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San Francisco is a heavily urbanized city, which nonetheless has a rich variety of plant and animal communities. Among these are coastal scrub, grassland, oak woodlands, marsh, and stream-sides. Some of these habitats hold species found nowhere outside of California. The City also has landscaped areas designed to resemble plant communities not native to San Francisco, such as conifer plantings in Golden Gate Park. By providing food and shelter for migratory and resident birds, they too play a major role in supporting San Francisco’s biodiversity. Harvard professor and Pulitzer-prize winner Edward O. Wilson defines biodiversity as “the variety of organisms considered at all levels, from genetic variants belonging to the same species through arrays of species to arrays of genera, families, and still higher...levels [of organization].” A sustainability plan for maintaining biodiversity must address genetic diversity, the number and variety of species in the City, the variety and quality of the City’s ecosystems, and the ecological and evolutionary processes that sustain biodiversity. Even in the increasingly urbanized San Francisco environment, there are four primary reasons why protecting and maintaining biodiversity are important. As expressed by Wilson: Biodiversity maintains the integrity of life known on earth; Through medicine, agriculture and economics, biodiversity provides a range of genetic, biochemical, and physical properties of plant and animal life that are advantageous to human welfare; Biodiversity is worthy of preservation because it represents human kinship through common living organisms; and Biodiversity is a source of national heritage, giving historic importance to place, such as the San Francisco bioregion with its distinctive assemblage of species of plants and animals.

Past and present threats to biodiversity include the introduction of non-native plants that displace indigenous plants; features of urban development that have resulted in loss and fragmentation of habitat; mismanagement of domesticated animals (past grazing practices decimated native grass species and irresponsible pet ownership seriously disturbs habitat integrity); and, more generally, the negative effects of industrial pollution on air, water, and soil. San Francisco cannot turn back the clock and return to its pre-urban environment, but the City can take actions to preserve its remaining biodiversity and restore some of what has been lost. Fundamental to this mission is promoting public understanding of the City’s local plants and animals, and managing San Francisco’s natural and landscaped habitats in a way that enhances the City’s biodiversity. The strategy for preserving biodiversity is presented in the following matrix. Terms that appear in quotes are defined in the definitions section, as are several terms that have appeared in this introduction.

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