Sierra Nevada

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Transcript Sierra Nevada

Sierra Nevada
Sierras
• 400 miles
long
• 50 mile
wide
• Eastern
ridge of the
Central
Valley
• Many peaks
above
13,000 ft.
• Most of land
in National
Forest
Climate
• Strong rain shadow
– Higher Eastern side ( Nevada) drier
• Biotic Zonation of forest types
follows rain and temps.
• West Wetter in Sierra at 5500 ft:
– West Slope (Yosemite Valley Floor) 75"
– East Slope only 20"
Precipitation: North- South
• 300 miles north latitude is roughly
equivalent to 1,000 ft. gain in elevation.
– Timberline is 1,000 lower in north than south
• Average annual precipitation at 5000 ft
elevation:
– Wetter in North- 90 inches
– mid: Yosemite – 55 inches
– South: Kern County 30 inches
• Maximum Precipitation at 8,000 - 9,000'
– less Rain/Snow higher up.
• More than 50% of precipitation falls
between January to March
– less than 3% in summer
Growing season
• Varies by from 4 to 7 months
– Shorter the as you increase in latitude,
elevation.
• Alpine (felfield) has only 4-6 weeks
growing season in summer.
• At lower elevations (below snow line)
growth is limited by summer drought.
– especially on east Slope into desert.
Snow line
• Some snow lower down, but at snow line it
accumulates instead of quickly melting.
• Shift from winter growing season (wet) to
a summer growing season, at around
3,000 ft.
• Snow releases water slowly.
• Snow insulates with trapped air pockets
the vegetation beneath. Above blasted by
ice, cold winds
• 10 inches of snow = 1 inch of rain
Precipitation
• 8-10 inches of increased rain/snow
per 1,000 ft. gain in elevation at same
latitude.
• Some summer thunder showers
relieve drought a bit.
– But doesn’t add much over-all water
• Much less precipitation below 3,000
because of Rainshadow from Coast
Ranges.
Air Temperature
• At night and in winter, typically a
drop of 3°- 5° per 1,000 ft. gain in
elevation at same latitude.
High Elevations
• Air is drier at higher temps.
• Temperatures changes rapidly,
no moderating water vapor.
• Wind moves with great speed
over peaks
•Wind shearing, kills / blasts one side of trees.
–causes drying, chilling and abrasion to plants/animals.
•More intense uv light radiation
•Coarser, drier, more acidic soils
Eastern Slope
• Sagebrush
Scrub
• Desert
Summer Thermals
• Rising summer thermals over Great Basin
pull air over Sierra.
• Air pulled up slope air forms summer
thunder showers (adiabatic cooling).
• Causes Chimney effect as winds increase
as they are funneled up upper more
narrow canyons.
– dangerous for fire conditions.
• Also pull rising air from Great Central
Valley, pulls in from coast and get coastal
Summer FOG.
• Smog from coast, valley pulled up into
Sierras.
• Cooling air (denser air) at night
drops back down into valleys in
Sierras and into Great Central Valley.
• Created thermal inversion next day
until pull releases pressure.
Soil: Edaphic Properties
• Edaphic (soil) properties, combined with
slope determine plant communties
• Reddish laterite soils very nutrient poor
and may be acidic.
– brush and chaparral communities dominate on
laterite soils at lower elevations in foothills.
• Sandstone terraces uplifted from marine
bottoms.
• Serpentine soils are difficult for plant
roots, many endemic species live here.
Biotic Zonation
• Biotic zonation the General
progression, microclimate may allow
for over lap between zones for quite
a distance
Biotic Zonation of Sierras
Great Central Valley
• Great Central Valley floor - flood plains
with rich soil. 0- 400 ft. elevation
• Rain Shadow of Coastal ranges, some
areas average 10 inches of rain.
• Soil drains too quickly to support trees,
only along water ways (Riparian)
• Grasslands can reach up to 1,000 ft into
the foothills
Western Sierra Foothills
• Foothill phases reach up to 1,000 3,000 ft. depending on soil, etc.
• On rolling hills and plains, has
incredible spring wild flowers and
green grasses throughout.
• Valley Oak on Valley floor and riparian
corridors
Sierra Foothills continued:
• Blue oak- drier areas, upland.
– Deep roots and waxy drought-adapted leaves.
– Most palatable of acorns in California
• Interior live oak –
– higher elevations, just below coniferous forest
• Foothill (Digger) Pine also found mixed in
these areas.
– Long 7-13" needles in fassicles of three.
– large open cones
– round open crowns, multiple trunks
Valley Oaks – 400 ft.
Blue Oak
Sierra Foothills continued:
• North slopes - mixed evergreen forest
species:
– holly-leaf cherry, buckeye, bay, toyon, interior
live oaks, redbud
– scattered Foothill pines or Black oak at higher
elevations
• South slopes: Warm Chaparral
– impoverished soils
– mostly tough evergreen leaves covered with
resinous oils or waxes not drought deciduous.
– Chamise, Ceanothus, Yerba Santa
Buck brush Ceanothus
Chamise
Yerba Santa
Warm Chaparral
Yellow Pine Zone
• Yellow (Ponderosa and Jeffery) Pines
– 1,000 - 6,000 includes Yosemite Valley
– Ponderosa dominant along with White fir /
Douglas fir mixed conifer forest. Sugar pine
on upper reaches. Giant sequoia locally
important, in wetter zones.
• Average of 50 inches rain per year.
– Yosemite Valley Floor - 4,000' White fir also has
Douglas fir, and along stream course Red
Alder, White alder, Dogwood, Big leaf maple,
Yellow Pine Belt
• Valley floors have beautiful Black
Oaks, and Canyon Live Oak along
(AKA: maul / gold cup) canyon walls.
• Understory: Manzanita, Gooseberry currant, berries, Ceanothus.
– Also: Mountain Misery and Pinemat
(dwarf ceanothus).
– Spice bush, chokecherry, chinquapin
Giant Sequoia
• Moister sites in Yellow Pine - White
Fir belt.
– north in south sierra
– south slope in few north sierra, not
water limited.
• Closed Cone Tree
– Importance of fire to reproduction
– Other means for cones to open
• We’ll See the Grizzly Giant in
mariposa grove
Grizzly
Giant
• Mariposa
Grove
Upper Zones
• Lodgepole Pine - Red Fir belt 6,000 - 8,000.
– You see some of these plants at Crane Flat
• Sub-alpine 7,000- 10,000
– Great to view over summit to Tuolumne
Meadows
• Timberline- zone above which no trees
grows due to limited soils, severe weather.
• Alpine Fell-field 10,000 - 13,000
– We saw a recreation of this zone in U C
Botanical Garden
Upper Valleys
Forest helps make their own
climate by shading soil
• Shaded soils retain more moisture, more
protected from wind.
• Excludes many species from growing
underneath a closed canopy layer.
• Shade leaves grow thinner, larger than
leaves grown in full sun.
• Light gaps “release” shaded saplings and
they respond rapidly.
• Tapered shape of young trees allows
lower leaves to still get light.
Geology
of
Sierras
Rocks divided by formation
periods:
• Prebatholithic rocks were old sea floor
sediments well above newer granitic
batholith of the current sierras.
– Formed older proto-sierras
• Batholithic rocks formed by magma
formation 10 miles below ground by
subduction of Pacific Plate under North
American, around 160-65 million years
ago
– 100 million year process!!.
Uplift begins about 80 million
years ago
• Pushing up prebatholithic rocks forming
Protosierras.
– Erosion carried debris westwards as it rose,
creating a flat terrain of rolling hillsides by 40
million years ago.
• Protosierras were probably only a few
1,000 ft in elevation, like today’s foothills.
– eastern fossils show no evidence of
rainshadow.
• 20-5 million years ago extensive volcanic
period in southern Cascades and northern
Sierras, with lava flowing over relatively
flat terrain
Major Uplifting More Recent:
• 3 MYA major uplifting and tilting on
angle
– gentle western, steep eastern slope.
– Accelerated erosion, removed upper
layers, forms deeper river valleys.
– Still continuing, future sierras will be
still higher !!
• uplift in Southern Sierras greater
than Northern, higher peaks formed
there.
•From: The Geologic Story of Yosemite National Park
•N. King Huber, Ph.D.
Increased precipitation
• erode upper layers, revealing granite rock
below.
• leaves a few Roof pendants, the remains
of prebatholithic rocks perched on top of
granite.
– mostly on northern half of Sierras, less
uplifting and erosion.
• metamorphic rocks
• fills in central Valley with 10,000-30,000
feet of alluvial debris
Contact zones
• Formed between metamorphic and granite
rocks have mineral veins.
• At time of intrusion of granitic rocks, heat
from magma drove water towards surface
carrying minerals within it, forming veins
in fractured overlaying rocks.
• Gold and quartz moved in with hot water,
eroded out, as collected in stream, river
sediments
• 1849 Gold Rush into Sierras
– Panning and later hydro-mining
Postbatholitic rocks
• Newest rock formations
• Sedimentary
– eroded rock debris washed westward,
still today.
• Volcanic in areas
Ice Ages in Sierras
• Deepen valleys by Glacier action
• Rain erosion forms “V” shaped valleys.
– Sierras include watershed from Kern River in
the South to Feather Rivers in the North.
• Glacier erosion forms “U” shaped valleys.
• Pre-Tahoe and other Glacial periods
– Several earlier glacial periods as far back a 4
million years.
– Cut Yosemite Valley
• Tioga Glaciation- Most recent
– Began about 30,000 to 60,000
– Peaked 20,000-15,000 years ago
– Glaciers in Yosemite only reached to Bridal
Veil, but was 4,000 ft. deep.
Glaciers in Yosemite
•
•
From: The Geologic Story of Yosemite National Park
N. King Huber, Ph.D.
Hanging Valley
Lava in Old River Bed
V-Shaped Valley
U-Shaped Valley
Yosemite
Valley Floor
• U Shaped
• Convergence
of 2 or more
glaciers
• Filled in with
alluvium
• Meadows and
Forest
Glacial Erosion
• Leaves moraines
• Lateral, terminal, medial
• Erractics-rocks carried in ice,
dropped and left behind as glacier
retreats, out of place
• Hanging Valleys – Side valley cut off
by passing glacier below
• Lakes form in tarns
• Leave no soil, primary succession.
Erratics on Olmstead Point
Upper Meadows
Re-growth after fire
•
Yosemite
Trip
http://mvz.berkeley.edu/Grinne
ll/2004_Report/index.html
• Uses field report data from between
1914 and 1920
• Compare to now to see effects of
development, climate change on
Yosemite National Park.
Some changes to the valley
floor:
• Altered fire cycle
• Fewer Mountain lions, more deer
How humans, vanishing cougars changed Yosemite
David Perlman, Chronicle Science Editor
Friday, May 2, 2008