Riparian Plant Community Classification
The topography, geology and climates of California vary throughout the state, and as a result California hosts a rich diversity of plant communities. Even within riparian areas of California, several plant communities exist. The richness of plant communities in riparian areas is in large part because plants respond to differences in the physical environment, such as hydraulic forces and soil textures. The ability of plants to establish, survive and grow is affected by the physical environment, which results in an uneven distribution of plant species. A plant community is an identifiable assemblage of plant species shaped by the interactions of individual plants with the environment and each other. Different plant communities are dominated by different tree, shrub or herbaceous species. Plant communities can be recognized as distinct from neighboring plant assemblages by the species composition. Plant communities may differ by the height of the tallest canopy layer, the number and density of canopy, shrub and understory layers, and by the variety of plant species that occur.
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Even though strict lines can rarely be drawn between plant communities, it is useful nonetheless to classify associations of plant species so that conservation and restoration targets can be communicated. For example, in order to conserve plant communities that are of high priority, it is necessary to sufficiently describe and locate them. Similarly, an understanding of the individual plant species that grow together in different plant communities helps guide restoration planting designs.
There are numerous ways to classify and describe these plant communities, and only a few are mentioned here. California Wildlife Habitat Relationships (CWHR) is an information source that provides broad descriptions of vegetation types throughout all of California. For example, the riparian communities that River Partners work with in the Central Valley include Valley Foothill Riparian, Valley Oak Woodland, and Freshwater Emergent Wetlands. Narrowing in focus from the CWHR classification, Sawyer and Keeler-Wolf (1995) developed a classification scheme that has been adopted by or is compatible with multiple conservation efforts in California. This classification system works by naming alliances of plant species by the dominant one to three plant species. This system is especially useful for identifying riparian communities from aerial photos that can be targeted for conservation, and monitored overtime.
River Partners restoration design is probably most influenced by the Holland (1986) classification of natural communities in California. The Holland classification places a strong emphasis on the ecology of the site, and brings attention to dominant tree, shrub and herbaceous species. The pool of possible species that River Partners can choose from to plant in their restoration sites is often identified from the following plant communities: Valley Oak Woodland, Mixed Riparian Forest, and Willow Scrub.
Valley oak woodlands, mixed riparian forests, and willow scrub are examples of terrestrial habitats that support wildlife such as insects, birds, amphibians, reptiles and mammals. These terrestrial habitats are very productive areas because of the abundance of plant material. Terrestrial plant communities act as sources of nutrients that support aquatic habitats as well. Aquatic wildlife such as fish and invertebrates directly benefit from the nutrients produced in terrestrial plant communities. Trees and shrubs that grow on the banks of the river create ideal habitat for many fish - Shaded Riverine Aquatic Habitat.