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Recovery and Mortality of White Fir following the Douglas-fir Tussock Moth Bear Mountain Outbreak (2005-2007)

This study examines the recovery and mortality of white fir trees in Siskiyou County, CA, following a 3-year outbreak of the Douglas-fir Tussock Moth. The outbreak resulted in significant defoliation and top kill, with varying levels of damage across the landscape. Natural enemies played a crucial role in controlling the population. The study provides insights for targeted control measures during the peak phase to prevent damage and mitigate mortality.

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Recovery and Mortality of White Fir following the Douglas-fir Tussock Moth Bear Mountain Outbreak (2005-2007)

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  1. White fir Recovery and Mortalityfollowing theDouglas-fir Tussock Moth Bear Mountain Outbreak (2005-2007)Siskiyou County, CA2 - 4 years post outbreakDonald R. Owen

  2. Background information on DFTM, Orgyiapsuedotsugata • White fir is the principal host in CA and SW US • Douglas-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

  3. 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

  4. 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 2007 In 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

  5. Defoliation as mapped from aerial survey in 2006 Peak Phase of the Bear Mountain Outbreak Expansion of the outbreak in 2007 was due to mostly light defoliation in surrounding areas Outbreak centered on Bear Mountain and north of Sheepheaven Butte

  6. Photo pt 10 WF Recovery – Bear Mtn DFTM Outbreak 2009 2007 Light defoliation 2011

  7. Photo pt 13 WF Recovery – Bear Mtn DFTM Outbreak 5-20 % defoliation 2007 2009 2011

  8. Photo pt 13 WF Recovery – Bear Mtn DFTM Outbreak 5-20 % defoliation 2007 2007 2009 2011

  9. Photo pt 12 WF Recovery – Bear Mtn DFTM Outbreak 2007 20 % defoliation 2009 2011

  10. Photo pt 12 WF Recovery – Bear Mtn DFTM Outbreak 2007 20 % defoliation 2009 2011

  11. Photo pt 20 WF Recovery – Bear Mtn DFTM Outbreak 25-55 % defoliation 2009 2007 2011

  12. Photo pt 20 WF Recovery – Bear Mtn DFTM Outbreak 2009 2007 2011 25 % defoliation

  13. Photo pt 20 WF Recovery – Bear Mtn DFTM Outbreak 2007 2009 55 % defoliation 2011

  14. Photo pt 05 WF Recovery – Bear Mtn DFTM Outbreak 25 - 30 % defoliation 2007 2011 2009

  15. Photo pt 05 WF Recovery – Bear Mtn DFTM Outbreak 25 - 30 % defoliation 2007 2007 2011 2009

  16. Photo pt 07 WF Recovery – Bear Mtn DFTM Outbreak 33 % defoliation 2007 2011 2009

  17. Photo pt 07 WF Recovery – Bear Mtn DFTM Outbreak 33 % defoliation 2007 2009 2011

  18. Photo pt 02 WF Recovery – Bear Mtn DFTM Outbreak 2007 40 % defoliation 2011 2009

  19. Photo pt 02 WF Recovery – Bear Mtn DFTM Outbreak 2007 40 % defoliation 2011 2009

  20. Photo pt 14 WF Recovery – Bear Mtn DFTM Outbreak 50 % defoliation 2009 2007 2011

  21. Photo pt 14 WF Recovery – Bear Mtn DFTM Outbreak 2009 2007 50 % defoliation 2011

  22. Photo pt 17 WF Recovery – Bear Mtn DFTM Outbreak 55 % defoliation 2011 2009 2007

  23. Photo pt 17 WF Recovery – Bear Mtn DFTM Outbreak 2007 55 % defoliation 2009 2011

  24. Photo pt 03 WF Recovery – Bear Mtn DFTM Outbreak 2007 2011 60 % defoliation 2009

  25. Photo pt 03 WF Recovery – Bear Mtn DFTM Outbreak 2009 2007 60 % defoliation 2011

  26. Photo pt 06 WF Recovery – Bear Mtn DFTM Outbreak 70 - 30 % defoliation 2007 2011 2009

  27. Photo pt 06 WF Recovery – Bear Mtn DFTM Outbreak 70 - 30 % defoliation 2007 2009 2011

  28. Photo pt 11 WF Recovery – Bear Mtn DFTM Outbreak 2007 60 % defoliation 2009 2011

  29. Photo pt 11 WF Recovery – Bear Mtn DFTM Outbreak 60 % defoliation 2009 2007 2011

  30. Photo pt 19 WF Recovery – Bear Mtn DFTM Outbreak 2007 2009 60 % defoliation 2011

  31. Photo pt 19 WF Recovery – Bear Mtn DFTM Outbreak 2009 2007 60 % defoliation 2011

  32. Photo pt 04 WF Mortality – Bear Mtn DFTM Outbreak 2009 (dead 2008) 2007 85 % defoliation

  33. Photo pt 01 WF Mortality – Bear Mountain DFTM Outbreak 2009 (dead 2008) 90 % defoliation 2007

  34. Photo pt 16 WF Mortality– Bear Mtn DFTM Outbreak 95 % defoliation 2009 (dead 2008) 2007

  35. Photo pt 18 WF Mortality– Bear Mtn DFTM Outbreak 95 % defoliation 2009 (dead 2008) 2007

  36. Photo pt 08 WF Mortality– Bear Mtn DFTM Outbreak Ponderosa pine 2009 (white fir dead 2008) WF 90-100 % defoliation 2007 2011

  37. Photo pt 08 Ponderosa Pine Recovery – Bear Mtn DFTM Outbreak 2007 2009 2011

  38. Photo pt 15 Douglas-fir Recovery – Bear Mtn DFTM Outbreak 1-30 % defoliation 2011 2007 2009

  39. Photo pt 15 DF Recovery – Bear Mtn DFTM Outbreak 1-30 % defoliation 2007 2007 2009 2011 Douglas-fir

  40. ReferencesBeckwith, 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, Orgyiapsuedotsugata(McDunnough)(Lepidoptera:Lymantriidae). Mem. Ent. Soc. Can. 146:107-21Torgersen, 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.

  41. References continuedWickman, 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.

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