White fir White fir Recovery and Mortality Recovery and Mortality following the following the Douglas-fir Tussock Moth Douglas-fir Tussock Moth Bear Mountain Outbreak Bear Mountain Outbreak (2005-2007) (2005-2007) Siskiyou County, CA Siskiyou County, CA 2 - 4 years post outbreak 2 - 4 years post outbreak Donald R. Owen
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Background information on DFTM, Orgyia psuedotsugata
White fir Recovery and Mortality following the Douglas-fir Tussock Moth Bear Mountain Outbreak (2005-2007) Siskiyou County, CA 2 - 4 years post outbreak Donald R. Owen. Background information on DFTM, Orgyia psuedotsugata White fir is the principal host in CA and SW US - PowerPoint PPT Presentation
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White firWhite fir Recovery and Mortality Recovery and Mortality
(2005-2007)(2005-2007)Siskiyou County, CASiskiyou County, CA
2 - 4 years post outbreak2 - 4 years post outbreak
Donald R. Owen
Background information on DFTM, Orgyia psuedotsugata
•White fir is the principal host in CA and SW USDouglas-fir and grand fir are principal hosts elsewhere
•One year life cycle with egg hatch in June and pupation in July•5-6 instars typical•1st 3 instars account for 10% of defoliation•Last instar accounts for > 60% of the defoliation•Outbreaks are cyclic with a 7-10 year return interval
Outbreaks may last 1-4 years•In order to cause significant damage, an outbreak would typically go through 3 phases, each phase corresponding to one DFTM generation (one year)
• Release – rapid population increase; little, if any, noticeable defoliation
• Peak – highest population and most severe defoliation; natural enemies begin to exert control by the end of the generation
• Decline / Collapse – population initially high, but natural enemies cause population collapse; defoliation may be more widespread, but less severe
Damage
•Damage = top kill, mortality, and growth loss•Defoliation is measured as the % of crown completely defoliated•90% of mortality occurs in trees with > 90% defoliation•Trees with < 50% defoliation rarely die•Top-kill follows a similar trend•Defoliation varies significantly across the landscape, with heavy defoliation occurring in hotspots up to 50 acres in size•Hotspots typically occur on ridges, upper slopes, and poorer sites•To prevent damage, control should target the Peak Phase and concentrate on predicted hot spots•Control during the Decline Phase may reduce defoliation that year, but may have negligible effect on top kill and mortality•Overall, stands experience growth loss initially, but long-term effect is usually neutral or positive
Bear Mountain DFTM Outbreak
2005 No early detection monitoring in this area; population release occurs without notice
2006 Peak phase; high egg mass counts in some locations in the fall, but parasites and dead DFTM larvae and pupae are common; egg masses are relatively small and there is a low ratio of egg masses to pupal cases; 2,455 acres of defoliation
2007In hotspots, some trees or tops of trees do not break bud (mortality and top kill); DFTM population is initially high, but shows noticeable decline by 3rd instar in areas with the heaviest defoliation; parasites abundant; no egg masses could be found in the fall (population collapse); 7,444 acres of defoliation. This outbreak followed the typical 3-yr sequence of population release, peak, and decline
Defoliation
as mapped from aerial survey
in 2006
Peak Phase of the
Bear Mountain Outbreak
Outbreak centered on Bear Mountain and north of Sheepheaven Butte
Expansion of the outbreak in 2007
was due to mostly light defoliation in surrounding areas
References Beckwith, RC. 1978. In: The Douglas-fir Tussock Moth: A Synthesis. MH Brookes, RW Stark, and RW Campbell, eds. USDA For. Serv. Tech. Bull. No. 1585. p 66. Mason, RR and RF Luck. 1978. In: The Douglas-fir Tussock Moth: A Synthesis. MH Brookes, RW Stark, and RW Campbell, eds. USDA For. Serv. Tech. Bull. No. 1585. p 40 & 44. Mason, RR and JW Baxter. 1970. Food preference in a natural population of the Douglas-fir tussock moth. J. Econ. Entomol. 63(4):1257-9. Shepard, RF, DD Bennett, JW Dale, S Tunnock, RE Dolph, and RW Their. 1988. Evidence of synchronized cycles in outbreak patterns of Douglas-fir tussock moth, Orgyia psuedotsugata (McDunnough)(Lepidoptera:Lymantriidae). Mem. Ent. Soc. Can. 146:107-21 Torgersen, TR and DL Dahlsten. 1978. In: The Douglas-fir Tussock Moth: A Synthesis. MH Brookes, RW Stark, and RW Campbell, eds. USDA For. Serv. Tech. Bull. No. 1585. p 47-53. Wickman, BE. 1963. Mortality and growth reduction of white fir following defoliation by the Douglas-fir tussock moth. USDA For. Serv. Res. Pap. PSW-7. 14p. Wickman, BE. 1978. A case study of a Douglas-fir tussock moth outbreak and stand conditions 10 years later. USDA For. Serv. Res. Pap. PNW-244. 22p.
References continued
Wickman, BE. 1979. Douglas-fir tussock moth handbook. How to estimate defoliation and predict tree damage. Ag. Hdbk No. 550. 15p. Wickman, BE. 1980. Increased growth of white fir after a Douglas-fir tussock moth outbreak. J. For. 78:31-33. Wickman, BE. 1986. Growth of white fir after Douglas-fir tussock moth outbreaks: long-term records in the Sierra Nevada. USDA For. Sev. Res. Note PNW-440. 8p. Wickman, BE. 1988. Tree growth in thinned and unthinned white fir stands 20 years after a Douglas-fir tussock moth outbreak. USDA For. Sev. Res. Note PNW-RN-477. 11p. Wickman, BE.1990. Mammoth Lakes revisited – 50 years after a Douglas-fir tussock moth outbreak. USDA For. Sev. Res. Note PNW-RN-498. 6p. Wickman, BE, RR Mason, and CG Thompson. 1973. Major outbreaks of Douglas-fir tussock moth in Oregon and California. USDA For. Serv. Gen. Tech. Rep. PNW-5. 18p.
Williams, CB Jr, JM Wenz, DL Dahlsten, and NX Norick. 1979. Relation of forest site and stand characteristics to Douglas-fir tussock moth (Lep. Lymantriidae) outbreaks in California. Bull. Soc. Entom. Suisse. 52:297-307.