Santa Barbara New-Press
The stark vertical relief of our local mountains show how
relatively quickly these forms have been built up. The forces
of wind and water round all edges and wear down every grade.
The dramatic features of the Santa Ynez Mountains show their youth
precisely because cliff faces and narrow canyons have had less time
to erode. The mountains are achieving in stages what
California has been working toward for the last 200 million years:
a dry life, out from under the Pacific Ocean.
Over the course of a human lifetime, of course, we want to slow
down the process of erosion as much as possible. Our success
at gardening and feeding ourselves depends on good soils.
Vegetative cover helps preserve soils from washing away in two
main ways. First it breaks the impact of rain. Falling
water has a small but definite force (20 mph is possible, depending
on many factors). Each direct impact will separate the smallest and
lightest particles of soil from the rest. Such material will
often move with the splash of the droplet, becoming mobile in the
runoff. Rain on bare soil with substantial runoff will result
in more rocky, sandy soil, as the finest clay particles are washed
away.
Brush cover, even very low cover, interrupts and absorbs the
energy of falling water. As it clings to leaves and stems and
continues its fall, the kinetic energy of the droplet is a fraction
of what it carried in its first fall of several hundred or several
thousand feet.
The second main way vegetative cover helps preserve soils is
well-established plants provide a rei4nforcing network that helps
resist water flowing over the surface of the soil. Like rebar
in concrete, the wandering, dividing roots of the plants grow
through and past one another, stabilizing not only the plants
themselves but the soil as well. Living roots are more
effective at holding the soil, but dead roots are better than
nothing. Removing dead tree stumps is not helpful if you are
trying to keep the soil in place.
The bulk of a plant's roots are in the first one to three feet
of soil, with most of it in the first 12 inches. While some
California native shrubs and trees have tap roots, roots that
extend downward at 45 degree angles or even straight down, they are
the exception to the rule of a great saucer-shaped root mass around
the plant's main stem.
In undisturbed soils, the network extends far beyond the plant's
roots. Most perennial plants around the world have evolved
relationships with soil fungi. Many thousands of species of
soil fungi exist, each with a network of root-like filaments
(called hyphae) which are the bulk of the organism. Mushrooms
that emerge from the soil surface are merely reproductive
structures and just a fraction of the fungal body. Fungi that
attach to the roots of plants are symbiotic, taking sugars
manufactured by the plant and sharing water and nutrients absorbed
through the wide spreading hyphae. This network of
interconnected, interlaced hyphae taken together provide a more
solid base to grow in than the aggregated soil and add to the
holding power of the plants.
Most of the native vegetation in chaparral and coastal scrub are
excellent for erosion control as the harsh conditions (i.e. baking
sun and low rainfall) have forced these plants to adapt with an
extensive root system. While tap roots are helpful, a
shallower system extending 30-40 feet around the plant is still a
major force in stabilizing soils. It is also an efficient
water-saving adaptation because the greater the surface area of the
roots the more water the plant can absorb in small rain
events.
Some of the larger shrubs that will work well for erosion
control are manzanita (Arctostaphylos) and wild lilac
(Ceanothus). Both groups of plants have many named,
cultivated varieties (cultivars) available even from
mainstream nurseries. Manzanitas bloom in winter with
delicate white flowers. Wild lilacs bloom in shades of blue
or white in early spring. But as large a group of varieties
as this represents, it barely scratches the surface of what is
possible. Other great shrubs for erosion control are
coffeeberry (Rhamnus and Frangula), which are evergreen with
colorful berries; chamise (Adenostoma fasciculatum), one of the
tougher shrubs that occupies rocky, southern-facing outcrops; and
quick growing shrubs like California sagebrush (Artemisia
californica) and coyote brush (Baccharis pilularis). Of
course, our coast live oak (Quercus agrifolia) is one of the best
stabilizers of slopes in our part of the state.
Large woody shrubs are not the only great choice for stabilizing
slopes. Many smaller, more herbaceous plan ts grow in
colonies, spreading by underground stems (rhizomes). These
dense, spreading root systems knit soils beautifully. Such
plants include chaparral mallow (Malacothamnus), tall with soft
pink flowers, deerweed (Acmispon glaber, formerly Lotus scoparius),
a quick fire-follower to two or three feet in height with yellow
flowers fading orange, California fuchsia (Epilobium), with late
summer blooms of red-orange, mugwort (Artemisia douglasiana) able
to deal with dry up-slopes or moist streambeds, and goldenrod
(Solidago) with three foot stalks topped by many small golden
flowers, just to name a few.
For really impoverished soils, rehabilitation may be
necessary. Such efforts almost always include building a
more organic soil layer with mulch. Landscaping companies,
like All Around Landscape Supply or Aqua-Flo, can help homeowners
decide what technologies would be workable in their
situation. Additionally, S & S Seeds in Carpinteria
provides seed mixes of many native plants that can be sown in the
traditional manner or applied as a sticky liquid on difficult
slopes.