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document Historic, archived Do not assume content reflects current scientific knowledge, policies, or practices. Wood Bark Beetle and Borer Infestation in the Greater Yellowstone Area During Four Postfire Years Lynn A. Rasmussen Gene Amman D. James C. Vandygriff 2s trtC Robert D. Oakes A. Steven Munson > Kenneth E. Gibson ~? O s> TO cn -c The Authors Research Summary Lynn A. Rasmussen is Supervisory Technician, Extensive surveys ofbarkbeetle and wood borer infes- Mountain Pine Beetle Population Dynamics Research tation in the Greater Yellowstone Area were conducted Work Unit, Intermountain Research Station, located in 1991 through 1993. The study objectives were to atthe Forestry Sciences Laboratory, Logan, UT. determine the effect of delayed tree mortality following Gene D. Amman (retired) was Principal entomologist the 1988 fires on mosaics of fire-killed and green tree stands, the relationship between fire injury and subse- and Project Leader, Mountain Pine Beetle Population quent infestation, and the effect of insect buildup in fire- Dynamics Research Work Unit, Intermountain Research injuredtrees on infestation rates for uninjured trees. Station, located atthe Forestry Sciences Laboratory, Surveys were conducted adjacent to roads, and plots Ogden, UT. were selected randomly. In 1991, 321 plots were meas- James C. Vandygriff in Biological Technician, Mountain ured, 198 plots in 1992, and 127 plots in 1993. Insects Pine Beetle Population Dynamics Research Work Unit, killed 12.6 percent ofthe Douglas-fir (Pseudotsuga Intermountain Research Station, located at Forestry menziesii), 17.9 percent of the lodgepole pine (Pinus Sciences Laboratory, Logan, UT. contorta), 6.6 percent of the Engelmann spruce (Picea engelmannii), 7.5 percent of the subalpine fir {Abies Robert D. Oakes is Biological Technician, Forest Pest lasiocarpa), and 2.8 percentofthe whitebark pine (Pinus Management, Northern Region, Coeur d'Alene Field albicaulis). Delayed mortality attributed to fire injury ac- Office, Coeur d'Alene ID. counted for more mortality than insects. Both types of A. Steven Munson is Supervisory Entomologist, Forest mortality greatly altered the original fire-killed/green tree Pest Management, Intermountain Region, Ogden Field mosaicsthat were apparent immediately afterthe 1988 Office, Ogden, UT. fires. Insect infestation was strongly and positively cor- related with the percentofthe basal circumference ofthe Kenneth E. Gibson is Entomologist, Forest Pest Man- tree that was fire killed in all species, except in Engel- agement, Northern Region, Missoula, MT. mann spruce where infestation peaked in the middle fire-injury class. Infestation in Douglas-fir, lodgepole pine, and Engelmann spruce increased through 1992 then declined in 1993. Although it cannot be said with certainty that insects built up in fire-injured trees and then caused increased infestation of uninjured trees, the high level of infestation suggests this is the case. Intermountain Research Station 32425th Street Ogden, UT84401 Wood Bark Beetle and Borer Infestation in the Greater Yellowstone Area During Four Postfire Years Lynn A. Rasmussen Gene D. Amman James C. Vandygriff Robert D. Oakes A. Steven Munson Kenneth E. Gibson Survival ofconifers following fire depends on the in the GreaterYellowstoneArea, surveys for insect type and degree ofinjuries, initial treevigor, and the activity were conducted to obtain a larger sample on postfire environment, which includes the influence whichto investigate interactions between insects and ofinsects, diseases, and weather. As fire injury in- fire-injured trees. The objectives ofour studywere to creases, the probability ofdeath due to one or more determine delayed tree mortality attributed to fire ofthese causes also increases. injuryand barkbeetles and the effects on mosaics of Bark beetles ofthe family Scolytidae and wood fire-killed andgreen (live)trees, the relationship be- borers ofthe families Buprestidae and Cerambycidae tween fire injury and subsequent infestation bybark arefrequentlyassociatedwith tree mortality following beetles and wood borers, and the buildup ofbark fire. In the absence ofsignificantbole orrootinjuries, beetles in fire-injured trees and subsequent infesta- theprobabilityofattackbyprimarybarkbeetles(those tion ofuninjured trees. attracted to healthy trees) is low when fight defolia- tionbyfire occurs andthe probabilityusuallydeclines furtherwith complete defoliation(Furniss 1965; Miller Methods and Keen 1960; Mitchell and Martin 1980; Wagener 1961). Secondary barkbeetles (those commonly at- Extensive surveys forbarkbeetle activitywere con- tracted to severely weakened orrecentlykilled trees) ducted in 1991, 1992, and 1993. The surveys followed and wood borers are drawn to burned trees, buttheir roads inYellowstone Parkand RockefellerMemorial contribution to mortality, while thought to be minor Parkway (fig. 1); limited resources prevented a more (Mitchell and Martin 1980) is largely unknown. complete surveythatwould have included backcoun- Observations on permanent plots thatwere estab- tryand areas closertoroads. The plotlocations were lished in the GreaterYellowstone Area in 1989 and randomizedbyselectingrandomdistancestobedriven 1990 showed increased susceptibility ofinsect infes- down a road, flipping a coin to determine whether tation with increased fire injuryfor mosttree species. plot establishmentwould be on the left or right side However, trees thatwere completely defoliated by ofthe road, and selectingat random the distance the canopy fires that also resulted in complete burning plotwould be located from the road (40 to 100 m). or severe scorchingofthe inner bark, especially in To be used in our study, the plot must have con- thin-barked trees, were no longer suitable forbark tained some treeswithgreenfoliage. Canopyfiresthat beetle infestation (Amman 1991; Amman and Ryan caused complete defoliation usually resulted in com- 1991). Insect contribution to tree mortality is some- plete burning or severe scorching ofthe innerbark, times difficult to determine because ofnonobvious especiallyinthin-barked species. Treeswiththistype bole and root injuries byfire. These injuries resultin ofinjurywere no longer suitable forbarkbeetle infes- inaccurate mortalitypredictions from existingmodels tation(Amman 1991). Therefore, oursamplingfocused based on crown scorch alone (Ryan andAmman 1994). on areas where canopy fires had not occurred and on Because ofthe small number ofpermanent plots adjacentunburned forest. Ifthe trees inthe plotwere used to followtree mortalitypertainingto fire injury dead or faded, the location was moved to the next — Figure 1 Roadswhere plotswereestablished (dotted lines) in the GreaterYellowstoneArea. even chain distance. A 10 basal area factorvariable long since a tree had been killed by bark beetles: plot was installed at each location. All trees in the (1) tree killed in current year—foliage green, fresh plot were examined and classified alive or dead boring frass, larvae or adults present; (2) tree killed based on the presence or absence ofliving foliage, inpreviousyear—foliagebrightorange to straw color; the percentage ofbasal circumference girdled by (3)tree killed insecondyearpast—foliage dull orange fire, and insect infestation. The numbers ofplots and most retained; (4) tree killed in third yearpast- examined were 321 in 1991, 198 in 1992, and 127 foliage dull orange to gray and most lost. This dates in 1993. Plot placement in 1992 and 1993 was along trees back to 1988, the year ofthe fires and the year the same roads surveyed in 1991, but they became thatthere was little infestation (Amman 1991). As more widely spaced in succeedingyears. Low eleva- with Douglas-fir, some errors could occur. For exam- m tions between 2,040 and 2,485 delineated plot lo- ple, a tree with little foliage or on a dry site would cations; therefore, trees consisted mostly oflodge- fade faster than a tree with a large crown or on a pole pine and Douglas-fir. moist site. Tree observations included species, diameter at An intensive studyby Schmid (1976) shows that breast height (d.b.h.), degree offire injury, presence the problem offading in Engelmann spruce is more ofinsect attack, and insect species. Tree injury was complicated than in Douglas-fir and lodgepole pine. measured as the percentage ofbasal circumference Needlesusuallyturngreenish-yellow and fall approxi- in which the cambiumwas killed. Injuries attributed mately ayear after spruce beetles infest the tree. to fire effects included trees with 100 percent stem However, some trees remain green until the fall of girdled by fire, while trees thatwere not 100 percent the second year (Massey and Wygant 1954). Apar- girdledbut showed signs ofinfestation bybarkbeetles ticularly complicating factor is that branches of or wood borers had injuries attributed to insects. some infested trees develop new growth in the sum- Cambium injury was determined by removing small mer followingthe year ofinfestation (Schmid 1976). sections ofbark and visually inspectingtissues. Bor- The densityofattackingbeetles, and hence complete- ing frass expelled from the bark was the usual sign ness ofblue stain fungal inoculation, are considered ofinsectinfestation. Some barkwas removed sothat factors affecting rate ofneedle drying and dropping theinsects couldbe identified, and insectobservations in spruce (Schmid 1976). m were made onthe lower 2 ofthe trees. Insects were Becausetherewasnoadditionalinsect-causedmortal- classified accordingto whethertheywere primaryor itytallied in 1993, except for a small amount caused secondary barkbeetles, wood borers, orother insects. by Douglas-firbeetle, 1993 data will not be included The year in which a tree died was estimated from in the figures. Percent basal girdling was observed foliarcharacteristics. We estimatedyearofdeath only continuously and placed into classes, then data were forDouglas-fir and lodgepole pine because othertree subjected to weighted regression analyses, because species were present in such small numbers thatloss ofdiffering sample sizes, to show differences. by year would not be meaningful. For Douglas-fir, trees infested the year ofthe sur- vey had green foliage and fresh boring frass on the Results and Discussion bole ofthe tree; the previous year's trees had mostly red foliage with some needle loss occurring. Trees Fire injury and bark beetle infestation, not only of infested 2 years previously had some red needles re- fire-injured trees but also ofuninjured trees, resulted maining,butmostneedleshaddried and fallen. Trees in considerable change to mortality estimates and to infested 3 years previously essentiallyhad no needles the mosaics offire-killed and green treestandsfollow- remaining, and some ofthe finer twigs had fallen. ingthe 1988 fires. This method is not accurate in all cases because Bedard (1950) stated that Douglas-firvaries greatly Tree Mortality by Cause in the elapsed time between Douglas-firbeetle (Den- Douglas-firmortalityconsisted of31.7 percentofthe droctonuspseudotsugae Hopkins) infestation and 1,012 trees examined, with 18.5 percent attributed to foliage discoloration. Some trees maintain red foliage delayed effectoffire injury, 12.6 percent attributed to for ayear orlonger afterbeetles have emerged from them. An occasional tree may exhibit some fading in barkbeetle andwoodborerinfestation, and 0.6percent tahnedfamlalyfolbleowcionngfiinnfeedsttaotiaonf,ebwustciattmtearyedapbpreaanrchmeotstled tdhuaettwoeurneid1e0n0tipfeirecdenctaussteesm(gfiigr.dl2)e.dMboyrtfairleiwtyasinatttrreiebs- uted to fire effects. Those that were not 100 percent (Furniss 1959). In lodgepole pine we used the characteristics pre- girdled, butbecame infested by bark beetles or wood sented by Cole and Amman (1969) to estimate how borers, had mortality that was attributed to insects. 3 100 Douglas-fir However, eventhough they still had green foliage, (Pseudotsugamenziesii) green phloem, and appeared alive, almosttwo-thirds ofthelodgepolethatsubsequentlyfadedhadbeencom- 80 pletelygirdled bylight ground fires. Many ofthese trees' deaths from fire injurywere notapparenteven 3 to 4years afterthe fires, and quite often not until the lodgepole were infested bythe pine engraverdps pini [Say]) orthe twigbeetles,Pityophthorousconfer- tus Swaine andPityogenesknecteli Swaine, did rapid fadingoccur. Ofallthe lodgepole pine that died from all causes, includingfire injury, 44 percent were infested bythe pine engraver. Mountain pine beetle, Dendroctonusponderosae Hopkins, infested only 0.8 Green Fire Insect Unknownmortality percent ofthe lodgepole. StandComposition(present) Inthisdataset, andasobservedbyothers(Blackman Figure2—Alive (green) and dead Douglas-fir 1931; Hopkins 1905), mountain pine beetle is not bycause of mortality. strongly attracted to fire-injured trees. In addition to the stress offire injury, trees had been subjected to drought for several years. These stress factors did not significantly increase nor precipitate an out- Mostinfestation was bythe Douglas-firbeetle. Addi- break ofmountain pine beetles, which again points tional mortality, especially ofsmall diameter trees, to uniqueness in terms oflack ofresponse to stress was caused byPseudohylesinus nebulosus LeConte factors that are commonly associated with Douglas- and wood borers. firbeetle and pine engraver infestations. These data show that almost one-third ofthe Dou- Mortality ofEngelmann spruce totaled 41 percent glas-firthatwere green andconsidered alive following ofthe 439 trees in the sample: 31.9 percent were the 1988 fires died from delayed effects offire orin- killed by fire injury, 6.6 by insects, and 2.5 percent sectinfestation.Wheremortalityis evenly distributed, died from unidentified factors (fig. 4). Spruce beetle the fire-killed and green Douglas-fir mosaics appear (Dendroctonus rufipennis [Kirby]) killed almost one- slightly affected. However, where mortality is con- halfofthe spruce killed byinsects. Otherinsects that centrated, drastic altering ofthe mosaic is apparent. caused spruce death wereIpspilifrons Swaine and On the otherhand, lodgepole pine mortality con- wood borers offamilies Buprestidae and Cerambyci- sisted of51.6 percentofthe 4,758 sampledtrees. This dae. The high loss ofspruce to fire injury is related breaks down to 30.5 percent due to fire injury, 17.9 to thinbark, which causes them to be easilykilled percentduetoinsects, and 3.2 percenttounidentified by fire. causes (fig. 3). All trees retaininggreen foliage after Subalpine firhad 37.3 percent survival ofthe 134 the 1988firesmaybe considered survivors ofthe fires. trees in our sample. Most mortalitywas attributed Lodgepolepine (Pinuscontorta) .t—y-) Green Fire Insect Unknownmortality Green Fire Insect Unknownmortality StandComposition(present) StandComposition(present) — — Figure3 Alive (green) and dead lodgepole Figure4 Alive (green) and dead Engelmann pine by cause of mortality. spruce by cause of mortality. 4 100 Subalplnefir Whitebarkpine {Abieslasiocarpa) (Pinusalbicaulis) 80 20 20 Green Fire Insect Unknownmortality Green Fire Insect Unknownmortality StandComposition(present) StandComposition(present) — — Figure5 Alive (green) and dead subalpine fir Figure6 Alive (green) and dead whitebark bycause of mortality. pine by cause of mortality. to fire injury (50 percent), with insects accounting insects. Infestation ranged from a low of21.7 percent for only 7.5 percent and unidentified causes 5.2 per- in lodgepole with no injury to a high of66.6 percent cent(fig. 5). Subalpine fir is the most sensitive to fire in trees with 81 to 100 percent basal girdling by fire injury ofthe tree species in this study (Ryan and (fig. 7). The pine engraver accounted forthe most Amman 1994). Most insect-caused mortality ofsub- lodgepole pine infestation, rangingfrom 16.6 percent alpine fir was caused by wood borers in the families oftrees in the uninjured class to 44.8 percent oftrees Cerambycidae and Buprestidae. in the 81 to 100 percent basal injury class (fig. 8). Whitebark pine also appears sensitive to fire in- Twigbeetles (Pityphthorous andPityogenes) were jury in the fire types that occurred in the Greater the next most common, with the wood borers (Cer- Yellowstone Area in 1988, with only 36.1 percentof ambycidae and Buprestidae) infesting a few trees. the 144 trees in our sample surviving. Mortality in Regressions showingthe relationships ofinfestation trees was attributed tothe followingcauses: 59.7 per- to fire injury are given in figure 9. Infestation in- centto fire injury, 2.8 percentto insects, and 1.4 per- creased in all injury classes in 1992 (fig. 10). The centto unidentified causes (fig. 6). Whitebark pine increase in the uninjured class indicates a possible was usually killed by mountain pine beetle and pine jumpin pine engraverpopulations withinfire-injured engraver. trees in previous years resulting in the increase in Delayed mortality from fire injury and insects infestation ofuninjured trees. ranged between 41 and 64percentinthe tree species represented in this study. This mortalityresulted in drastic changes in dead and green tree mosaics that 100 Lodgepolepinedata1991,1992 were observed immediately followingthe 1988 fires. Losses to fire injury could be determined shortly afterthe fires by examining trees for complete basal fi 80 girdling; however, predicting losses to insect infesta- tionwas more difficult. Observations inthe nextsec- tion provide the basis formaking such predictions. Infestation in Relation to Fire Injury h Insect infestation was positively related to the percent ofthe basal circumference killed by fire in Douglas-fir, lodgepole pine, and Engelmann spruce. Meaningful relationships were not established for 1-20 21-40 41-60 61-80 81-100 Total subalpine fir and whitebarkpine because ofthe small PercentBasalCircumferenceKilled amount in our sample. — Our sample oflodgepole pine showed thata total of Figure7 Percentinsect infestation of lodgepole 43.9 percent ofall fire-injured trees were infested by pine byfire-injuryclass. 5 100 Lodgepolepinedata1891,1992 Lodgepolepinemortality1991versus1992 WeightedRegressionAnalysis > 1991 1992 5 8 Y= 14.0+0.32** a1991 V1992 V=27.2+0.21** uc> R"2=0.93 fl**2=0.80 US a c K 60 I 1 « 40 » 20 Cl 20 40 60 PercentBasalFireInjury 1-20 21-40 41-60 61-80 81-100 Total — PercentBasal CircumferenceKilled Figure 10 Relationship of insect infestation — to basal fire injury of lodgepole pine, 1991 Figure8 Relationship of pine engraver infes- versus 1992. tation to basal fire injury of lodgepole pine. Mountain pine beetle infested only a small number level, butbrood production was low which prevented oflodgepole pine and did not show much preference buildup ofthe beetle population. Not until mountain for any fire-injury class. Infestation ranged between pinebeetles infestbetterqualitylodgepole pine(those 0.3 percent ofthe trees in the 61 to 80 percent basal growing faster and having thicker phloem, which is injury class to 1.2 percent ofthe uninjured tree class the food ofdevelopinglarvae) does the population (fig. 11), which is consistent with previous measure- build to a potential outbreak. ments in the GreaterYellowstone Area (Amman Our sample ofDouglas-fir (1991 and 1992 surveys and Ryan 1991) and other studies (Blackman 1931; combined) showed that41.6 percent ofall fire-injured Hopkins 1905). Mountain pine beetle appears not trees were infested by insects. Infestation ranged to respond to trees stressed by fire or drought, since from alow of18.4 percent ofuninjured trees to a high both were present in the GreaterYellowstone Area of79.7 percent oftrees having 81 to 100 percent of duringthis study. An alternative hypothesis is that the basal circumference girdled by fire (fig. 12). The beetles respond to stressed trees but are unable to Douglas-firbeetle accounted forthe mostinfestation, build up populationsinthem. Schmitz(1988) observed rangingbetween 16.3 percent ofthe uninjured trees mountain pine beetle infesting diseased lodgepole to 47.0 percent oftreeshaving81 to 100 percentbasal pine when beetle populations were at an endemic Lodgepolepinemortality1991,1992 ,100 Lodgepolepinedata1991,1992 WeightedRegressionAnalysis V= 18.8+0.281*X 80 fl**2=0.94 60 40 20 1-20 21-40 41-60 61-80 81-100 Total 40 60 PercentBasalCircumferenceKilled PercentBasalFireInjury — — Figure 11 Relationship of mountain pine beetle Figure 9 Relationship of insect infestation infestation to basal fire injury of lodgepole pine, to basal fire injury of lodgepole pine. 1991 and 1992. 6