Insect infestation of fire-injured trees in the greater Yellowstone area

14 Pages·1991·0.8 MB·English

by  Amman, Gene D

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ft 77, 9
/2^2_United States
Department Insect Infestation of Fire-
of Agriculture
Forest Service Injured Trees in the
Intermountain
Research Station Greater Yellowstone Area
Research Note
INT-398
Gene Amman
September 1991 D. 1
CD
Kevin C. Ryan2 CO
m
33
m
-<
ABSTRACT
Survival ofconifers followingfire depends on the
type and degree ofinjuries sustained, initial tree
Permanentplots were established in the Greater vigor, and the postfire environment, including
YellowstoneArea (GYA)followingthe 1988fires to weather and insect and disease population dynam-
determine response ofbark beetles tofire-injured ics (Ryan 1982, 1990). As fire injuries increase, the
conifers. Within 2years (1989and 1990), 67percent probability oftree death increases. Numerous
ofthe Douglas-fir had been infested by bark beetles authors (compare Peterson 1985; Peterson and
(primarily the Douglas-firbeetle) and wood borers; Arbaugh 1986, 1989; Ryan 1990; Ryan and others
44percent ofthe lodgepolepine were infested (prima- 1988)have identified the proportion ofcrown killed
rily by thepine engraver);82percentofthe Engel- as thekeyinjury contributingto death ofmost
mann spruce were infested (mostly by spruce beetle); trees, butinjuries to bole cambium orroots orboth
and 71percent ofthe subalpinefir were infested may dominate in some cases (Ferguson and others
(mostly by wood borers). Bark beetle infestation 1960; Ryan and others 1988; Ryan and Reinhardt
usually occurred in trees having50percent ormore 1988). Resistance to cambium injury increases with
basalgirdling byfire. However, uninjuredDouglas- the square ofthebark thickness (compare Martin
firalso had 46percent ofthe trees infested in 1990. 1963; Peterson and Ryan 1986), which in turn
The largeproportion ofuninjuredDouglas-firthat increases approximately linearly with diameter
was infested byDouglas-firbeetle in 1990suggests (Ryan and Reinhardt 1988). Multiple injuries are
infestation will increase in unburnedportions ofthe common and increase the likelihood ofdeath
GYA. Ofthe trees that died, afire-injury model (Furniss 1965; Ryan 1990; Ryan and others 1988;
correctlypredicted deathforone-halfofthe Douglas- Wagener 1961). Mortality resultingfrom crown kill
firand two-thirds ofthe lodgepolepine, but all ofthe is often apparentby the end ofthefirst growing
Engelmann spruce and subalpinefir. season followingfire, while death resultingfrom
bole and rootinjury often does notbecome apparent
KEYWORDS: Pseudotsuga menziesii, Pinus before the second growing season (Ferguson and
contorta, Picea engelmannii,Abies others 1960; Ryan and others 1988; Ryan and
lasiocarpa, Dendroctonuspseudo- Frandsen 1991).
tsugae, Ipspini, Dendroctonus Barkbeetles and wood borers are frequently
rufipennis, Cerambycidae, associated with tree mortalityfollowingfire. How-
Buprestidae, Dendroctonus ever, itis difficultto adequately assess fire injuries,
ponderosae particularly to the bole and roots. In the absence of
significantbole or root injuries, the probability of
attack by primarybarkbeetles is initially low with
light defoliation, increases with moderate toheavy
defoliation, and often declines with complete defolia-
^ProjectLeader,MountainPineBeetlePopulationDynamics
researchworkunit,IntermountainResearchStation,Forest tion (Furniss 1965; Miller and Keen 1960; Mitchell
Service,U.S. DepartmentofAgriculture,locatedattheForestry and Martin 1980;Wagener 1961). Barkbeetles also
SciencesLaboratory, Ogden,UT. attack trees with cambium injurybut are thoughtto
^ResearchForester,IntermountainResearchStation,Forest contribute little to mortality, except in conjunction
Service,U.S. DepartmentofAgriculture, locatedattheInter- with defoliation or when alarge proportion ofthe
mountainFireSciencesLaboratory,Missoula,MT.
1
circumference is killed (Ferguson and others 1960; from species anddiameter and used as a measure
Ryan and Frandsen 1991; Wagener 1961). Second- ofresistance to cambium injury, to predictthe fate
arybarkbeetles (those commonly attracted to ofburnedtrees. Bevins (1980) modeledpostfire
severely weakened orrecentlykilled trees, as survival ofDouglas-fir 1 year afterburningusing
opposed to primarybarkbeetles that can infestand tree diameterand scorchheight as predictive
kill healthy trees) and wood borers are commonly variables.
attractedto burned trees, but their contribution to Although ourunderstandingoffire-causedmortal-
mortality, while thought tobe minor (Mitchell and ityhas improved and application modelshavebeen
Martin 1980), is largely unknown. developedforpredictingthe fate offire-scorched
Ryan and others (1988) reexamined conifers conifers in the Northern Rocky Mountains, the
8 years afterburningand demonstrated the impor- relationship ofinsects to fire injury is still notwell
tance ofbole injury in predicting survival. Percent- understood. In the aforementioned studies, insects
age crown scorch, degree ofcambium injury, and attackedtrees tovaryingdegrees, buttheir contri-
diameterwere the best predictors ofsurvival for bution to mortality andhost/insect species relation-
those trees. Wyant and others (1986) alsofound ships was not determined. The degree to which
thatpercentage ofcrown scorch and tree diameter fire-injured trees lead to abuildup ofpopulations
were the bestpredictors ofDouglas-fir survival. capable ofattackingnearby unburned trees also has
Peterson and Arbaugh (1986)found percentage notbeen determinedformost species. Therefore,
crown scorched and percentage basal circumference studies were started in the GreaterYellowstone
scorched were the bestpredictors oflodgepole pine Area (GYA) in 1989 followingthe large fires that
survival in the Northern Rocky Mountains. They occurred in 1988 to determine (1) rate ofbark beetle
showed crown scorch andthe level ofinsect attack infestation offire-injured trees; (2) change in infes-
were mostimportant as predictorsofsurvival of tation behaviorfromfire-injured to uninjured trees;
Douglas-fir. However, they did notidentify the and (3) barkbeetle and woodborerinfestation in
insects causingtree mortality. In contrast, Peterson relation to degree ofindividual tree injury.
andArbaugh (1989) observed thatinsect attack was Forestfires in the GreaterYellowstone Area
not a significant variable in predictingthe fate of (which consists ofYellowstone National Park and
fire-injured Douglas-fir in the Cascade Mountains, adjacentlands) severely charred millions oftrees,
possibly because insectpopulations were low. instantlykillingthem. Countless others were
Several recent studies have modeled postfire defoliated, girdled, orpartially girdled byheat
survival ofNorthern RockyMountain conifers. (fig. 1). Fire-killed and injured trees provide infes-
Ryan and Reinhardt (1988) modeledpostfire sur- tation opportunity to bark beetles and wood-boring
vival ofseven Northern RockyMountain conifer insects (Fellin 1980; Furniss and Carolin 1977)
species. They used percentage crown scorch as the when populations existin thevicinity ofthe fires.
only injury variable, andbarkthickness, calculated
2
Bark beetle surveys in the GYA suggestthat all
species were atlow population levels at the time of
the 1988 fires, with the exception ofthe Douglas-fir
beetle (Dendroctonuspseudotsugae Hopkins) (DFB).
The massive infestations ofmountain pinebeetle
(D. ponderosae Hopkins) (MPB) that covered over
965,000 acres in Yellowstone Park in 1982had
declined to only 310 acresby 1986 (Gibson and
Oakes 1987) and to no infested trees in 1987
(Gibson and Oakes 1988). In the nearby Bridger-
MPB
Teton National Forest, infestation declined
from 3,224 trees in 1987 to 890 trees in 1988
(Knapp and others 1988).
Although no survey estimates are availablefor
otherbark beetle species in Yellowstone Park, sur-
veys ofadjacent areas showed only the DFB was
increasing, whereas sprucebeetle (D. rufipennis
Kirby) (SB) infestation was light (Knapp and others
1988) and pine engraver dpspini Say) populations
had declined (Gibson and Oakes 1989).
METHODS
Canopy fires that caused complete defoliation
usually resulted in complete burningor severe
scorchingofthe innerbark, especially in thin-
barked species, so that trees with this type ofinjury
were no longer suitable forbark beetle infestation
(Amman in press). As a result, our sampling
focused on areas where canopyfires did not occur
and in adjacentunburnedforests. Observations
were made in GYAareas coveredbyfourfires
—
(fig. 2): (1) North Fork Fire—Bunsen—Peak and Figure 2 Study plot locations in Yellowstone
Madison River; (2) Snake River Fire GrantVillage; National Park and vicinity: (1) Bunsen Peak,
—
(3) Huck Fire Roc—kefeller Memorial Parkway; and (2) Madison River, (3) Grant Village, (4)
(4) the Hunter Fire Ditch Creek, about 35 miles Rockefeller Memorial Parkway, (5) Ditch
Creek.
south ofYellowstone Park. In each area, variable
plots (10 ft2/acre basal areafactor) were established
in 1989, with five additional plots establishedin
1990. Plots were mostly atlow elevations between measured as the percentage ofbasal circumference
6,725 and 8,000 feet; therefore, trees consisted in which the cambium was killed, and percentage
mostly oflodgepole pine and Douglas-fir. Trees crown scorch. Cambium injury was determinedby
were classified alive or dead, based on the presence removing small sections ofbark and visually inspec-
or absence oflivingfoliage and the percentage of tingtissues. Crown scorch was ocularly assessed
basal circumference girdledbyfire. Mortalityby and expressed as the percentage ofthe prefire
year (1988 to 1990) could still be determined in crown volume killed. Boringfrass expelled from the
1990. Individual trees within the plots were perma- bark was the usual sign ofinsect infestation. Some
nently marked in orderto follow survival for several bark was removedfrom trees infested by insects so
years, exceptin the heavily used Madison River
that insects couldbe identified. All insect observa-
area. Because ofthe possibility oftags being tions were made on the lower 7 feet ofthe trees.
removed by park visitors, successive observations Insects attackingtrees were classified accordingto
were made by comparingtree diameter and location whether they were primary or secondarybark
in the Madison River plots. beetles, woodborers, or other insects. The prelimi-
Observations included tree species, diameter at nary observations oftree mortality also were
breast height (d.b.h.), degree offire injury, presence compared to mortality predicted by the Ryan and
ofinsectattack, and insect species. Tree injury was Reinhardtmodel (1988).
3
RESULTS AND DISCUSSION on trees that are completelygirdled atthe base.
Given the slow rate ofdeath associated with basal
The small populations ofbarkbeetles in the GYA, girdlingand the currentlevel ofinsect activity,
coupled with timingofthe fires (July to September) additional mortality is expected. Dead trees were
in relation to life cycles ofbark- and wood-infesting somewhat (butnot significantly) smaller than live
beetles, resultedin nofire-injured trees in our trees (d.b.h. = 8.9 inches vs. 10.3 inches). Given the
samplebeinginfested in 1988. The SB, DFB, and extremely lowbark thickness to diameter ratio for
pine engraver emerge to infestnew material in the lodgepole (compare Ryan and Reinhardt 1988), itis
spring, priorto occurrence ofthe 1988 fires. The not surprisingthattree diameter was not signifi-
MPB emerges in late July and earlyAugust, butfew cantly differentbetween alive andfire-killed lodge-
GYA
were in the pole pine.
Insects infestingtrees in 1989 and 1990ranged The large number oftrees infested by pine en-
from the aggressiveDendroctonus (capable of graver was not surprisingbecause these beetles are
infestingandkillingtrees) to the nonaggressive able to reproduce in wind-broken material (includ-
wood borers (capable ofinfesting only severely inglargebranches) and in decadent trees near
weakened and dead trees) (table 1). death (Sartwell and others 1971). Mature forests
always seem tohave plenty ofsuch material avail-
able. Although not causingnoticeable tree mortal-
Lodgepole Pine
ity in 1988, the engraver waspresent in sufficient
Lodgepole pine (Pinus contorta var. latifolia numbers to infestmanyfire-injured lodgepole pine
Engelmann) isthe most abundant tree in the in the spring of1989.
samples. In 1989, 24 percent ofthe 147 lodgepole The mountain pine beetle was observed in only
were infestedby insects, increasingto 44 percentin seven trees, all in the Hunter Fire on the Bridger-
1990 (fig. 3). The pine engraver accountedfor most Teton National Forest. MPB was mixed with pine
ofthis infestation (71 percent ofinfestedtrees). Of engraver and the twigbeetle {Pityophthorous
the trees infested, only 5 percenthad notbeen confertus Say) in these trees, a common occurrence
scorchedbyfire. Most commonly, trees infested by when MPB populations are at alow level (Schmitz
the pine engraverhad greater than 80 percentbasal 1988).
MPB
girdlingbyfire (fig. 4). Many ofthese trees showed Observations overthe years suggest that is
little evidence ofscorch and looked healthy except not strongly attracted to fire-scorched trees, so few
forboringfrass made by the beetles. However, upon trees probably wouldhave been infested even if
closerinspection, the trees were completelygirdled larger populations ofMPB hadbeen present in the
GYA MPB
at thebase by a lightground fire. Based on the seldom breeds in trees injured orkilled
1990 survey data, 49 percent ofthe original trees byfire in numbers sufficient to cause an increase
(infested anduninfested) were classified dead in the population (Mitchell and Sartwell 1974).
(table 2). Observed mortality is abouttwo-thirds Hopkins (1905) found no MPB in fire-injured pon-
ofthat predictedby Ryan and Reinhardt (1988). It derosa pine in the Manitou Park area ofColorado.
often takes in excess of2years for all foliage to die Blackman (1931), workingon the Kaibab National
—
Table 1 Bark beetles and wood borers infesting trees in theGreaterYellowstoneAreafollowing the 1988 fires
Bark beetles
Host Primary Secondary Borers Other
Lodgepole pine Dendroctonusponderosae Ipspini Buprestidae Trypodendronsp.
Dendroctonus valens Cerambycidae Hylurgopssp.
Pityophthorusconfertus Hylastes sp.
Pityogenesknechteli
Douglas-fir Dendroctonuspseudotsugae Pseudohylesinussp. Buprestidae
Cerambycidae
Engelmann spruce Dendroctonusrufipennis Ipspilifrons Buprestidae Siricidae
Scierussp. Cerambycidae Trypodendronsp.
Subalpinefir Buprestidae
Cerambycidae
4
Lodgepole Pine (Pinus contorts) Lodgepole Pine (Pinus contorta)
1-20 21-40 41-60 61-80 81-100
Percent Basal Circumference Killed
— —
Figure3 Percentage of lodgepolepine Figure4 Percentage of lodgepole pine in-
infested primarily by Ipsp//7/'following the fested primarily by Ipspini'm relation to basal
Greater YellowstoneAreafires. circumference girdled byfire. Total numberof
trees intheclass appearson topof each bar.
—
Table 2 Numberof plots installed by year, speciesdistribution, total numberoftrees, proportion infested by insects, and
proportion killed byfire but uninfested
Tree species
Abieslaslocarpa Pinuscontorta Plceaengelmannil Pseudotsugamenziesii
Plots/year Killed, Killed, Killed, Killed,
Fire 1989 1990 Infested uninfested Infested uninfested Infested uninfested Infested uninfested
Number/proportion
North Fork 3 4 6/0.00 /0.00 95/0.49 /0.10
Snake 1 12/0.50 /0.00
Hunter 7 8/0.50 /0.50 54/0.58 /0.15 15/0.87 /0.00 4/0.25 /0.00
Huck 9 9/0.89 /0.11 75/0.36 10.00 2/0.50 /0.50 26/0.85 /0.04
Total 19 5 17/0.71 /0.29 147/0.44 /0.05 17/0.82 /0.06 125/0.67 /0.04
Forestin northern Arizona, found MPB were not on the plots. To date, 71 percent ofthe Douglas-fir
—
attractedto fire-scorched trees. He thought the (both infested and uninfested)have died over twice
scorched phloem did not offerfavorable conditions as many as predictedby Ryan and Reinhardt's
forbeetle offspring. Geiszler and others (1984) (1988) model. In thick-barked species, a strong
observedMPB mostly in trees uninjured orlightly negative relationship between diameter andmortal-
injuredbyfire, in contrastto pine engraverthat ity is normallyexpected in the absence ofsevere
occurred in moderately to heavilyinjured trees. crown scorch (Ryan and Reinhardt 1988; Ryan
Rust (1933) reported fire-injuredponderosa pine 1990). Contrary to expectation, dead trees were not
were infestedby MPB thefirstyearfollowingafire significantly smaller than those still alive. Apos-
in northern Idaho; however, the infestation declined sible explanation is that Douglas-fir tends to have
the nextyear. large lateralroots nearthe soil surface that are
The woodborers, both Buprestidae and Ceram- often injured by groundfires (Ryan and others
bycidae, were found occasionally in fire-injured 1988). Thus, unmeasured rootinjury mayhave
lodgepole pine. contributed to the higher-than-expected mortality.
However, because several ofthe dead Douglas-firs
Douglas-fir received minimal heating, insects appear to be
responsibleforpartofthe additional mortality.
Douglas-fir (Pseudotsugae menziesii [Mirb.] Ofthe 125 Douglas-fir examined, 26 percentwere
Franco) was the second most common tree found infestedby insects in 1989, mostly DFB (58 percent
5
ofinfested trees) and afew wood borer larvae of Oregon followingafire in 1933. Beetles subse-
both Buprestidae and Cerambycidae. Mostinfested quentlykilled large numbers ofuninjured trees in
Douglas-fir in 1989 had 50 percent ormore stem 1935 and 1936. Furniss thought DFB were able to
girdlingbyfire (Amman in press). In 1990, infested increasebecause frequentfires in the area provided
trees increased to 67 percent ofthe total (fig. 5), large numbers ofinjured trees for successive gen-
and most ofthese had 20 percent ormore stem erations, thus allowingthe beetles to increase.
girdling. In addition, the number ofuninjured trees
infestedby DFB increased dramatically in 1990,
Engelmann Spruce
when 46 percent ofthe 55 trees in this category
were infested (fig. 6). In 1989, some Douglas-firs Engelmann spruce (Picea engelmannii Parry)
thathad needles and limbs completelyburned were
constituted a small part ofour tree sample, with
infestedby DFB in the base where the bark was
only 17 trees examined. Currently, spruce mortality
thick enough to protectthe phloem from directfire —
is 88 percent close to that predictedby Ryan and
injury orfrom drying so excessively thatbeetles
Reinhardt(1988). As expectedfor a thin-barked
wDoFuBldinnfoetstceodnsmtorsutctofegtghegarlelmeariiensiinngilti.veIntr1e9e9s0o,n species, mortality did not varyby tree diameter.
Insects infested 65 percent ofthe trees in 1989,
the Madison Riverplots, even though many ofthese
trees would have survived the fire injury. DFB also fiensctreedassipnrgucteo,8S2Bpewracsenitni5n01p9e9r0ce(nfitg.of7)t.heOmf.thAellin-
infested many trees at this site that were not sub- infested spruce except one had 81 percent or
jected to fire injury, indicatingthat DFB increased
greaterbasal girdlingby fire. Observations of
populations in fire-injured trees and readily spread
spruce not on our plots showed the duffaround
to uninjured trees. Given the current level ofinsect
thebase resulted in a slow-burningfire that often
activity, additional Douglas-fir mortality is expected
burned offthe roots or so weakened them that some
in 1991.
trees were easilyblown overby wind. Windthrown
This appears tobe somewhat contrary to observa-
tionsby Malcolm Furniss (1965), whofound DFB spruce with unscorched trunks created an ideal
habitatforthe SB, which shows a strongpreference
infested 88 percent offire-injured Douglas-firfol-
for windthrown trees (Schmid and Hinds 1974).
lowing afire in Idaho, butbrood survival was low
The small additional infestation that occurred in
because ofpitch invasion ofgalleries and sour sap
condition. He did not report any infestation after 1990 is probablybecause the spruce beetle has a
2-year cycle in the area. Additional mortality is
t(h1e94f1i)rsotbpsoesrtvfierdeDyeFaBr.buHiolwdeuvpeirn,DRooubgelarst-Ffuirrniinss expected when beetles from trees infested in 1989
emerge in 1991.
Douglas-fir (Pseudotsuga menziesii) Douglas-fir (Pseudotsuga menziesii)
1988 1989 1990 1-20 21-40 41-60 61-80 81-100
Year Percent Basal Circumference Killed
— —
Figure 5 Percentage of Douglas-fir infested Figure 6 Percentage of Douglas-fir infested
primarily by Douglas-fir beetle following the primarily by Douglas-firbeetle in relation to
GreaterYellowstone Areafires. basal circumference girdled byfire. Total
numberoftrees in the class appears on top
of each bar.
6
Subalpine Fir the physiological responses offire-injured trees and
theirrelationships with insect ecology.
Subalpinefir (Abies lasiocarpa [Hook.] Nutt.) is Although our sample oftrees is small when the
noted for its lack offire resistance, primarilybe- total number oftrees in the GYAis considered,
cause ofits thin bark. Virtually anyfire vigorous these observations suggestan increasingtrend for
enough to burn on all sides ofthe tree will cause barkbeetle infestation ofboth fire-injured and
girdling, followed by sloughingofthe deadbark. All uninjured treesfor 1991 and probablybeyond.
17 subalpinefirs died followingthe fires. Ryan and Preliminary indications are that existingmodels for
Reinhardt's (1988) model accurately predicted the predictingfire-caused mortality ofthese species
fate ofthese trees. Wood borers (Buprestidae and should be used with caution followingwildfires,
Cerambycidae) infested 35 percent ofthe subalpine particularly in areas ofuneven burningnear the
fir in the sample in 1989 (fig. 8). Infestation in- edges ofmore severelyburned forests.
creased to 71 percent in 1990. All ofthe trees had
suffered 81 percent or greaterbasal girdlingbyfire;
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Year Year
— —
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