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TREES and SHRUBS OF CALIFORNIACALIFORNIA NATURAL HISTORY GUIDES
By JOHN D. STUART JOHN D. SAWYER
University of CaliforniaCopyright © 2001 Regents of the University of California
All right reserved.
IntroductionHOW THE BOOK IS ORGANIZED
Conifers and broadleaved trees and shrubs are treated separately in this book. Each group has its own set of keys to genera and species, as well as plant descriptions. Plant descriptions are organized alphabetically by genus and then by species. In a few cases, we have included separate subspecies or varieties. Genera in which we include more than one species have short generic descriptions and species keys. Detailed species descriptions follow the generic descriptions. A species description includes growth habit, distinctive characteristics, habitat, range (including a map), and remarks. Most species descriptions have an illustration showing leaves and either cones, flowers, or fruits. Illustrations were drawn from fresh specimens with the intent of showing diagnostic characteristics. Plant rarity is based on rankings derived from the California Native Plant Society and federal and state lists (Skinner and Pavlik 1994).
Two lists are presented in the appendixes. The first is a list of species grouped by distinctive morphological features. The second is a checklist of trees and shrubs indexed alphabetically by family, genus, species, and common name.
To classify is a natural human trait. It is our nature to place objects into similar groups and to place those groups into a hierarchy. Biologists group plants by morphological and genetic characteristics. An example of a widely accepted taxonomic hierarchy is found in Table 1. This is not a static classification, and modifications are proposed based on new morphological and genetic information.
Taxonomists often use intermediate ranks such as tribe or subgenus to organize complexity in large families and genera. Our book has occasional references to ranks below genus. The classification of lodgepole pine (see Table 2) serves as a good example of ranks below genus.
The rules and procedures for naming plants can be found in The International Code of Botanical Nomenclature (Greuter and others 1994). The valid code is based in part on the principles that names reflect the earliest published description, that there can be only one correct name for a plant, and that scientific names are in Latin.
Species names are made up of two parts, the genus name and the species epithet. It is incorrect to use only the species epithet, since little information is gained from it alone. The species epithet menziesii, for example, is used for Douglas-fir (Pseudotsuga menziesii) and Pacific madrone (Arbutus menziesii). The genus name and species epithet are normally italicized or underlined. The first letter of the genus is always capitalized and the epithet, subspecies, and variety names are lowercased irrespective of source. Roman type is used when writing the names of all ranks higher than genus, the author's name (i.e., the name of the botanist who first formally described the plant), and the abbreviations for subspecies (ssp. or subsp.) and variety (var.). When writing about a species, it is a convention to abbreviate that species' name after the first instance, giving the first initial of the genus name rather than rewriting the entire name, as long as the discussion includes no other genus that begins with the same first letter. The plural of species is species and the plural of genus is genera. Species and specific are appropriate adjective forms for species, and generic is the appropriate form for genus.
Plants are occasionally reclassified and renamed based on new interpretations of genetic and morphological evidence. Most changes are proposed for the ranks genus, species, and subspecies, but not all proposed changes become widely accepted. When you are in doubt about the proper name for a plant, we recommend that that you consult the most recent, authoritative book on regional flora.
Common names have fewer rules and conventions than scientific names have. They differ from scientific names in the following ways: they are often the only names known by many people; they are familiar in only one language; a species can have more than one common name (for example, California bay, Oregon myrtle, pepperwood, California laurel, and a few other names all refer to one species); and more than one species or genus can have the same common name (for example, sage). Rules for common names include lowercasing all words except for proper names (for example, sugar pine versus Torrey pine) and hyphenating names or making them into one word if the object is not "true" (for example, Douglas-fir is not a member of Abies, the firs, and western redcedar is not a member of Cedrus, the cedars). As with scientific names, when you are in doubt about the common name, consult the most recent, authoritative book on regional flora. Organizations such as the U.S. Forest Service maintain lists of preferred common names.
HOW TO USE THE BOOK TO IDENTIFY TREES AND SHRUBS
Identifying plants from a guidebook usually entails a set of sequential steps. We recommend that the following procedures be adopted when using this book.
1. Determine whether the unknown specimen is a conifer or broadleaved plant and then turn to the appropriate key.
2. Address questions of growth habit before you begin the keying process:
a. Is it a tree or a shrub? Little (1979) defined trees as woody plants "having one erect perennial stem or trunk at least 3 inches (7.5 centimeters) in diameter at breast height (4 1/2 feet or 1.3 meters), a more or less definitely formed crown of foliage, and a height of at least 13 feet (4 meters)." Shrubs, in contrast, are smaller and generally multistemmed.
b. Is it erect or prostrate?
c. How tall is it?
d. Does it have multiple stems?
3. Use the key to identify the genus of your plant. Work your way through the key by selecting between sequential pairs (couplets) of alternately indented opposing statements (dichotomies). The couplets describe a small set of the plant's morphological characteristics, and occasionally geographical or habitat characteristics are included. Choose the statement that best fits your plant. If the statement ends with a name, find the genus in the alphabetically arranged pages. If the statement does not end with a name, go to the next indented pair of statements and continue the process until you eventually arrive at a name.
4. Read the description of the genus to ensure that it fits your plant.
5. Next, use the species key in the same manner in order to identify the species. Genera in which we present only one California species do not have a species key.
6. Read the species description to be sure it fits your plant. In addition to the species' morphological characteristics, pay close attention to its growth habit, habitat, and range. References to largest individuals are included in some species descriptions. Largest individuals are determined using a combination of height, circumference, and crown spread (Cannon 1998). Diameters refer to trunks. The largest plant, therefore, is not necessarily the tallest.
7. Check to see if the habitat and range described in the book match the habitat and range of your plant. We use the terms coastal, low-elevation, foothill, montane, subalpine, and alpine to further define a species' habitat.
The shaded parts of each range map correspond to the ecological regions in which the plant grows (Map 1) (Goudey and Smith 1994). This does not imply, however, that the plant grows everywhere inside the shaded areas. Combine the habitat description with the elevation range to better define the plant's natural range.
CALIFORNIA'S FORESTS AND WOODLANDS
Most of California's landscapes have characteristic trees and shrubs. The north coast, for example, is home to redwood and Douglas-fir forests; the central coast has isolated stands of Monterey cypress and Monterey pine; the Sierra Nevada is noted for its mixed conifer forests; southern California has extensive chaparral stands; desert regions are noted for Joshua trees, junipers, and pinyons; and the Central Valley is surrounded by foothills with blue oak woodlands.
Tree-dominated vegetation can be called either a forest or woodland. Forests typically have trees close enough that their crowns touch. Not all crowns, however, touch or overlap, as forests usually have large gaps in their canopies. The older the forest, generally speaking, the larger the gaps. Some forests have gaps amounting to as much as 75 to 80 percent of the area. Woodlands, in contrast, have widely spaced trees with grass or shrubs among them. In general, forests have more than 20 percent canopy cover, while woodlands have less than 20 percent canopy cover.
Shrub-dominated areas have various names. Chaparral is a name used for shrublands composed of species with thickened, evergreen, leathery, sclerophyllous leaves. Scrub is a term applied to shrublands that have either widely scattered or drought-deciduous shrubs (e.g., southern California's coastal scrub). Occasionally, shrub types are named after a commonly occurring shrub species, such as big sagebrush in the Great Basin.
Forests and woodlands vary greatly throughout the state. Oaks dominate in many of the state's lower-elevation forests and woodlands, while conifers are generally more common on mid-and high-elevation mountains as well as in low-elevation coastal forests. In some areas, conifer forests and woodlands are distinct from those dominated by broadleaved trees. In other areas there is considerable mixing of conifers and broadleaved trees, as is the case with the so-called mixed evergreen forests.
The state's vegetation diversity is largely a function of varying climates, landforms, geological formations, and soils. Even though these factors vary continuously across landscapes, it is possible to characterize regions within the state as having similar ecological attributes. The Mojave Desert's vegetation, climate, landforms, geological formations, and soils are quite different from those found in, for example, the Klamath Mountains. Some tree and shrub species are found exclusively in a single ecological region (e.g., Torrey pine and Sadler oak), while others can be found in many regions (e.g., canyon live oak and wedgeleaf ceanothus). Knowing the ecological region(s) in which a plant grows is useful for identification and for understanding ecological requirements.
Increasingly, ecologists, botanists, natural resource professionals, geologists, and geographers characterize California's ecosystems (Bailey 1995), flora (Hickman 1993), and vegetation (Sawyer and Keeler-Wolf 1995) on the basis of region. The 20 ecological sections (see Map 1) we recognize are adapted from those described by Miles and Goudey in their book Ecological Subregions of California: Section and Subsection Descriptions (1997). For a detailed description of California's vegetation, refer to Barbour and Billings (1988), Barbour and Major (1988), Holland and Keil (1995), and Sawyer and Keeler-Wolf (1995). The ecological subregions of California described by Miles and Goudey (1997) are based on the National Hierarchical Framework of Ecological Units (McNab and Avers 1994) and Bailey's Description of the Ecoregions of the United States (1995). ECOMAP (1993), which is a companion to Ecological Subregions of California, maps California using this classification.
The hierarchical levels of the national framework of ecoregions are domain, division, province, section, and subsection. Large climatic zones define domains and divisions, and broadscale natural vegetation types define provinces. Sections and subsections are further delimited based on landforms, soils, local climates, and vegetation. California, for example, is divided into the humid temperate domain, characteristic of most of the state, and the dry domain, associated with the deserts. California's humid temperate domain has the Mediterranean division and the Mediterranean regime mountains division. California's dry domain is made up of the tropical/subtropical desert division and the temperate desert division (see Table 3).
HUMID TEMPERATE DOMAIN
The Pacific Ocean greatly moderates the climate of the coastal regions and, to a lesser extent, of the inland valleys. Winters are moderate and typically rainy, while summers are warm to hot and dry.
CALIFORNIA COASTAL CHAPARRAL FOREST AND SHRUB PROVINCE
Central Coast Section This section extends from San Francisco Bay to San Luis Obispo Bay. Prominent landmarks include Mount Diablo, the San Francisco Peninsula, Santa Cruz Mountains, Salinas Valley, and Santa Lucia Mountains. Mountaintops typically vary between 450 m (1,500 ft) and 1,200 m (4,000 ft) in elevation. Annual precipitation ranges from 30 cm (12 in.) to 150 cm (60 in.). Summer and winter temperatures are moderate. Coastal slopes are covered with redwood forests or coast live oak and mixed oak woodlands. Blue oak and valley oak woodlands are more evident inland. Much of the ocean-facing and inland, low-elevation slopes are covered with chaparrals made up of ceanothus, chamise, and manzanita. At higher elevations, canyon live oak is common and stands of Coulter pine suggest the beginning of a montane zone on the highest peaks.
South Coast Section This section extends from Point Sal to San Diego. Prominent landmarks include the Santa Ynez Mountains, Santa Susana Mountains, Santa Monica Mountains, Channel Islands, Los Angeles Basin, and San Diego Bay. Elevations range from sea level to around 1,000 m (3,000 ft), and annual precipitation varies between 25 cm (10 in.) and 75 cm (30 in.). Summer temperatures are moderate to warm, while winters are moderate. The South Coast Section characteristically has woodlands of California walnut, coast live oak, and/or Engelmann oak punctuating slopes of coastal scrubs, chaparrals, and grasslands. Coastal scrubs, once extensive, are shrublands consisting of black sage, California buckwheat, California encelia, California sagebrush, and white sage. Chaparral is the most extensive shrubland type in southern California, and it varies greatly in species composition. Many slopes are covered with monotonous expanses of chamise or scrub oak, but others are covered by a mixture of shrubs, including many species of ceanothus, manzanita, and oaks. Bigcone Douglas-fir is found on steep north slopes.
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