UC Davis Natural Reserve System
Stebbins Cold Canyon Reserve

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The Vegetation of Cold Canyon

Stebbins Cold Canyon Reserve provides an excellent opportunity to experience vegetation characteristic of the Inner Coast Ranges of North-Central California. Here, the variable California climate produces dramatic changes in vegetation, both in time and space. Over the course of the year, rain and temperature cycles force many plants to grow and reproduce during specific seasons. In addition, the relatively small area of Cold Canyon harbors a wide variety of plant communities, including grassland, savanna, chaparral, live oak woodland, and riverside (often called "riparian") vegetation.   These communities have a wealth of plant life, which you can access through a plant species list, as well as a blooming calendar of selected flowering plants.

Climate and its Effects on Plants.   Like countries surrounding the Mediterranean Sea, Northern California's climate is characterized by cool, wet winters, followed by harsh, dry summers. Therefore, the plants living in Cold Canyon must cope with the extremes of this so-called "Mediterranean" climate. In winter, the canyon often experiences freezing temperatures, and receives about half of its annual rainfall. The cool temperatures retard much plant growth, and most plants do not grow at all. By December, many trees have shed their leaves, and most other perennial plants have shut down their growth. A number of plants have extensive bulb or root systems that store nutrients during the winter. 

The situation is reversed in the summer, when summer temperatures soar above 100 F and less than 1% of the year's rain falls. In some respects, Cold Canyon is even harsher than other areas of the coast range. Nestled within the easternmost ridges of the North Coast Range, Cold Canyon receives somewhat less rain than hills to the west. These hills also prevent the drought-alleviating coastal fog from reaching Cold Canyon most of the summer.  

As a result, the plants of Cold Canyon are well-adapted to the drought conditions of the Mediterranean climate. Many annual plants avoid the harshness of summer simply by growing, reproducing, and dying entirely during the milder and wetter months. Therefore, many of the Cold Canyon's beautiful wildflowers are to be seen only in the spring. 

To survive through the summer drought, other plants live in cool "microclimates." The majority of species avoid drying out by growing in the moist and shady canyon bottom along Cold and Wildhorse Creeks. These areas are much cooler and moister than the average conditions of the reserve. Experience this microclimate simply by hiking to the location of the Cold Store. Even on a hot summer day, this spot is remarkably cool. Mild microclimates exist in wet areas, in shaded areas, and on north-facing slopes, while the harshest microclimates exist in rocky, bare, sunny areas on south-facing slopes.  

Perennial species that do not rely on riparian microclimates often have a number of adaptations that enable them to retain or gather moisture. Some plants found in Cold Canyon are "sclerophyllous," (from the Greek for "hard leaves"), and have small leathery leaves covered with a thick waxy coating that minimizes water loss. Other plants grow extremely deep root systems to find water. One such example is California's state grass, purple needlegrass (Nassella pulchra), which sometimes grows roots extending four meters into the soil. 

Plant Communities.  Because both mild and harsh microclimates exist in the reserve, and because different plant species are more or less tolerant of these microclimates, certain species tend to live in similar places. These groups of co-occurring species are known as plant communities. Plant communities are not easily defined, as many plants occur in different communities. Nonetheless, botanists have identified five or six general plant communities in Cold Canyon. These are termed grassland, savanna, chaparral, live oak woodland, and riparian woodland. These communities are described below.

Grassland . These areas are characterized by very little shrub or tree cover, and instead are covered by grass and other annual plants. Not surprisingly, grasslands are most frequently found on south-facing slopes, which are not readily colonized by brush and trees because of the harsh summer microclimate. Grasslands also occur in areas that have recently experienced a natural disturbance such as a fire or landslide. In these areas, the grasslands are more temporary, and will eventually be replaced by shrubs and trees.    Grassland communities of Cold Canyon have changed dramatically in the last few centuries. When European settlers came to California, they brought many new grasses and forbs (non-woody plants) with them, and these mostly annual exotic species now dominate the herbaceous vegetation of Stebbins Cold Canyon Reserve, particularly its grasslands.

Savanna . This association is characterized by scattered trees with an understory of grasses and forbs. Savannas exist in relatively dry microclimates; if more water were available, more trees would be able to grow, and the area would become a woodland. Therefore, the dominant trees of savannas can tolerate drought. Trees of Cold Canyon's savanna include the blue oak (Quercus douglasii) and the foothill pine (Pinus sabiniana).

Chaparral . Chaparral, comprised mainly of a dense mixture of shrubs that range in height from 3 to 9 feet, is the most common community type in Cold Canyon. In some places in Cold Canyon, the chaparral community is entirely dominated by chamise (Adenostoma fasciculatum), which produces a substance from its roots that appears to prevent many other plants from growing in the same soil. Other common chaparral shrubs of Cold Canyon include manzanita (Arctostaphylos manzanita), Scrub oak (Quercus berberidifolia), toyon or Christmas berry (Heteromeles arbutifolia), and buck brush (Ceanothus cuneatus).

Live oak woodland . In hillside areas where more water is available, live oak woodland predominates. This plant community is dominated by the interior live oak (Quercus wislizenii), the evergreen oak of Cold Canyon, but also includes foothill pine, blue oak, manzanita, buck brush, California coffee berry (Rhamnus californica) and buckeye (Aesculus californica).

Riparian woodland . The word "riparian," comes from the Latin word meaning river bank. Thus, riparian woodlands are the forests associated with streams and springs. These include trees associated with other communities, such as buckeye and interior live oak, as well as a number of less drought-tolerant species. Fremont cottonwood (Populus fremontii) and various willows (Salix spp.) grow right at water's edge, sometimes becoming surrounded by the creek as it shifts course due to landslides or torrential rainstorms. California bay (Umbellaria californica), with its aromatic leaves, and Western redbud (Cercis occidentalis), which shocks March visitors with its bright pinkish-red blossoms, are both scattered along the creek. Further up the path to the old homestead, look for the unusually shaped flowers of the spice-bush (Calycanthus occidentalis). Upon reaching the cold storage of the old homestead, take note of the tall trunks of the bigleaf maple (Acer macrophyllum).

Last Updated 03/09/06