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 The South
Fork Valley is a mixture of floras. Central to the valley is the
cottonwood/willow riparian forest along the South Fork Kern and its
tributaries. The perennially flooded areas next to the forest consist of
emergent freshwater wetlands. The ephemerally flooded areas are either
perennial grasslands or alkali marshes. Uplands support a mixture of
Sierran, San Joaquin Valley, and Mojave Desert vegetation. When Joseph
Grinnell surveyed the South Fork in 1911 he remarked in his field notes
the difficulty in separating the vegetation into distinct zones as
classified by Merriam. In the eastwardly reaches and along Kelso Valley,
large swaths of Joshua tree woodland are interspersed with tracts of
scrubland mostly consisting of rubber rabbitbrush. Upslope of the valley
floors, the vegetation quickly transitions into conifer woodlands. From
the southeastern edges of the South Fork Valley the highlands are mostly
pinyon/juniper forest. On the northwestern edge the highlands transition
into gray pine/oak woodlands. Although, as Grinnell discovered there are
few distinct boundaries of vegetation once you veer away from the
riparian forest.
Flora
So far 322
species have been documented on the contiguous preserve and several of
these are rare or sensitive species. Three rare flowering plants have been
found along Fay Creek, Pygmy Poppy, Hoover's Woolystar, and Kern Dwarf Brodiaea. A third rare
plant was discovered in 2008 on the nearby Canebrake Ecological Reserve,
Crowned Muilla, this is the first time this plant has been found west of
the eastern crest of the Sierra Nevada. Audubon staff conduct a census
each spring to search for new plants on preserve property.
HABITATS
Wetlands
The South
Fork Kern River contains significant freshwater wetlands comprised of
riparian forest, marshes, and ponds that are being restored by Audubon
and its neighbor and partner the California Department of Fish & Game.
The length of the floodplain encompasses 3,495 acres of
cottonwood-willow riparian forest and 407 acres of wetlands and ponds.
These areas are transient in character due to variable water delivery
with upstream water users removing many acre-feet for irrigation and
domestic use each year.
Permanent
fresh emergent wetlands
Emergent
wetlands contain vegetation with that can only survive with roots
submerged in water and with their reproductive and photosynthetic parts
in the air. Permanent emergent wetland plants common to the Kern River
Preserve include: tule (Scirpus acutus), cattail (Typha
latifolia), sedges (Carex spp.), mosquito fern (Azolla
filiculoides) and rushes (Eleocharis spp). The South Fork
Valley receives the surrounding mountain alluvial wash creating a
relatively flat, level valley floor. Here permanent wetlands are
associated with semi-permanent ponds. The Prince Pond is the largest
permanent pond/marsh system on the Kern River Preserve. It occasionally
goes dry in drought years when ground water overdraft occurs. The
closest permanent wetland, Mariposa Marsh and Gator Pond are dependent
upon water delivery through the extensive canal system developed in the
late 1800s.
Seasonal
fresh emergent wetlands
Although
perennial wetlands are few in the South Fork Valley, seasonal wetlands
are common. These areas pond up for shorter periods and support
perennial vegetation that is more deeply rooted. The edges of these
areas also support annual vegetation. You can find perennial rye grass (Lolium
perenne) in the edges of the temporary impoundments to spike rush (Eleocharis
macrostachya) in the center. In the South Fork Valley these wetlands
most often occur in lowland pockets in perennial grassland and shrubland
habitats. The Kern River Preserve and neighboring Canebrake Ecological
Reserve preserved large swaths of seasonal wetlands and with the
purchases of the Sprague and Alexander Ranches an even greater amount.
These ponds support breeding ducks and migratory shorebirds find
temporary refuge. Alkali meadows on the preserve and throughout the Kern
River Valley support several populations of the rare alkali mariposa
lily (Calochortus striatus).
Cottonwood/willow riparian forest
Riparian
forests are riverbank ecosystems that contain water dependant woody
plants and are one of the most diverse habitats in the world. It is easy
to judge where water flows permanently in the South Fork and Kelso
Valleys and where it becomes ephemeral by the presence or absence of
white alder (Alnus rhombifolia). The water table must remain
consistently high for all riparian species although some like the alder
die out quickly if any depletion of surface water occurs. There are four
layers to the South Fork Kern River cottonwood/willow riparian forest:
canopy, sub-canopy, understory, and herbaceous.
The mature
canopy of the Fremont cottonwood / black willow forest reaches 80-90
feet in height. The sub-canopy reaches the middle section of the canopy
with large shrubs and trees. The height of the subcanopy along the south
fork could reach heights of between 25 to 75 feet but generally due to
the dense overstory; red willow, white alder and Oregon ash grow to less
than their full height. The understory consists of a mixture of woody
shrubs and along the South Fork is predominantly wild rose, elderberry,
sandbar willow and mulefat. The herbaceous layer can contain both annual
and perennial vegetation with grasses, sedges, and dichotomous herbs.
Several aggressive exotic trees, shrubs and perennials are continuously
threatening to colonize the South Fork, but both Audubon and the
California Department of Fish & Game conduct annual exotic species
removal programs to prevent this from happening.
Valley
Grassland
Valley
Grassland consists of both annual and perennial grassland. Grasslands
are open habitats with herbaceous vegetation. Annual Grassland habitat
occurs on flat plains to gently rolling hills. Changes in annual
grassland vary from year to year depending on rainfall. Spectacular
variation in colors with the shifting seasons and because of variable
rainfall from year to year, are characters of this habitat.
The
Mediterranean weather pattern of hot dry summers and cold wet winters
creates the optimum condition for early germination of annual plant
seeds resulting in rapid blooms and short-lived plants. During abundant
rainfall years, sensational wildflower displays in annual grassland are
common. Yet, without management several years of above normal rainfall
can reduce the number of wildflowers due to the overgrowth of introduced
grasses and forbs.
Annual
Grassland has experienced significant change since the arrival of people
of European descent with the introduction of cattle and sheep in the
early 1800's. The brown hills of California are the dried remains
of most of these exotic annual grasses. Dominant species include: wild
barley, ripgut brome, red brome, cheatgrass, and foxtail brome. Common
forbs include broadleaf filaree, redstem filaree, annual burweed, true
clovers, bur clover, popcorn flower, and a multitude of native
wildflowers. The slopes and drier areas of the Kern River Preserve
support large swaths of annual grassland.
Perennial
grassland is most common where the rainfall or runoff exceeds 60 inches
per year. This type of grassland is found throughout the Sierra Nevada
in mountain meadows or adjacent to streams and rivers in the mountains
and valleys. It grows best in moist, lightly grazed, or relic prairie
areas. Perennial plants generally bloom later in the spring than annuals
and may continue to bloom through the fall. Typical plants of the Kern
River Preserve’s perennial grasslands include: Alkali sacaton, desert
needlegrass, wild rye, one-sided bluegrass, and scratch grass.
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