Ecology of the Elfin Forest
The Elfin Forest supports diverse natural plant and animal communities because of its very special combination of geologic, soil, and climatic environments. Most of the habitats in the Natural Area pose both severe survival problems for plants and animals and also rare opportunities for species which are adapted to these environments. To see a map of the plant communities in the Forest click here.
A little over a quarter of the Elfin Forest lies in tidal lands of Morro Bay estuary. Plant species living in the marsh area are specially adapted to tolerate repeated flooding, drying, and varying degrees of salinity. Soil salinity rather than flood water salinity is the major determinant of what plants thrive in different parts of the marsh. Salinity is modified by fresh water coming down Los Osos and Chorro Creeks and springs at the base of the sand dunes. Where soil salinity is high the Coastal Salt Marsh Community is found – predominately Pickleweed and Saltgrass. Lower salinity yields the Brackish Water Marsh Community – dominated by rushes and sedges. The demarcation between salt and brackish water marsh is not clear cut. Contrary to what you might expect, the brackish marsh species are mostly seen in areas that flood twice daily, (adjacent to the base of the dunes and the springs) and the saltwater species are seen on higher marsh lands that floods less often (which concentrates the salt in the soil). Bordering the marshes, and above the high tide line, is the Riparian Woodland Community, where trees such as Sycamore and willows are able to survive because of fresh water coming to the surface.
Higher still are the old sand dunes, now stabilized by vegetation growing on them. The sand constituting these dunes is quite low in soil nutrients. It is also very coarse textured, which causes rainwater to sink rapidly downward, soon lost to plants with shallow surface roots. The coastal surfaces of the sand dunes are also directly exposed to winds off the ocean and estuary, which carry fine salt-laden mist onto the land. The salt-laden breezes, combined with nutrient-poor and dry soils, limit vegetation on the dunes closest to the estuary to the Coastal Dune Scrub Community. Plants of this community, such as the California sagebrush and Black sage, not only tolerate these conditions but thrive in the absence of the competition they would face in areas more favorable to a wider variety of species. Stunted by those salt-laden breezes and poor soils, the oaks of the Coastal Live Oak Woodland survive in the valleys sheltered behind the shoreline dunes and grow no taller than the crests of the dunes behind which they shelter. Farther inland and above the oak woodlands, on dry dune crests exposed to the sun and sea breezes is the Maritime Chaparral Community. This community is dominated by drought-tolerant and fire-prone shrubs such as Chamise and Buckbrush.
All plant communities tend to overlap and grade into one another where they meet. However, one area of overlap and mixing of species in the Elfin Forest covers such a broad area of the reserve and is so distinctive that it has quite rightly gained recognition as a local vegetation community on its own terms. This is known as the Oak/Manzanita Complex. This is basically an area of Maritime Chaparral somewhat protected by dunes from salt-laden breezes from the west and sloping away from the hottest afternoon rays of the sun. These protections have allowed groves of oaks to invade, becoming mixed with the chaparral. Also, manzanitas, ordinarily low bushes in the Maritime Chaparral, here have grown into tall and luxuriant groves. The species Morro manzanita has, in fact, evolved to fit this very special habitat along our coast, and is only found from Montaņa de Oro State Park through the Elfin Forest to Morro Bay State Park.
The dry climate of Los Osos contributes strongly to the environmental challenges facing the plant and animal communities of the Elfin Forest, but also provides some mitigating factors for species which can take advantage of them. Rainfall is low, little more than 16 inches a year on the average, and great variation from year to year can be devastating to most plants and animals. Most rain falls in the winter, usually from October through March. Lack of rain in the summers when temperatures are highest places great drought stress on species. However, the ocean influence mitigates this by producing temperatures both warmer in winter and cooler in summer than inland locations at the same latitude. This somewhat reduces the stress drought would otherwise cause for plants. Most Elfin Forest plants have adapted by growing vigorously in the mild, rainy winters and sunny spring, becoming dormant or nearly so in the warmer summers. The high humidity of the sea air reduces water losses by evaporation, and many plants have adapted to use moisture condensing from frequent fogs in otherwise dry summers. The isolation of this very special environment has encouraged rare plants and animals to find refuge here.