Museum of Riverside

Museum of Riverside

Plant Communities of Riverside County

Plant Communities conveniently puts a name to geographical areas and the plant species we commonly associate with them. Over thousands of years, both the landscape and the plants upon it have slowly evolved together, so that those plant species with the best record of survival in a specific setting have usually become the most prominent identifying characteristics of that setting. Because plant life in some form seems to exist throughout the Earth's land areas, we cannot avoid identifying a place without knowing its most conspicuous plant species. While these conspicuously successful plants have served to shape the environment, they have also created a setting that favors an array of associated plant species. These dominant plants and their associated species make up natural plant communities.

Riverside County possesses a remarkable diversity of plants and plant communities. This is in large part due to the extremes of weather and topography that range across its length, from east to west. One way to become familiar with the geography of this large county, and ultimately with its natural and cultural history, is to become familiar with the distribution of these plant communities.


Information for the online exhibit was derived from the following resources: Hickman, James C., ed. (1993) The Jepson Manual: Higher Plants of California. Univ. of Calif. Press Munz, Philip A. and David D. Keck (1968) A California Flora and Supplement. Univ. of Calif. Press Munz, Philip A. (1974) A Flora of Southern California. Univ. of Calif. Press Ornduff, Robert (1974) Introduction to California Plant Life. Univ. of Calif. Press Vasek, Frank C. (1982) A Vegetative Guide to the Perennial Plants of Southern California. San Bernardino Co. Museum

Plant Communities Legend

Coastal Sage Annual rainfall: 10 to 20 inches
Found on southwest-facing slopes below 3000 feet, sage scrub plants frequently drop their leaves and appear withered during dry seasons. Sage and other scrub species can be fragrant; they secrete oily chemicals as part of a process that aids them in the competition for soil, space and water.
Chaparral Annual rainfall: 15 to 25 inches
Chaparral communities grow on slopes between 1000 and 5000 feet in elevation. Chaparral is characterized by dense shrubs and small trees sometimes called an "elfin forest". Dense root crowns formed by chaparral plants resist erosion and aid regrowth after recurring fires. The foliage of these plants is characteristically evergreen, with glossy coatings and oily resins that increase drought resistance. Wildflowers and other low annuals are more conspicuous in open, recently burned areas.
Southern Oak Woodland Annual rainfall: 15 to 25 inches
Mountain foothills and plateaus will often support mixed stands of live oak trees and other hardwoods, usually with grasses growing beneath them. When found in canyons and on north-facing slopes, the oak woodlands may be mingled with chaparral vegetation, with chaparral plants being dominant in more open areas and on south-facing slopes.
Southern Yellow Pine Forest Annual rainfall: 30 to 50 inches
Ponderosa and Jeffrey pine trees are the dominant plants of local mountain forests, between elevations of 5000 to 9000 feet. The open, park-like habitats created by these trees encourage growth of shrubs as well as annual and perennial wildflowers.
Joshua Tree Woodland/ Mojave Pine Scrub Annual rainfall: 6 to 15 inches
Lying between elevations of 2000 and 600 feet, this region experiences more rainfall and cooler temperatures on average than the Colorado Desert communities.
While not technically "trees", the distinctive yuccas - known as "Joshua Trees" - may grow to considerable size (up to 30 feet) and are assumed to live for a century or more. Small junipers and pines, and large shrubs mingle with the Joshua Trees at the higher elevations, giving way to cactus and creosote bush scrub at lower levels.
Pinyon-Juniper Woodland Annual rainfall: 8 to 15 inches
This distinctive community is generally found at the lowest (4000 to 7000 feet) forested elevations of the eastern mountain slopes. The trees are scattered and not very tall, and are often intermingled with sagebrush and other scrub.
Subalpine Forest Annual rainfall: 35 to 50 inches
Above 8000 feet, local mountain forests change to include more durable, cold-hardy, slow growing species, such as Limber and Lodge pole pines. Trees are more scattered than in the Yellow Pine Forest, allowing for more growth of colorful, low growing shrubs and wildflowers.
Saltbush Annual rainfall: less than 2 inches
These communities are characterized by poor drainage (often found below sea level), producing an accumulation of soil salts and alkaline substances, sometimes seeping in from adjacent salt lakes. Only those plant species survive that are adapted to such salty and caustic conditions.
Colorado Desert Communities
Perennial Scrub,

Annual rainfall: less than 8 inches
The vast, gently sloping plains of eastern Riverside County experience some of the world's most extreme desert conditions. Plants here survive the harsh sunlight, high winds and lack of rainfall through a combination of sheer endurance and remarkable physical adaptations. Various species are able to store rain water, reach deep into the earth for ground water, or compete for water by dominating their growing space.
Washes Though they appear dry much of the time, the deep sandy soils of these stream beds store water from wetter seasons. Certain deep-rooted plant species may thrive here, with occasional floods serving to disperse seeds down the length of the wash, where they may lodge in soil trapped between boulders.
Ephemeral Herbs Ephemeral Herbs lack woody structures, and thus when dormant may appear to die back right to ground level. "Ephemeral" describes the transitory qualities of these desert herbs, which may comprise as much as 50% of the region's desert plant diversity. Many of these species sprout from seed and flower only during the occasional wet season (either winter rains or summer storms), the intervals between which may last years. For only a few weeks, desert habitats will be awash in bright colors, as these plants bloom and produce seeds, which eventually come to lie dormant in the desert soil.
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