Plant Community: An assemblage or association of certain dominant indicator species occupying a given region. In California the desert biome consists of several different plant communities, such as the creosote bush scrub, shadscale scrub, sagebrush scrub, Joshua tree woodland and pinyon-juniper woodland. The local chaparral and coastal sage scrub plant communities surrounding Palomar College are condidered part of an arid desert biome. Some general biology textbooks have added a seventh biome called the "shrubland biome" to encompass these brushy habitats.

Chaparral: A plant community composed of dense, impenetrable, shrubby vegetation adapted to a Mediterranean climate with winter-wet and summer-dry seasons. The plant community is well-developed in the mountains of San Diego County. Following periodic brush fires, many of the shrub species resprout from subterranean lignotubers.

Coastal Sage Scrub: A plant community similar to the chaparral, but typically found at lower elevations (generally below 2,000 feet). It is dominated by aromatic coastal sagebrush (Artemisia californica) and black sage (Salvia mellifera), and is common in the hills bordering Palomar College. Unfortunately, this plant community is prime land for developers and is rapidly being replaced by housing developments in San Diego County. It is now (2001) considered to be an endangered (threatened) plant community in southern California.

Shrubs of the coastal sage scrub are adapted to the long, dry summers in several ways. Remaining dormant throughout the dry season, they may lose 80% of their water. During this time they may drop many of their brittle, shriveled leaves or produce smaller leaves on secondary shoots. Root systems are generally shallow because the plants are inactive much of the time. It is relatively easy to clear away desiccated shrubs with a heavy hoe during the summer drought season, compared with well-anchored shrubs of true chaparral. The oily, resinous leaves also help to conserve vital moisture, but increase their flammability. The dominant shrubs are fire adapted with seeds that readily germinate after fire. This also includes numerous species of post burn wildflowers that bloom in profusion following the winter and spring rains. Unlike scattered laurel sumac (Malosma laurina) and lemonade berry (Rhus integrifolia), the dominant semi-woody shrubs (mostly Artemisia, Salvia, & Eriogonum) lack lignotubers and rely on seeds for regeneration after fire. These shrubs are vulnerable to excessive or poorly-timed fires, particularly when competing with naturalized grasses and other weedy species. The common vine throughout the coastal sage scrub called wild cucumber (Marah macrocarpus) sprouts soon after fires from a large, subterranean caudex. Under ideal natural conditions, complete recovery of coastal sage scrub after a fire is about 15 to 20 years.

Ecosystem: All of the organisms in a natural community or biome plus all of the associated environmental factors with which they interact. The term ecosystem could actually be applied to any of the terrestrial biomes or plant communities. For example, the tundra biome could also be referred to as tundra ecosystem; the chaparral plant community could also be referred to as the chaparral ecosystem. The term ecosystem is well-suited for aquatic communities such as ponds, lakes, streams and even the ocean. In fact, oceanography is the study of the ocean ecosystem. Including ocean, topsoil and atmosphere, the earth is a large, complex ecosystem called the biosphere; however, in terms of the vast universe it is but a mere dot. A self-contained spaceship in which gasses and waste are recycled may also be thought of as an ecosystem.

Biosphere: (Earth Ecosystem): The zone of atmosphere, land and water at the surface of the earth occupied by living things. In grave danger by the effects of humans, including overpopulation, pollution and exploitation.

Environment: The sum total of physical and biotic factors that surround an organism or population of organisms.