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Trees of the Sepulveda BasinShrubs and PerennialsAquatic PlantsWeeds of the Sepulveda BasinVegetation Management in the Sepulveda Basin
 
FLORA
  Thousands of native plants have been planted in the Sepulveda Basin Wildlife Reserve. Many other plants have “volunteered” – meaning grew
on their own from seeds, underground shoots, or from broken pieces of plant that rooted and took hold. While certain native plant have “volunteered”
(coyote bush, mulefat, California walnut, elderberry, western ragwort, and mugwort), many non-native plants have also taken advantage of disturbed soils or
the remoteness of certain areas to invade and in some cases threaten to take over the landscape. There are approximately 100 native California plants
found in the Wildlife Reserve, and probably an equal number non-native plants and weedy species.
 
     
 
Since the Reserve is located in a flood control basin that does indeed flood, weed management will be an ongoing practice: every time the Basin floods,
every weed seed (and native seed as well) in the upper L.A. River watershed gets caught in the Basin. As the flood waters recede, a one-half to one-inch layer
of silt is left, covering up every portion of the Basin that was flooded. This silt layer is the perfect example of exposed disturbed soil, the kind of condition that
weed seeds are highly adapted to and thus can easily germinate…that is, if the seeds are also exposed to light.
So weed management will be an ongoing project in the Basin.
 
     
 
Restoration vs. Revegetation
 
 
Since there is no detailed record of the plants that once occupied the Basin, and since there really weren’t any populations of existing native plants
in the Basin (except for mulefat, coyote bush, and one willow in some of the channels), nearly all the native plant material that was introduced
was purchased from nurseries or contract growers. It is unknown exactly where these plants originated.
 
     
 
Thus, even though the Wildlife Reserve has the “look” of a “natural” habitat, it would be incorrect to state that we have “restored” the habitat.
Just the fact that there is a physical dam structure that floods creates an “un-natural” environment; it is certain that the L.A. River flooded in the past,
but the unfettered floods changed the river course over time. Of course nowadays such a change in the river course would have
devastating effects to the homes and businesses that now fill the San Fernando Valley.
 
     
 
Furthermore, while there are native trees and shrubs in the Wildlife Reserve, there are very few native annual plants.
Until a full complement of annual plants are found in the Basin, we can only say that we have revegetated the area with native plants,
and that we have created a mostly native riparian forest, shrubland, and aquatic habitat.
 
     
 
That is not to say that what has been created isn’t valuable. And the increasing cover of native trees and shrubs provides habitat for the native fauna,
and that native fauna is increasingly become more populous and diverse over time. Originally there were few insects in the Reserve,
especially top predators such as spiders and carnivorous insects such as praying mantids; now they are common.
 
     
 


above, most common plants include mulefat, coyote bush, and cottonwood.

 
     
 
 
     
 
PLANT COMMUNITIES
 
     
 
There are five main plant communities in the Sepulveda Basin Wildlife Reserve: riparian forest, riparian shrubland, oak and walnut woodlands, coastal sage scrub,
and aquatic. Each community includes various age stands (and that is a good thing), due to different planting years and the effect of fires.
 
     
 
Riparian Forest
 
 
A forest is recognized by a closed canopy, meaning that the leaves of individual trees touch and overlap. In the North Reserve, the cottonwood trees along
Haskell Creek form a closed canopy at the David Lewis grove and between the bridges (along with willows). In the South Reserve willows, box elder, cottonwoods,
and non-native trees (evergreen ash in particular) form a closed canopy along Haskell Creek. There is also a riparian forest surrounding the pothole pond in the
South Reserve. Due to the deciduous nature of the riparian forest trees, the leaves that fall in autumn create a deep leaf litter (mulch) that eventually turns into soil,
but also covers the ground and suppresses weed growth.
 
     
 
Riparian Shrubland
 
 
In the Sepulveda Basin, especially in lowlands, native shrubs such as mulefat and coyote bush dominate. This plant community is most prevalent in the
South Reserve. There is also a significant stand of mulefat and coyote bush around the Wildlife Lake, and an open shrubland of scattered coyote bush and mulefat
can be found east of the Wildlife Lake in the “uplands” of the Wildlife Reserve. Western ragweed and mugwort can also be found in this plant community.
 
     
 
Oak and Walnut Woodlands
 
 
A woodland is recognized by scattered trees (or large shrubs) that as a rule don’t touch each other; thus a woodland is characterized by its open canopy.
The young oak trees planted out between Woodley Ave and Haskell Creek in the North Reserve are almost mature enough for the area to be described as an
oak woodland. On the north berm of Burbank Blvd (east of the tunnel) the oak trees are so dense that they nearly form a closed-canopy forest, but there are so few
that woodland better describes the area. In the South Reserve, there are widespread oak trees that can be described as a woodland. California walnut trees
have volunteered and been planted out in various areas in the Wildlife Reserve, and often occur with the oak trees.
In southern California, oak and walnut woodlands are often located on the cooler, north slopes.
 
     
 
Coastal Sage Scrub
 
 
Often known as “soft chaparral” because the plants are not as tall as in true chaparral, plants common to this plant community have been planted mostly in the South Reserve along the south-facing berm of Burbank Blvd. Many coastal sage scrub plants are drought deciduous, meaning they drop their leaves in the hot summer months, and grow new leaves after the first rains in the fall. Plants typical of coastal sage scrub include sages (in the mint family) such as black, white and purple sages, California sagebrush (in the daisy family), toyon, laurel sumac, lemonadeberry, sugarbush, prickly pear cactus, California buckwheat, and bladderpod.
 
     
 
Aquatic Plant Community
 
 
With a creek, a lake, a pond, and a river, the Sepulveda Basin Wildlife Reserve has a diverse and fecund aquatic plant community.
cattails and bulrushes are prevalent in all wetlands. Willow water-weed and water smartweed grow in the pond and lake and provide sustenance to waterfowl.
Because all of the water bodies in the Sepulveda Basin Wildlife Reserve are being charged with reclaimed water that is relatively warm and full of nutrients,
runaway algal bloom is always a threat during hot periods during the summer months.
 
     
 
 
     
 
COMMON NATIVE PLANTS
 
     
 
In a way the Sepulveda Basin Wildlife Area is an ongoing experiment. Native plants are planted in different areas with the hope that they will survive, thrive and in the best scenario, produce viable seed that can disperse and spread the distribution of appropriate native plants. Because of the heavy clay soil and occasional flooding, only certain species will really do well. The plants listed below are the ones that have shown longevity in the Basin.
 
     
   
 
Fremont cottonwood
Black cottonwood
California walnut
Western sycamore
Box elder
Arroyo, red and sandbar willow
Coast live oak
Valley oak
Arizona ash
 
     
   
 
Mulefat
Coyote bush
California wild rose
Coffee berry
Davidson’s bush mallow
Mexican elderberry
California grape
Golden currant
Milkweed
Bladderpod
White sage
Black sage
Purple sage
California sagebrush
Toyon
Lemonadeberry
Sugar bush
Laurel sumac
Prickly pear cactus
California blackberry
 
     
   
 
Ditch goldenrod
cattail
Bullrush
Willow water-weed
Water smartweed
 
     
 
 
     
   
     
 
Non-native weeds and invasive plants are a constant threat to overtaking the native plants in the Wildlife Reserve. Ongoing weed control projects are necessary.
Because of regular flooding and a history of agriculture, there is a large seed bank of weed seeds in the soil of the Basin. Disturbance to the soil exposes the
weed seeds to light and with rainfall the seeds will germinate. Grasses can germinate from small portions of the stem, so flooding can also introduce
plant material that can germinate once it comes to rest in the silt deposited after a flood.
 
     
 
Weeds in the Basin range from annuals (mustard, wild radish, grasses, thistles, etc.), to perennials (bunch grasses, fennel, pepperweed and poison hemlock), to shrubs (pampas grass, giant reed), to trees (tree of heaven, evergreen ash, palm trees, black locust, and eucalyptus).
 
     
 
While it is likely that non-native annuals will be a permanent feature, they can be minimized in certain areas and eventually (hopefully) replaced by native shrub cover
and native annuals. The perennial weeds and trees that left uncontrolled can invade and eventually infest and overtake the native vegetation must be
actively monitored and (again hopefully) eventually eradicated.
 
     
 
Because funding is limited for weed control, a management plan has evolved over time to focus on the worst offenders, and certain areas have been slated for a higher degree of weed control than others. There is little toleration for perennial weeds in the North Reserve, although the perennial non-native bunchgrasses are always popping up here or there. Non-natives mostly eliminated from the North Reserve include tree of heaven, castor bean, evergreen ash, fennel, milk thistle, and palm trees. giant reed and castor bean are not tolerated throughout the entire Basin, and control using herbicide is ongoing when necessary.
 
     
 
The west extension of the North Reserve between Haskell Creek and Woodley, an area where compensating excavation took place, is very weedy.
Fennel has been partially controlled, but poison hemlock, mustard, thistles, horehound, Russian thistle, and perennial non-native grasses dominate the landscape,
with scattered (but increasing) coyote bush, elderberry, mulefat, and oaks trees.
 
     
 
The South Reserve has many weed problems too. Haskell Creek is choked with evergreen ash, that has now emerged above the willow canopy and will likely shade out the natives unless the non-native trees are removed. Tall eucalyptus trees are scattered, along with a number of oddball non-native trees (pines, black locust, elm, etc.). Horehound is abundant. The area adjacent to the dam outlet is frequently disked, and in those fields very bad weeds such as yellow star thistle and perennial pepperweed have been found; this area is regularly targeted for herbicide treatment. giant reed occasionally appears and is treated.
 
     
 

above, castor bean and tree of heaven invade willows.

Exotic Trees
 
 
Tree of heaven
Evergreen ash
Palm tree
Eucalyptus
Black locust
 
     
   
 
Pampas grass
Horehound
Fennel
Poison hemlock
Perennial pepperweed
giant reed
Johnson grass
Harding grass
Smilo grass
Castor bean
Curly dock
 
     
   
 
Mustard
Wild radish
Bull thistle
Milk thistle
Sow thistle
Tocalote
Yellow star thistle
Horseweed
Prickly lettuce
Sweet clover