Bio126 Bio126 The Great Central ValleyThe Great Central Valley

Great Central Valley Characteristics: Largest Plain West of the Rockies

430 miles long 75 miles wide (varies)

In Rainshadow of Coastal Mountains mostly dry land with ribbons of wet areas

along rivers. Spilt into Sacramento and San Joaquin

Valleys by Rivers, meet in Delta

Great Central Valley – topography: Broad flat plain Ringed with rolling foothills on all sides Slightly below sea level in middle, in the

Delta Region – salt water flows in. Rises to about 400 ft. elevation at extreme

southern and northern ends. Filled with deep alluvial layers. Remains of

proto (old) Sierras washed into former inland sea. Up to 30,000’ thick.

Great Central Valley –Latitudinal Rain Gradient Long enough to have differences in

annual rainfall due to Hadley cell positions. North- Redding 38” Central – Sacramento 18” South – Bakersfield 6”

Rainshadow makes inland drier than coastal areas of same latitude

Great Central Valley –The Major Community types: Grasslands

Had 22,000,000 acres Now just 1 % remain

Riparian Corridors Had 4,000,000 acres Now 6% remain

Fresh water marsh Had 975,000 Now 11% remain

Great Central Valley – Seasonal Changes Major flooding now rare. Most rivers diverted or dammed higher up – Rivers channelized Great seasonal lakes and marshes no longer

form. Early settlers moved around by boat in

winter. Cholera, etc, seasonal problems. Marshes

began to be drained.

Central Valley Drainage basin Drains west slope of Sierra

Many major rivers Drains east slope of coastal mountains

Smaller ‘rivers’, many called creeks Drains southern cascades

via Pit River into Shasta Lake then in Sacramento River

All drain into Delta, to SF Bay - Ocean

Sacramento Valley From the Delta North Sacramento River the major river fed

by: American Feather Yuba Shasta

San Joaquin Valley From the Delta South San Joaquin River the major river fed

by: Merced Tuolomne Stanislaus Mokelumne Cosumnes

River Deltas Delta formed at each of the river

junctions on a flat plain Large areas of marshland once

important part of Central Valley Ecology

Central Valley Grasslands Rapidly changed from perennial bunch

grasses to introduced annual grasses Pushed Blacktailed Deer and Tule Elk out of

valley Deer moved to foothills, migrating up into

and down from Sierras Tule Elk moved into marshes as a last

refuge. Last habitat as marshes were drained Fewer than 10 remained in lake Buena Vista

Perennial Bunch Grasses Slow growing, long lived Deep rooted, tall grasses Set seed in summer Poor competitors Evolved without grazers Large “fountains” or bunches of year-round

grayish green grass Lower fire intensity Open spaces in between bunches where

bulbs and annuals wildflowers grew.

Annual Grasses Brought over from Spain with cattle and

sheep in hides and feed Great competitors Rapid germination and seedling growth Shallow roots quickly dry out top soil Several hundred per square foot Short lived, not as nutritious

(Terrace) Vernal Pools A superficial clay hardpan layer in soil traps

water in depressions. Dry soil slowly exposed later in spring as

pool dries Water and lower soils become salty Many Endemic species Relict spp. left from moister climate with

summer rain. See also Text pg. 395-6

Fresh Water Marshlands Shallow areas flooded (at least

seasonally) with fresh water Commonly bordered large shallow

lakes Bands of vegetation:

Macrophytes – floating plants Reed-like Plant Border Higher ground – Riparian species

Macrophytes “Larger” than algae, but still small

plants Azolla a small water fern with nitrogen

fixing bacteria Lemma duckweed can completely

cover lakes in summer Water Hyacinth a new introduced pest

Reed-like plant border Deepest water (only up to 4’) has

cattails. Hollow Stems with “sausage-like” stalk of flowers / seeds

Bulrushes or Tules common Sedges have triangular stems

Higher Ground Has shrubs, and small trees like

willows

Riparian or Gallery Forests A nearly closed canopy forest with a river or

stream running down through it. Very narrow band along waterway, within sight of water.

Streams and rivers had many shallow branching courses, not in channels like today. SOME FORESTS UP TO 10 MILES THICK !

They remain wet year-round with snow melt run off.

Gallery forest photo

Riparian Forest Tree Species

Valley: Valley Oak, Cottonwood, Alder, Willows,

Oregon Ash, Boxelder, Walnut, Sycamores, Maple

CA Grape, Poison Oak, vines growing up tall trees.

Higher elevations: Alder, Willows, Aspen, Bigleaf Maple,

Dogwood

Riparian Forest Characteristics Cold air drainage with fog in winter.

Lows 32 – 38 F (-4 to 0 C) common Have broad flat leaves, need lots of

water, especially in the summer Many have Nitrogen fixing bacteria in

roots Wind currents carry pollen and later

cottony winged-seeds down stream Winter deciduous

Riparian Forest Trees Adapted to floods by sprouting

vigorously from stumps Broken limbs buried in floods can root

and sprout, dispersing the trees into new soil layers.

Remnants of Former Climates Migrated into California when climate

was much mild and wetter. From East Coast hardwood Forest: Maple, Boxelder, Ash, some Willows

From Semi-dry Climate, from southwest: Sycamore, Cottonwood, other Willows

Riparian Habitat Had many summer-flowing rivers V shaped valleys too desirable for

dams !! Super-fertile soils now mostly orchards Water from dams provides irrigation Most rivers mere remnants of flow and

size in flood controlled channels.

Southern Central Valley Lakes Lakes NOT flowing into San Joaquin Large Shallow lakes fed by winter rain, snow

melt Tremendous migratory bird populations 1,000’s acres of marsh along shores Slight rise in valley floor trapped water in

southern end of valley Tulare Lake fed by (N to S) Kings,Tulare and

Kaweah Rivers Buena Vista & Kern Lakes fed by Kern River

Foothill Ecotone Ecotones are abrupt meeting places of

different community types, not a gradual transition

Often have high species diversity Have species for each habitat, plus Have species only found in ecotone

Mix marsh, Riparian, Grassland species