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Vegetation of the South Fork Valley


NOTE: There is no collecting, fishing, or hunting on the preserve. If you see any animal or plant on the preserve, please take only pictures and memories. Do not disturb nesting birds. Do not go off trail.

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.


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.



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.

Kern River Preserve in Weldon, California. Open every day of the year from dawn to dusk. Support our efforts to protect the South Fork Kern, join the Audubon Kern River Preserve.

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This site was created on October 21, 1998. Please Email to make comments or offer suggestions.