A mountain pine beetle outbreak developed on the north face of Shook Mountain in 1972. Beetle populations increased, and have continued at an epidemic level since 1973. Surveys show 404,798 ponderosa pine containing 12,173,940 bd. ft. volume of merchantable timber; and 20,875 lodgepole pine containing 730,625 bd. ft. volume of merchantable timber were killed from 1974 through 1976. Losses will continue as long as stands remain overstocked and stagnated. Reducing basal area below 120 ft. /acre by thinning and removing infested trees will manage the infestation. Suggestions are given to prevent buildup of secondary bark beetles

McGregor, Mark D.

United States. Forest Service. Northern Region. State & Private Forestry

Undetermined

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SD/i9(Aff3° FORE ST PPONG BINDE/aj, INSECT & DISEASEMANAGEMENTUSDA • FOREST SERVICE • NORTHERN REGIONState & Private Forestry • Missoula, MT 598015200Report No. 77-17	December 1977EVALUATION OF A MOUNTAIN PINE BEETLE INFESTATION,SHOOK MOUNTAIN, SULA DISTRICT,,BITTERROOT NATIONAL FOREST, 1977	 0is0) Fla41•'"M. D. McGregor	 4LL•62ABSTRACTA mountain pine beetle outbreak developed on the north face ofShook Mountain in 1972. Beetle populations increased, and havecontinued at an epidemic level since 1973. Surveys show 404,798ponderosa pine containing 12,173,940 bd. ft. volume ofmerchantable timber; and 20,875 lodgepole pine containing 730,625bd. ft. volume of merchantable timber were killed from 1974 through1976. Losses will continue as long as stands rylain overstockedand stagnated. Reducing basal area below 120 ft. /acre by thinningand removing infested trees will manage the infestation.Suggestions are given to prevent buildup of secondary barkbeetles.INTRODUCTIONA mountain pine beetle (Dendroctonus ponderosae Hopk.) outbreakdeveloped in second-growth ponderosa pine (Pinus ponderosa Laws)stands on the northeast side of Shook Mountain, Sula District,Bitterroot National Forest in 1972 (Hamel et al. 1974). Number ofinfested trees increased from 350 on 173 acres in 1972 to anestimated 1,200 trees on 624 acres in 1974, and over 100,000infested trees on 1,150 acres yearly through 1976. To obtain dataon infestation intensity and determine stand factors contributingto the infestation, a 1,150-acre area was surveyed in 1977 for barkbeetle damage.by2• ••IVSURVEY METHODSGreen, infested, dead tree, and volume loss estimates were obtained using avariable plot cruise (BAF=20). Plots were located at 5-chain intervals oncruise lines 5 chains apart within the infested area. All trees withinplots were recorded by species, diameter at breast height (d.b.h.), totalheight, and placed into the following classes:1 = green, uninfested2 = 1977 attack; green or partially faded, brood and blue stainpresent3 = 1976 attack; yellow foliage, brood emerged4 = 1975 or prior attack; majority of needles dropped5 = unsuccessful attack or pitchout; green foliage and pitchtubes;blue stain absent.Data were analyzed using the computer program INDIDS (Bousfield 1977).RESULTS Summaries of infested tree data are provided in table 1. Killed lodgepolepine averaged 7.6 inches d.b.h.; killed ponderosa pine averaged 8 inchesd.b.h. Remaining green trees averaged 8 inches d.b.h. for lodgepole pineand 9 inches d.b.h. for ponderosa pine.Table 1.--Estimated tree mortality and volume losses to mountain pinebeetle in second-growth ponderosa pine, Shook Mountain, Bitterroot National Forest, MT, 1974-1977Averaged.b.h.(inches)Treeskilledper acreTotal treeskilledVolumekilled/acre:(bd.	 ft.)Total volumekilled(bd.	 ft.)Year LPP PP LPP PP LPP PP LPP PP LPP PP1974 0 7 0 90.2 0 103,740 0 2,70E 0 3,142,2001975 9 8 2.2 89.6 2,549 103,040 77 2,68E 89,21f 3,091,2001976 7 7 2.5 92.3 2,822 105,222 87 2,769 98,770) 3,156,6601977 7 10 13.6 81.4 15,504 92,796 476 2,442 542,640 2,783,880Total or 20,875 404,798 730,625 12,173,940Average 7.6 8.0 6.1 88.3 . 213 2,65]LPP = Lodgepole pinePP = Ponderosa pine•••••••••••••0I e•Since 1972, the mountain pine beetle has killed 404,798 ponderosa pineamounting to a volume of 12,173,940 bd. ft. Since 1975, 20,875 lodgepolepine containing 730,625 bd. ft. have been killed.•Of the ponderosa pine killed, 26% were killed in 1974, 25% in 1975, 26% in1976, and 23% in 1977. Tree mortality occurred in 3- to 22-inch d.b.h. sizeclasses.Of trees killed, 71% were 0 - 4.9 inches d.b.h.; 43% were 5 - 11.9 inchesd.b.h.; and 27% were > 12 inches d.b.h. Approximately 63% of the stand from0 - 4.9 inches d.b.h.; 33% from 5 - 11.9 inches d.b.h.; and 12% of the trees> 12 inches d.b.h. has been killed.Percent mortality by diameter groups is shown in table 2.• Table 2.--Percent mortality/diameter classes, Shook Mountain, Sula District, Bitterroot National Forest, MT, 1975 - 1977 •Year 0 - 4.9 5 -	 11.9 12+1975 32 66 11976 32 66 11977 16 78 5Basal area (BA) ranged from 20 to 500 ft. 2/acre, averaging 184 ft.2/acre.Greatest BA was in the 5 - 11.9 inch d.b.h. classes, followed by the 0 - 4.9inch d.b.h. classes, with the least amount of BA in diameters > 12 inchesd.b.h.DISCUSSIONOutbreaks of mountain pine beetle in second-growth ponderosa pine stands arerelated to the following stand conditions (Sartwell and Stevens 1975):1.	 Species composition: pure or nearly pure ponderosa pine•Mortality (in percent)0	 d.b.h. Size Classes 410	(inches)•••••••••4 ••2. Stand structure: essentially even aged3. Stand age: 50 to 100 years4. Tree size: 8 to 12 inches d.b.h.5. Stand density: stem basal area generally in excess of 150ft. /acre.•In second-growth ponderosa pine, outbreaks develop almost exclusively instands which have been undisturbed for many years, and may develop duringyears of both normal and deficient precipitation (Beal 1943; Blackman 1931).Outbreaks occur earlier in stands on good sites than those on poor sites.For example, in central Oregon where much ponderosa pine rates as site classIII or IV (site index 71-98), stands usually sustain their first seriousinfestation between ages 50 and 75. In the Black Hills where site qualityis poor, generally class V or VI (site index 43-70) stands are usually 75 to100 years old when first infested (Meyer 1961).Overstocked ponderosa pine stands (BA > 150 ft. 2/acre) are generally moresusceptible to beetle attack (Sartwell 1971). The relationship of beetle-caused mortality to stand density is believed to be due to tree competitionwhich reduces vigor and allows beetles to kill a larger proportion of treesin a dense stand than in a sparse one. Since the greatest amount of BA iscontained in the 5 - 11.9 inch d.b.h. classes, thinning of trees with thesediameters would open stands and reduce competition. Griffin (1975) foundthat second-growth stands thinned below BA 120 ft. /acre sustained less treemortaliiy up to 4 years after thinning than stands thinned only to a BA of150 ft. /acre.Surveys in the Nine Mile drainage (McGregor et al. 1974) and data analyzedby Griffin (1975) show thinning affects stands in several ways: (1) beetlecaused tree mortality is significantly reduced; (2) spacing conditions areimproved with lower stand densities; and (3) uninfested portions of thinnedstands are unlikely to become infested in the future. Similar results havebeen reported for other stands in Oregon and Montana (Sartwell 1971;Sartwell and Stevens 1975; Stage 1958).RECOMMENDATIONS Silvicultural treatments deserve major emphasis in action programs againstmountain pine beetle in second-growth ponderosa pine stands. Direct controland most other insect-oriented approaches to pest management, althoughsometimes useful, are costly, difficult to apply over large areas, and oftenineffective.• •5Sales that remove infested trees, open stands, and leave mixed speciescomposition are encouraged. Basal area should be reduced below 120ft. /acre, with at least a 16-ft. spacing between residual trees. peyer(1961) Xisualized a site index 70 stand thinned at age 32 from 119 ft. BA to79 ft. BA. Subsequent intermediate cuts to 100 ft. BA, at 20-yearintervals, will minimize or prevent mountain pine beetle outbreaks. Such astand will reach a maximum of 134 ft. BA, at age 90, still below the 150ft. BA usually considered hazardous.Stands managed for other than maximum timber prfduction may be repeatedlycut to lower densities; for example, 80-ft. BA/acre. Under thereconditions, a stand greater than site index 70 will never exceed 98 ft. BA,well below hazard level.• Infested trees should be either salvage logged or skidded to a centrallanding and burned prior to beetle emergence. This will improve stand vigorand reduce and/or prevent future beetle infestation.IO	 Although there was a decline in number of infested ponderosa pine/acre from1976 to 1977, there was over a 6-fold increase in number of lodgepole pine• killed from 1976 to 1977. Management of mountain pine beetle in lodgepolestands has been described by Amman et al. (1977).Drought conditions during 1977 may weaken trees and make the ponderosa pinemore susceptible to attack by primary and secondary bark beetles in 1978.Ips plastographus (LeC.) and Ips pini (Say) were found infesting trees in• the Shook Mountain area. Both beetles can build to epidemic levels andcause significant tree mortality.Pine engraver beetles (Ips spp.) are frequently associated with loggingslash and thinning operations and prefer slash to standing green trees. Ifsufficient slash is not available to absorb emerging adult populations fromApril-September, beetles will attack groups of moisture-stressed trees.Damage to trees caused by Ips spp. can be minimized by: (1) providing aconstant supply of green slash from April through September, (2) thinninglarge areas by progressively thinning blocks of + 10 acres during summermonths, and (3) piling and burning slash as it becomes infested or whenI) thinning is completed. Avoid scorching standing trees when burning slash.Scorched trees are weakened and susceptible to attack by the red turpentinebeetle (Dendroctonus valens Lec.), as well as Ips spp. If weather preventsslash burning, chippers can be used to destroy beetle broods.Slash < 3 inches in diameter dries rapidly and produces few beetles. Slashexposed to direct sunlight dries rapidly and causes brood mortality.••••6 • •In logging and thinning areas, log decks can be left until they becomeinfested with Ips, then transported to the mill. These logs should beprocessed and the slash burned prior to beetle emergence to preventinfestation of adjacent forests.These practices will improve stand conditions and should reduce bark beetlepopulations to tolerable levels.•••••••0••0••1 W• •••••• ••••••REFERENCESAmman, Gene D., Mark D. McGregor, Donn B. Cahill, and William H. Klein.1977. Guidelines for reducing losses of lodgepole pine to mountainpine beetle in unmanaged stands in the Rocky Mountains. USDA ForestService General Technical Report INT-36, 19 pp. Intermountain Forestand Range Experiment Station, Ogden, Utah.Beal, J. A. 1943. Relation between tree growth and outbreaks of the BlackHills bettle. J. Forestry, 41:359-366.Blackman, M.W. 1931. The Black Hills beetle (Dendroctonus ponderosaeHopk.). New York State College Forestry Tech. Publ. 36. 97 pp.Bousfield, W. E. (In Press). Forest Insect and Disease Damage Survey.Griffin, D. N. 1975. Thinning ponderosa pine stand to reduce mountain pinebeetle-caused mortality on the Ninemile District, Lolo NationalForest. Special problem for master's thesis program. Washington StateUniv., Pullman, WA.Hamel, D. R., M. D. McGregor, and H. Meyer. 1974. Status of mountain pinebeetle on the Bitterroot National Forest, Montana and Idaho. USDAForest Service, State and Private Forestry, Missoula, Montana. Rept.No. 74-25.Meyer, W. H. 1961. Yield of even-aged stands of ponderosa pine. USDA Tech.Bull. 630 (rev.) 59 pp.McGregor, M. D., W. E. Bousfield, R. D. Lood, and H. E. Meyer. 1974.Mountain pine beetle impact survey Nine Mile drainage, Lolo NationalForest, and State and Private Lands, MT, USDA Forest Service, State andPrivate Forestry, Missoula, Montana.Sartwell, C. 1971. Thinning ponderosa pine to prevent outbreaks ofmountain pine beetle. From proceed. on Precommerical Thinning ofCoastal and Intermountain Forests in the Pacific Northwest atWashington State Univ., Pullman, WA.Sartwell, C., and R. E. Stevens. 1975. Mountain pine beetle in ponderosapine--prospects for silviculture control in second-growth stands.Jour. Forestry, pp. 136-140.Stage, A. R. 1958. Growth of thinned ponderosa pine in western Montana.Jour. Forestry, 54:757-760.

Evaluation of a mountain pine beetle infestation, Shook Mountain, Sula District, Bitterroot National Forest, 1977

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Evaluation of a mountain pine beetle infestation, Shook Mountain, Sula District, Bitterroot National Forest, 1977

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