2. Vegetation Types in Yosemite Valley Vegetation TypeHectares% Mixed Conifer95049 Meadow1478 Riparian20811 Black oak985 Live oak41021 Other1286

3. Yosemite Valley 1899

4. Yosemite Valley 1961

5. 1899 1961 18661961

6. Early to mid-1900s Tree felling for buildings, campgrounds, and bark beetle control

7. Stump creation and subsequent infection by Heterobasidion annosum

8. Ponderosa pineIncense cedar

10. Yosemite Lodge complex 1972 cabin crushed by tree with rotted roots since 1973 7 fatalities 19 serious injuries Over $1M property damage

11. Yosemite Lodge 1975 Root disease centers outlined

12. Yosemite Lodge 1997 Root disease centers outlined

14. Public safety

16. Disturbance in Yosemite Valley

17. Number of Gaps 0 5 10 15 20 0 600 120018002400 3000 3600 4200 48005400 6000 6600 7200 7800 84009000 Gap size (m 2 ) N = 70 Mean = 1007 m 2 Median = 459 m 2 Range = 81 - 8300 m 2

19. Heterobasidion annosum gaps all started at a stump or stumps They may continue to expand for about 30 years

20. 10 meters Sentinel Beach Gap size = 4200 m 2

21. Armillaria mellea infection center Infects all tree species Gap started at an infected black oak.

22. Ponderosa Pine killed by western pine beetle, Dendroctonus brevicomis

23. Heterobasidion annosum + Armillaria mellea gap

24. Many gaps with very little regeneration and have not closed in

25. Change in gap area 1972-1999

26. El Capitan Picnic Area 1972

27. El Capitan Picnic Area 1997

29. Yosemite Valley as it used to be?

30. Prescribed burn Yosemite Valley

31. Opportunities for restoration?

32. Pollution regulations

33. Pollen records suggest that conifers may have dominated Yosemite Valley prior to the Miwok

35. Lake Tahoe Basin

36. Old Growth Total coniferous forest = 48,620 ha 1998 area in old growth = ~2138 ha Percent in old growth = ~4 % Historic old growth area = 26,740 ha (estimated) Historic percent old growth = 55 % (estimated)

37. Changes in forest composition over 150 yrs White fir and incense cedar have doubled in importance Jeffrey pine has declined by 50 %

38. No wildland fire > 800 ha has occurred since 1908 Lake Tahoe fires Century in the 20th Century Between 1974 and 1996, there were only 9 fires > 4 ha Effective fire suppression and the high elevation environment (i.e., short fire season) have kept large fires to a minimum

39. Stand Characteristics Lake Tahoe Seral Old growth Stems/ha  20 cm dbh 536 324 n=14 n=17

40. Sierra San Pedro Martir, Baja, Mexico

41. Lake Tahoe Basin Sierra Nevada Peninsular and Baja Ranges Sierra San Pedro Martir, Baja Lat. 39 o Lat. 31 o 2200-2900 m elevation 65 cm annual ppt. 2000-2600 m elevation 50-100 cm annual ppt.

42. Tree Species Lower Montane Pinus jeffreyi, Abies concolor, Calocedrus decurrens, P. lambertiana Upper Montane Abies magnifica, A. concolor, Pinus contorta, P. monticola Subalpine Pinus albicaulis, P. contorta, P. monticola, Tsuga mertensiana, Abies magnifica,

43. Fire Return Intervals Lake Tahoe SSPM Lake Tahoe and Baja 12-55 years 13-52 years

44. Stand Characteristics Lake Tahoe and Baja Stems/ha  20 cm dbh Seral536 Old growth324 SSPM, Baja134 n=16 n=14 n=17

45. Distribution of live trees by size class I = 20-50 cm; II = 50.1-100 cm; III > 100.1 cm 0 10 20 30 40 50 60 70 80 90 % stems in each DBH size class Seral n=5009 Old growth n=3718 SSPM n=1528

46. Fir engraver beetle, Scolytus ventralis Heterobasidion annosum in fir stump

47. Bark Beetles and Conifer Hosts

48. Pathogens and Conifer Hosts

49. Mortality curves for mixed-conifer species 0 100 200 300 400 500 600 60646872768084889296 Year # dead trees Seral Old growth SSPM

50. Lake Tahoe Basin 1996

51. Distribution of dead trees by size class I = 20-50 cm; II = 50.1-100 cm; III > 100.1 cm 0 10 20 30 40 50 60 70 80 90 SeralOld growthSSPM % stems in each DBH size class

52. Changing role of pathogens and insects: Lake Tahoe: Pathogens and insects responsible for most mortality Baja: Pathogens and insects most important on older trees Fire mosst important om smaller trees

53. Future Threats To California Forests Catastrophic fire Air pollution Urbanization Introduced pests

54. Management Prescribed fire Thinning

55. Sequoia National Park

56. Annosus root disease in giant sequoia

57. Conclusions Human management of forests can change historical roles of pathogens and insects These role changes and their consequences may not become apparent for decades Current “restoration” activities (e.g., prescribed fire) generally do not take into account pathogens and insects Returning forest to historical stand densities and processes will not necessarily return pathogens and insects to historical roles