Grasslands and Prairies - The Santa Barbara Botanic Garden D.Wilken... · South America Pampas...
Transcript of Grasslands and Prairies - The Santa Barbara Botanic Garden D.Wilken... · South America Pampas...
Grassland
Dominated by grasses (Poaceae) and
grass-like plants (sedges, rushes)
30 – 40 % of world land surface
Climate composed of moderate
precipitation (10 - 50 inches/yr) and
periodic drought
Other environmental factors
Fire
Grazing
North America Prairie, Great Plains Grasslands
Eurasia Steppe
South America Pampas
Temperate Grasslands
Subtropical to Tropical Grasslands
South America Cerrado, Llanos
Africa Savanna, Veldt
Australia Mitchell Grasslands
From the historic French word for a tree-less meadow or
pasture co-dominated by perennial grasses and forbs.
Prairie
Steppe
Generally used by North American ecologists to describe a
tree-less vegetation of grasses, dicotyledonous herbs, and
small shrubs.
From the Russian word “степ” for an extensive, flat
grassland.
Sometimes used by North American ecologists to describe
a grassland composed of short statured, perennial grasses
or bunch grasses.
Temperate Grasslands
Cold season alternating with Warm to Hot season
10 – 35 inches of annual precipitation alternating with
drought
Deep, porous soils (e.g., loess)
Cool to Warm seasons alternating with Warm to Hot
seasons
20 – 50 inches of annual precipitation alternating with
drought
Soils vary from deep to thin, porous to clay
Subtropical to Tropical Grasslands
Adaptations
perennial, cespitose habit
thin, narrow leaves that grow from the base
deep, compact root systems
G G G G G G G G G
“Grazing”
Mixed Browsing and Grazing
Grazing: feeding primarily on
grasses and grass-like plants
Browsing: feeding primarily on
forbs (dicotyledonous herbs)
and shrubs
Mule Deer diet
4 – 15 % grasses
15 – 30 % forbs
75 – 90 % shrubs
Pronghorn diet
5 – 45 % grasses
25 – 50 % forbs
10 – 60 % shrubs
Elk diet
45 – 60 % grasses
11 – 40 % forbs
25 – 30 % shrubs
Grazing and Fire Remove Biomass
reduce competition
enhance seed germination
return nutrients to the soil
remove or kill shrub and tree seedlings
Grazing
Fire
Coastal Prairie
northern coastal California north to southern Oregon
highest plant species diversity among California
“grasslands”, composed of a mixture of grasses, sedges,
and forbs
deep, porous, sandy soils of low-lying valleys
historically promoted by Native American burning practices
and grazing by elk
Danthonia californica
California oatgrass
Deschampsia cespitosa
hair grass
Festuca californica
California fescue
Iris douglasiana
Douglas iris Carex tumulicola
foothill sedge
Ranunculus californicus
California buttercup
California Grasslands
Frederick Clements’ (1934) “Bunchgrass-Grazing”
hypothesis.
Bunchgrasses once dominated the Great Central
Valley and adjacent foothills but were eliminated by
excessive livestock grazing and too frequent fires.
Needle grass (Stipa, Nassella)
Bunchgrass Steppe
Clements based his hypothesis on "relict" stands of native
bunchgrasses he found along railways and outside of fenced
pastures.
He assumed that the original vegetation was like that of
central North America, i.e. composed of perennial grasses.
Clements emphasized the role of over-grazing, but ignored
that fire promotes the establishment and persistence of
needle-grass.
Fire
Proponents of the bunchgrass-grazing hypothesis tended to
ignore historical observations and the significance of alien
Mediterranean invasive species.
18th Century Expeditions and Observations
Gaspar de Portolá Expeditions, 1769-1770, 1772
Fr. Juan Crespí, Miguel Costansó, Pedro Fages
Juan Bautista de Anza Expeditions, 1774, 1776
● observed burning by Native Americans, which enhanced
open habitats and barren areas or areas dominated by
grasses
● described open areas using words (pasto, yerbas, zacate)
that often referred to forage or dry herbaceous vegetation
● observed herbivores that are now known to be deer,
pronghorn, and elk
19th Century Expeditions and Observations
Gabriel Moraga, 1806 (Fr. Pedro Muňoz)
Thomas Coulter, 1832 - 1834
Pacific Exploring (Wilkes) Expedition, 1838 – 1842
John C. Fremont, 1844, 1848
Edwin Bryant, 1848
William P. Blake, Pacific Railroad Survey, 1853-1854
William H. Brewer, California Geological Survey, 1860 – 1864
John Muir, 1870+
Spring months: grasses and many wildflowers;
forage
Summer months: few grasses, few wildflowers;
forage sometimes sparse or completely absent
19th Century, Coast and Coast Ranges
19th Century, Interior Valleys (San Joaquin)
Spring months: vast wildflower displays; grasses and
forage rarely mentioned, except along rivers.
Summer months: herbaceous vegetation dried, no
forage, landscape often described as barren or destitute
California Valley Grassland
Annual Grassland
western San Joaquin Valley Hungry Valley
Considered by ecologists as a unique grassland, because
it is dominated almost entirely by invasive, alien species
from European Mediterranean.
Annual Grasslands
Dominated almost exclusively by
alien, Mediterranean annuals
Avena fatua
wild oat
Avena sativa
culitvated oat
Brassica nigra
black mustard
Medicago polymorpha
burr clover
Bromus diandrus
ripgut brome
Bromus hordeaceus
smooth brome
Hordeum murinum
wall barley
Malva parviflora
cheeseweed
Erodium cicutarium
redstem filaree
Mediterranean Invasive Annuals
Arrived in California during the late 18th and 19th
centuries
Pre-adapted to California’s climate but differing
from the native California flora by their advantage
in having
rapid seed dispersal
recruitment from seeds at high densities
rapid early season growth rate
Most invasive annuals, however, have relatively low
seed longevity as compared to native annuals
Carrizo Plain
Carrizo Plain National Monument, a “remnant of the
Central Valley’s former vast grassland”
Carrizo Plain - Carrisa Plains
1850. First settlement by sheepherders (Saucito Ranch)
1853. US Railroad Survey names “Llano Estero” and “Carrizo
Ranch”
1876+ Sheep and cattle grazing; potato, wheat, and barley
farming.
1940s Farms and ranches begin to fail
1980+ Federal land acquisitions
2001. Carrizo Plain National Monument established
Saucito Ranch, Soda Lake,
Temblor Range
Carrizo Plain
Completely enclosed basin with alkaline clay or clay
loam soils
Vegetation a complex mosaic of:
Atriplex polycarpa (allscale saltbush) shrubland,
and
annual Mediterranean grassland
Scattered Stipa (Nassella) and Poa secunda bunch
grass mixed with Juniper-Ephedra shrubland
occurs on adjacent slopes and hills.
Great Valley Grasslands State Park
wetlands, sloughs, and floodplain of the San
Joaquin River east of Gustine, Merced County
California’s Grasslands
Original grasslands are not as extensive as
previously thought.
Coastal grasslands and prairies may have been
significantly influenced by Native American
burning practices. In the absence of fire, such
grasslands are subject to invasion by shrublands
and forest trees.
Pre-European vegetation of the Great
Central Valley, especially the San Joaquin
Valley with clay soils, probably was not
dominated by grasses.
California’s Grasslands
Some landscapes previously thought to be
grasslands actually may have been
composed of dicotyledonous annuals
(forbs).
The most common, widespread grasslands
in California are effectively dominated by
alien, Mediterranean grasses and forbs.