
Amman (1970).
Fig. 1. Snags indicate that many dominant lodgepole pine
trees have been killed by the mountain pine beetle. In spite
of losses, a large proportion of lodgepole pine trees have survived.
met on all ,blocksexceptone at high elevation.Twenty
fixed, circular, 1/10-acre plots within each block were
locatedin a grid patterndescribedby Cole and Amman
(3). One-tenth-acreopeningswere avoided.The elevation of each ,plot was recordedand the habitat type
deter.
mined by means of vegetational associations
definedby Roe (13).
Measurements
were recorded •or art trees that were 4
inches dbh or larger. Individual trees were fisted by
speciesand as.beingdeador alive. Dead lodgepolepine
trees were classifiedas having been k'filed by the
mountainpine beetle or by somecauseother than the
mountain pine beetle;i.e., other bark beetles (Ips and
Pityogenes), tree competition,or undeterminedcauses.
The basalarea of survivingtreesthat avere9 inches
dbh or larger was used to measurethe beetle'seffect on
the operabilityof a stand.The 9-inch ,basewas chosen
because it is the smartest merchantable
sawtimber
size
considered
in the loggingof lodgepolepine and because
trees that are 9 inches dbh, or more, are most com-
monly killed by the mountain pine beetle.
Results
and Discussion
From 62-90 percentof the lodgepolepinesthat had a
4-inch dbh or more and 32-92 percentof the merchantable basal area survived the mountain pine beetle
infestation.Survivalof smallrather than large-diameter
trees.wasproportionallygreaterin aU areas (Figs. 2
and 3). The six lodgepolepine standsin which infestation was completesustainedattack from four to nine
years. The other four standswere sti31irdested,even
though outbreaks had begun from four to 14 years
earlier (Table 2 ).
Percent survival and length of irdestfitionperiod in
both
treated
and untreated
.areas at •bout
the same
elevation •ere similar. Differencesbetween areas appear to be iar•gelyrelated to elevation.Control efforts
had slowed the rate of infestation in the two areas still
under attack, but evidencesuggeststhat the ilffestation
will continue until percent survival in treated areas
approximatesthat in untreated areas. Where beetle
infestationhad run its course,percentsurvivalof lodgepole pine indicatedthat control effortsusuallydid not
save trees.
APRIL
1972
205
Survival of Lodgepole Pine
The untreatedPacificCreek block had approximately
the samepercentsurvivalby individualdiameterclass
as the treated Pilgrim Mountain and Hatchet areas
(Fig. 2). Percentsurvivalof trees4 inchesdbh or more
ranged from 63-69 percent and that of merchantable
trees (9 inches dbh or more) from 36-42 percent
(Table 3).
Upper SpreadCreek, TogwoteePassand HorseshoePacksaddle, the other three blocks in which infestation
had ended, showed different survival curves (Fig. 2).
In Upper SpreadCreek, percentsurvivalof all lodgepole pines(4 inchesdbh. or more) was 74 percentand
the merchantable
.basalarea, 61 percent.Somechemical controland extensiveloggingof trees.mostsusceptible to attack or already infestedmay have reducedthe
potentialfor beetlepopulationbuildupand resultedin
greater survival in residual leave strips. Elevational
differences
may be important,as well.
Percent survival
beetlepopulationincreasedand, in 1969, 24 treesper
acre were infested.Survival of lodgepolestems4 inches
dbh, and larger, has been reducedto 76 percent and
survivalof the merchantablebasalarea to 46 percent-not unlike the Pilgrim Mountain, Hatchet and Pacific
Creek blocks. The large, current beetle population
indicatesthat additionalmortality can be expectedon
SignalMountainand that pine survivaleventuallywill
be comparableto that in other areas in which the
infestationperiodhasended.
The relativelyfavorablesurvivalof lodgepolepine in
the Pine Creek, Pineview and Warm River blocks
reflectsrecentinfestations(Fig. 3). Basal area survival
figuresare alsofavorable.However,afterthreeyearsof
Fig, 2. Lodgepolepine survivalcurvesfor studyareas in which
the mountain pine beetle infestation had ended. I • Togwatee Pass; 2 = Upper Spread Creek; 3 = Pilgrim Mauntain;
4 = Pacific Creek; 5 = Hatchet; and 6 • Horseshoe-Packsaddle.
of both stems and basal area was
higheston the untreatedTogwotte Pass block. This
increasedsurvivalis probablyattributableto elevationrelated climatic conditionsthat adverselyaffect the
beetle. a
9c
• ec
The Horseshoe-Packsaddle
area showsa slightlydifferent survivalpatternby diameterclass:the larger dbh
trees were reduced proportionallymore than in any
othersampledblock.Survivalfor trees4 inchesdbh and
over was 68 percent,which comparesfavorably with
areas mentioned above, but only 32 percent of the
merchantable basal area survived. Horseshoe-Packsaddle had the lowest elevation of blocks in which the
infestationperiodwas complete.
The remainingblocks supportcurrent infestations.
The SignalMountain block is of interestbecauseit is
still under attack after 14 years. The infestationwas
treatedduring 10 of theseyearsand the mortalityrate
slowed. However, when treatment was stopped, the
Research Work Unit 2201, unpublished data, U.S. Forest
Serv., lntmtn. Forest and Range Exp. Sta., Ogden, Utah.
Table
ioc
2. Periads af Mauntaln
Pine Beetle
Infestatlon
•. 7o
.• eo
13.
"'
õo
•
4o
I0
Start
I
I
I
I
I
I
I
I
I
[
õ
•
•
•
9
I0
II
I•
I•
14
I•
I•+
(l•t•$)
Fig. 3. Lodgepolepine survival curves far study areas where
and
Mountain.
IOC
Treatment
End Length Start
9C
End Length
I
InJbstation
concluded
Treated
\
I
D. RM.
Years
Block name
•_•'•
Untreated
the mauntain pine beetle infestation was current. I = Pineview; 2 = Warm River; 3 • Pine Creek; and 4 = Signal
Treatment
Infestation
Treated
.•:50 ----
•
Pilgrim Mt.
1960
1968
9
1961
1967
7
Hatchet
1960
1968
9
1962
1968
7
1961
1968
8
1965
1968
4
1961
1968
None
None
---
---
None
--
--
?c
Upper Spread
Creek
Untreated
Pacific Creek
TogwoteePass 1965
1968•
8
4
HorseshoePacksaddle
1968
8
1961
\
f 40
...I
Treoted
-•,
InJ•stationcontinuing
Signal Mt.
Warm River
Pineview
Untreated
Pine Creek
1956 Current
1965
1966
Current
Current
1966
Current
14
1957
1966
10
5
1966
Current
4
4
1967
Current
3
4
None
--
--
%
---- Un•reo•ed
Treated
IO
5
6
7
8
9
D.B.H.
I0
II
12
13
14
15
16+
(Inches)
• Subtle increase and decline in infestation was difficult to date.
The main infestationperiod was 1965-68.
206
JOURNALOF FORESTRY
Fig. 4. Harvesting of lodgepole pine in the Upper Spread
Creek area reduced residual stand susceptibility and consequently cut lossesta the mountain pine beetle.
infestation, the Pine Creek block has lower numbers of
percent in the Warm River stand. These differences
in that standwere discontinued
four yearsago, and the
beefie populationhas increasedsince. This buildup
suggests
that factorsbelievedto contributeto increases
in populations
still exist,e.g.,treeshavingthickphloem
and largediameter(1, 3).
After four yearsof beetleactivity,the low amountof
tree mortality on the Pineview block indicatesthat the
survivingtrees in the large diameter classesthan the
Pineview and War.m River stands after three and four
yearsof infestation,
.respectivelyß
Also,only 56 percent
of the ,basalarea in the Pine Creek block was alive,
compared to 92 percent i•nthe Pineview block and 77
probably indicate that the infestation rate on the
control effort has slowed the rate of infestation.
Pineviewand Warm River blockshasbeenslowedby
controlattemptsß
Ultimate survivalis yet to be deter-
percentof the stemsare still alive. Moreover, most tree
mortality was attributable to other insects (Ips or
mined.
Pityogenes) .
Duration
of Inf0stati0n
In areaswheremountainpinebeetlepopulations
had
subsided,
infestations
lastedeightto nine years.Togwotee Pass,where infestationlasted only four years,
was the singleexceptionß
Pilgrim Mountain, Hatchet
and Upper SpreadCreek standswere treated, but the
other three, Pacific Creek, Horseshoe-Packsaddleand
Togwotee Pass, were not--an indication that control
attempts did not slow the rate of in.festationin these
areas.
Control attempts in the Signal Mountain and
Pineviewstandsand in the Warm River block apparentlyhavereducedtherateof in.festation.
SignalMountainhasbeenunderattackfor 14 yearsß
Controlefforts
APRIL 1972
Over 90
The effectivenessof a chemical control project in
reducingmountainpine beetlepopulationsis related to
at least seven operational •actors: (1) steepnessof
terrain; (2) ease of access; (3) training of control
personnel; (4) experienceof control personnel; (5)
radius of treatment applicationaround the stand of
protectedtrees; (6) acreageinfested;and (7) initiation
of control
efforts while
infestation
is small.
Most
of
these factors ,were optimal within the Pineview area,
whichmayaccountfor the apparentsuccess
of control.
The effects of control on the Warm
River
infestation
rate are not as apparentas in the SignalMountain and
Pineviewblocks.However, the rate of tree mortality is
slightly less than that in the untreated Pine Creek
block.
207
Cost-benefitratios become an important consideration when treatmentperiodsextend over a number of
years. For example, on Signal Mountain in Grand
Teton National Park, the preservationof aesthetic
valueswould be of primary concern.However,in spite
of 10 yearsof controlwork (1956-1966), the mountain
pine beefiepopulationhas increasedagain and, more
than likely, the infestationwill proceeduntil the proportionalsurvivalby diameterclassis similar to that
observedin the Pilgrim Mountain, Pacific Creek and
Hatchetsamples.
Beetleactivityis almostcertainto
continueuntil mosttreesof thick phloemare killed. It
would appearthat attemptsto suppressbeetlepopulations in national parks or in other areaswhere timber
productsare not involved,are of little or no valueand
that the eventual survival of lodgepolepine will be
about the same whether
or not the stand is treated.
However, tree cover will persistbecausemany of the
smallerlodgepolepinessurviveand other tree species,
such as su.balpine fir and Douglas-fir, become more
abundantasthey succeedlodgepolepine (13).
lodgepolepine 9 inchesdbh and largeris apparentin
all sampledblocks where the beetle .populationhas
declined (Fig. 5) and seemsto accountfor much of the
differencenoted in lodgepolepine survival. Percent
survivalof lodgepolepine rangedfrom 37 percentin
the lowestblock (averageelevation,6,800 feet) to 74
percentin the highestblock (averageelevation,8,900
feet). A similarrelationship
holdsfor basalarea,which
rangedfrom 32 percentat the Iomestelevationto 71
percent at the highest. Elevation-relatedtemperature
differencesand their effectson beetle biologyprobably
are responsible.
Current studiesat the Intermountain
Forest and Range ExperimentStation at Ogden (see
footnote2) indicatethat at higher elevationsthe beetle
is out of its .rangefor optimaldevelopment.Its biological activitiesare poorly synchronizedwith seasonal
weather changes;so a two-year life cycle and low
brood-survivalirequentlyresult.
The effect of mixed speciesstands(lodgepolepine
was 42 percentof the stemsin the TogwoteePass
block) was also considered.However, Flint (5) ob-
thresholdand beforethe costof protectionexceedsthe
value of protectedvolume.Protection,to be justified,
mustbe for a predetermined
period of time so that the
servedno differencein lodgepolemortality in mixed
speciesstands.In addition,Roe and Amman (13)
pointed out that the beefie is the primary agent in
lodgepolepine removaland so providesfor succession
by other tree speciesin standsunaffectedby wildfires.
They foundthe beetleactivein standswherelodgepole
pinetotaledlessthan40 percentof the stems.
The relationship
betweenlodgepole
pinesurvivaland
volume at time of cuttingwill warrant treatment expen-
elevation existedwhether or not blocks,weretreated, an
ditures. As an example, if 50 ,percentsurvival of
lodgepolevolume,or merchantable
basalarea, is arbitrarily set as the level at whicha standcan no longerbe
loggedprofitably,then sufficient,basalarea remainsin
only two of the sampled,blockswhere the infestation
has ended. Both of these blocks the treated Upper
SpreadCreek and the untreatedTogwoteePass--are at
high elevations.Surviving,basalarea.was reducedto
less than 50 percentin the other four standswithin
eight •.onine yearsafter the start of infestation.
indicationthat the land managerprobablywould not
have to considerimmediateharvestingof standsabove
about 8,000 feet in elevation. These standswould be
relativelysafe from severedamageby the mountain
pinebeetle.
Differences
in lodgepole
pine survivalassociated
with
In stands such as Pineview and Warm River where
timber products are involved, a thorough economic
analysismay be helpfulto the land manager.It should
be emphasized
that protectedtimber shouldbe utilized
before the stand volume falls below
Elevational
a memhantable
Differences
The effect of elevationon proportionalsurvival of
elevation are consistent with the observations of Gibson
(6), who found greaterlodgepolesurvivalat the upper
ends of his strips, and with the .work of Roe and
Amman (13) in which threehabitat typesin lodgepole
pineforestsweredefined,whichgenerallyare relatedto
elevationbut varywith slopeandaspect.Risksof losing
lodgepolepine to the mountainpine beetlein the three
Table 3. LodgepolePine BasalArea (sq. ft./acre) Living and Dead on 10 Blocksin the Teton-TargheeArea for
Trees 9 inches dbh and Larger
Basal area
Killed by mountain
Blockname
Surviving
pinebeetle
Killed by
othercauses
sq.ft.
percent sq.ft.
In, stationconcluded
percent
Total
sq.ft.
percent
sq.ft.
PilgrimMt.
28
38.1
43
39
62.4
58.7
2
3.2
73
UpperSpreadCreek
54
60.7
29
33.3
5
6.0
88
PacificCreek
43
42.4
57
56.7
1
0.9
101
Togwotee
Pass
53
71.3
31.9
18
24.5
3
29
66.8
1
lnfestationcontinuing
4.2
26
45.6
30
14
3
22.0
5.4
54.0
<1
0.4
0.7
2.2
64
49
30
56.0
23
42.4
1
1.6
54
Treated
Hatchet
22
36.1
1
1.5
62
Untreated
Horseshoe-Packsaddle
14
1.3
74
44
Treated
SignalMt.
Warm River
Pineview
49
45
77.3
92.4
I
1
56
Untreated
Pine Creek
208
JOURNALOF FORESTRY
and pure standsto mountainpine beetle attacks.However, once a beetle irffestationis concluded, mixed
8O
o=Trees
• 70
A/
standswill havea highertotalresidualstockingdue to
x=Bosol
Areo •//- •1
o //
the presenceof otherspecies.
Conclusions
As a resultof thisstudy,the authorsrecommend:
ß That managementgoalsbe well definedahead of
beetlecontroldecisionsand that land usesbe thoroughly evaluated.When harvest opportunitiesare threatened, chemicalcontrolsthat might slow the rate of
infestationmay or may not withstand economicand
environmental
scrutiny.Where recreationalor aesthetic
considerations
are the only threatened•esourcevalues,
6o
o
o, 50
••••
%x•/•/•--Bosol
Areo
chemical
40
x /
,"• I
6,500
•
7,000
I
7,500
I
I
8,000
I
I
8,500
s
I
9,000
Elevotion (Feet)
Fig. 5. Survival of lodgepole pine 9 inches dbh, and larger,
from mountain pine beetle attack increased directly with
elevation. I = Togwotee Pass (untreated); 2 = Upper Spread
Creek (treated); 3 ---- Pacific Creek (untreated); 4 = Pilgrim
Mountain (treated); 5 ---- Hatchet (treated); and 6 ---- Horseshoe-Packsaddle
(untreated).
habitat typeswere lowestin the Abies lasiocarpa/Vacciniumscopariumassociation(high elevations),highest
in the A bies lasiocarpa/Pachistimamyrsinitesassociation (mid-elevations), and intermediatein the Pseudotsuga rnenziesii/Calarnagrostis rubescens association
(low elevations). Our data follow the same trend for
the Abies/Vaccinium and Abies/Pachistima associations. However, we did not have data from a block in
the Pseudotsuga/Calamagrostis
association,where the
infestationperiod had already ended. Basingrisk on
habitat type rather than elevationalonewould permit
consideration
of differencesin slope,aspectand latitude.
differencein susceptibility
of lodgepolepine in mixed
APRIL 1972
Tree
cover
harvest easier to fulfill.
Literature
Cited
1. AI•I•AN, GENE D. 1969. Mountain pine beetle emergence in
relation to depth of lodgepole pine bark. USDA Forest Serv.
Res. Note INT-96, 8 p.
2. BALCH, R. E. 1958. Control of forest insects. Ann. Rev. Entomol.
3:449-4•8.
3. COLE, .WAL?EEE., and GENE D. AI•II•AN. 1969. Mountain pine
beetle infestations in relation to lodgepole pine diameterS.
USDA Forest S6rv. Res. Note INT-95, 7 p.
4.
Flint (5) and Roe and Amman (13) also found no
is not reconunended.
festation, and would make the recommendation of
immediate
Mixed Species
Mixed speciescompositionhas been considereda
meansof reducingtimber lossesto many insects(2).
However,our data on the mountainpine beetledo not
supportthis supposition.Percentsurvival of lodgepole
pine was no greaterin the Horseshoe-Packsaddle
block
that contained36 percentotherspeciesthan in blocks
that had lessthan 10 percentotherspecies.About 68
percentof the lodgepole,pine stemssurvivedon the
Horseshoe-Packsaddle
block,but only32 percentof the
merchantable
.basalarealived.AlthoughTogwoteePass
containedthe highestproportionof other tree species
(58 percent),the increasedsurvivalof lodgepolepine
was attributedto the effectof climateon the biologyof
the mountain pine beetle. The proportion of other
specieswould have to be considerablymore than 36
percentin the alerational zone of optimal beetle developmentfor lodgepolepinein mixedspecies
,foreststo
be less susceptibleto mountainpine beetle damage.
treatment
will persistbecauseof lodgepolepine survival in the
smallerclassesand succession
by other tree species.
ß That a commerciallodgepolepine stand (having
many trees of large diameter and thick phloem) be
harvestedimmediatelyif a pine beetle in.festationis
observed.High elevationstands(over 8,000 feet) are
an exception.Harvesting removes the potential for
beefie epidemicsand the.need for chemicaltreatment.
If harvestingof an infestedstand of lodgepolepine is
attempted,it should be timely to prevent tree losses
from reachingthe point where the operationbecomes
economicallyunsound.
ß That creationof lodgepolepine blocksof different
agesand separationof blocksof similar age, a management alternativesuggestedby Roe and Amman (13),
would prevent large areas of ,pine from becoming
susceptible
simultaneously
to mountainpine beetlein-
CRAIGHEAD, F. C., J. M. MILLER, J. C. EVENDEN, and F. P.
KEEN. 193/. Control work against bark beetles in western
forests and an appraisal of its results. J. Forestry 29:100110/8.
5. FLINT, H. R. 1924. Various aspects of the insect problem in
the lodgepole pine region. U.S. Forest Serv. D-1 Appl. Forestry Notes
54, 4 p.
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209