National Wildlife Federation/ San Diego County

Ecological Zones of San Diego County

by Sandy Yayanos, Habitat Steward

Traveling east from the coast to the Imperial County offers a chance to explore the diverse ecological zones of San Diego County. The coastal terraces and mountains that separate the coast from the desert produce a rain shadow that helps to create this dramatic diversity. Rainfall and temperature can vary considerably from west to east. Our westerly winds are packed with moisture from the ocean. This moisture helps minimize the coastal temperature fluctuation. Then when this moisture laden air hits mountains of the Peninsular Range it rises and cools, causing the moisture to fall as precipitation. On the leeward side of the mountains the air is now devoid of moisture creating desert conditions.

More than 6,700 species of plants and animals have been identified in the diverse habitats of the county and many of these are endemic species. As a result we have more species at risk of extinction than elsewhere in the continental United States.

There are 10 major plant communities in the county with one often blending into another. Some are quite intact and others have almost disappeared from urbanization. All have the presence of alien species.

COSTAL SAND DUNE COMMUNITIES
Unfortunately, very little of this habitat is still found on our coast having been replaced by urban development. Pockets around the protected areas of lagoons have sand verbena (Abronia umbellate) and salt bush (Atriplex lentiformis). Small leaves, low spreading growth and salt tolerance characterize most of these plants.

SALT MARSHES AND MUDFLATS
This is a favorite area of bird watchers and hikers as there is usually a lot of wildlife to observe. San Diego has recorded over 475 species of birds with over 319 of these species in and around the lagoons. California is on the Pacific Flyway so many of these birds are just passing through or are part time residents. An array of food is found in the water (both fresh and salt), mudflats and the drier areas around the marshes. Under the water is a nursery for many fishes and invertebrates. This is one of the most endangered habitats in the world.

A constant change in water levels may stress plants and animals from fluctuation in salt and oxygen concentrations, and temperature. Many plants are salt tolerant (halophytes). Species commonly found are pickle weed (Salicornia sps.) salt grass (Distichlis spicata), alkali heath (Frankenia galena), sea lavender (Limonium californicum), salty susan (Jaumea carnosa) and shore grass ( Monanthochloe littoralis).

This habitat needs to be visited monthly and at high and low tide to see the tremendous change in bird populations.

COASTAL SAGE SCRUB
Ascend the marine terraces especially on the south and tops and notice that the soil has a little more organic matter and the wind has somewhat abated, but it is still semi arid. Plants are modified to survive high light intensity and low moisture. Small gray-green leaves, waxy coatings (cutin), leaf curling are common adaptations. With just 10-20 inches of rainfall mainly in winter many plants are drought deciduous which means the leaves are dropped during dry spells or during our summer months. Black sage (Salvia mellifera), sagebrush (Artemisia californica), flat top buckwheat (Eriogonum fasciculatum), coyote bush (Baccharis pilularis), laurel sumac (Malosma laurina) and bush sunflower (Encelia californica) are good indicator species of the coast sage scrub also called soft chaparral.

CHAPARRAL
Chaparral is found on north slopes near the coast and inland to about 4000 feet and where rainfall is from 14-25 inches. The leaves of plants are broader, the stems or trunks are woody and the plants grow taller. Chaparral can be difficult to walk through in undisturbed areas but it is quite rich in wildlife. Roots of some of these plants can be incredibly deep to tap moisture from winter rains. The plant adaptations seen in sage scrub can also be found here. Indicator species include manzanita (Arctostaphlos and Xylococcus sps.) California lilac (Ceanothus sps.) toyon (Heteromeles arbutifolia), lemonade berry and sugar bush (Rhus intregrifolia and R. ovata), scrub oak (Quercus dumosa). Many plants in the chaparral need fire to reproduce.

RIPARIAN
Water sheds or the drainage areas between hills and mountains will often have intermittent streams or rivers. Since ground water is close to the surface, larger trees like western sycamore (Platanus racemosa), willows (Salix sps.), and Fremont cottonwood (Populus fremontii), Mexican elderberry (Sambucus mexicana) are found. Mule fat (Baccharis glutinosa), cattails (Typha sp.) and spiny rushes (Juncus acutus) flourish around the edges of water. Birds, mammals, reptiles, and insects abound in these areas.

OAK WOODLANDS
Foothills and valleys above 3,500 feet may host 20-60 foot oak trees mainly live and Engelmann oaks (Quercus agrifolia and Q. engelmannii). These are generally mild winter areas with 15-25 inches of rain but with summers warmer than at the coast. Ground water is usually available for the trees to tap.

VALLEY GRASSLANDS
Where the soil is deep and more porous ground water becomes unavailable to trees. This results in our grasslands. Unfortunately many of the native grasses have been replaced with introduced species. Look for grasslands to be interspersed in areas around the oak woodlands.

YELLOW PINE FOREST
Above 4,000 feet the growing season is shorter but the yearly precipitation increases to 30-47 inches. Snow can briefly blanket the area in winter and summers are quite mild from 75-85 degrees. Trees may reach 100 feet and include pines (Pinus coulteri, P. jeffreyi, P. ponderosa), black oak (Quercus kelloggii) and big cone spruce (Pseudotsuga macrocarpa). Deer, mountain lions and bobcats still roam the area. Look for woodpeckers.

JUNIPER SCRUB
As the mountains are crossed the yearly rainfall diminishes and temperatures rise, thus the plant size is reduced. Indicator species include California juniper (Juniperus californica), scrub oak (Quercus turbinella) and pinyon pines (Pinus quadrifolia and P.monophylla). This area is also referred to as a hot steppe.

DESERT
This desert is hot during the day and cold at night and with less than 10 inches of rain a year. Soil is poor in organic material. Many plants are widely spaced appearing to be uniformly planted. But competition for water and the production of allopathic chemicals by many plants keep plants from close contact. Of course expect to see cacti but also creosote bush (Larrea tridentata), Ocotillo (Forequieria splendens), brittle bush (Encelia farinosa) and desert agave (Agave deserti) are very common. Winter rains if sufficient can produce a wild flower show not to be missed. Look for bighorn sheep.