Vegetation Types in Yosemite Valley

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Vegetation Types in Yosemite Valley
Vegetation Type
Hectares

Mixed Conifer
950
49
Meadow
147
8
Riparian
208
11
Black oak
98
5
Live oak
410
21
Other
128
6
3
Yosemite Valley 1899
4
Yosemite Valley 1961
5
1899
1961
1866
1961
6
Early to mid-1900s
Tree felling for buildings, campgrounds, and bark
beetle control
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Stump creation and subsequent infection by
Heterobasidion annosum
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Ponderosa pine
Incense cedar
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Yosemite Lodge complex 1972 cabin crushed by
tree with rotted roots since 1973 7
fatalities 19 serious injuries Over 1M property
damage
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Yosemite Lodge 1975 Root disease centers
outlined
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Yosemite Lodge 1997 Root disease centers
outlined
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Public safety
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Disturbance in Yosemite Valley
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20
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Number of Gaps
10
5
0
0
600
1200
1800
2400
3600
4800
5400
6000
7200
7800
3000
4200
6600
8400
9000
Gap size (m2)
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Heterobasidion annosum gaps all started at a
stump or stumps They may continue to expand
for about 30 years
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Sentinel Beach
Gap size 4200 m2
10 meters
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Armillaria mellea infection center Infects all
tree species
Gap started at an infected black oak.
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Ponderosa Pine killed by western pine
beetle, Dendroctonus brevicomis
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Heterobasidion annosum Armillaria mellea gap
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Many gaps with very little regeneration and have
not closed in
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Change in gap area 1972-1999
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El Capitan Picnic Area 1972
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El Capitan Picnic Area 1997
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Yosemite Valley as it used to be?
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Prescribed burn Yosemite Valley
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Opportunities for restoration?
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Pollution regulations
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Pollen records suggest that conifers may have
dominated Yosemite Valley prior to the Miwok
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Lake Tahoe Basin
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Lake Tahoe Basin Old Growth
Total coniferous forest 48,620 ha
1998 area in old growth 2138 ha
Percent in old growth 4
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Changes in forest composition over 150 yrs
White fir and incense cedar have doubled in
importance
Jeffrey pine has declined by 50
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Lake Tahoe fires in the 20th Century
No wildland fire gt 800 ha has occurred since 1908
Between 1974 and 1996, there were only 9 fires gt
4 ha
Effective fire suppression and the high
elevation environment (i.e., short fire season)
have kept large fires to a minimum
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Stand Characteristics
Lake Tahoe
Stems/ha ? 20 cm dbh
Seral
536
n14
Old growth
324
n17
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Sierra San Pedro Martir, Baja, Mexico
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Lake Tahoe Basin
Lat. 39o
2000-2600 m elevation
50-100 cm annual ppt.
Sierra Nevada
Sierra San Pedro Martir, Baja
Lat. 31o
Peninsular and Baja Ranges
2200-2900 m elevation
65 cm annual ppt.
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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,
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Fire Return Intervals
Lake Tahoe and Baja
Lake Tahoe
12-55 years
SSPM
13-52 years
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Stand Characteristics
Lake Tahoe and Baja
Stems/ha ? 20 cm dbh
Seral
536
n14
Old growth
324
n17
SSPM, Baja
134
n16
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Distribution of live trees by size classI
20-50 cm II 50.1-100 cm III gt 100.1 cm
90
80
70
60
50
stems in each DBH size class
40
30
20
10
0
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Fir engraver beetle, Scolytus ventralis
Heterobasidion annosum in fir stump
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Bark Beetles and Conifer Hosts
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Pathogens and Conifer Hosts
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Mortality curves for mixed-conifer species
dead trees
60
64
68
72
76
80
84
88
92
96
Year
50
Lake Tahoe Basin 1996
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Distribution of dead trees by size classI
20-50 cm II 50.1-100 cm III gt 100.1 cm
90
80
70
60
50
stems in each DBH size class
40
30
20
10
0
Seral
Old growth
SSPM
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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
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Future Threats To California Forests
Catastrophic fire
Air pollution
Urbanization
Introduced pests
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Management
Prescribed fire
Thinning
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Sequoia National Park
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Annosus root disease in giant sequoia
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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