Natural and un-natural plant communities of the Los Angeles River System
The Los Angeles River’s past as a seasonal river with springs, cienegas, and washes was substantially changed by a booming population that concentrated and constrained the river to concrete channels. Current project plans will begin to reverse this process and bring life again to this stormwater conveyance system.
The Los Angeles River watershed is 834 miles2 with river and tributaries that quickly become concrete after exiting canyons from surrounding mountains. Canyon tributaries contain willow, alder, and coast live oak riparian vegetation communities. These canyon habitats remain as potential source material for planned future restoration along and within the river system. The use of watershed-specific plant propagules is preferable to importing native plants from other areas of California.
The challenge with any river restoration in Los Angeles is balancing local genetic biodiversity, recreation, water conservation, and stormwater safety in a high density urban population area. Rights-of-way landscaping, isolated by concrete from the river’s water, have to rely on irrigation til plant establishment. These river-adjacent landscaping projects focus on highly drought-tolerant coastal sage scrub/chaparral species in their plant palettes.
Restoration plans within the river do not include concrete removal due to the proximity of a dense urban population and infrastructure. One such project is the Army Corps of Engineers’ Los Angeles River Ecosystem Restoration Study. The project’s objectives: to restore valley foothill riparian and freshwater habitat, to increase habitat connectivity, and to provide passive recreation. The challenge: what restoration can be accomplished within a river constrained by concrete that’s needed to protect lives and structures within the floodplain? The result may be a local vegetation community very different than existed historically.
In support of these projects, two years ago the Council for Watershed Health began a Native Seed Resources Coalition (NSRC) to focus stakeholders’ efforts to preserve local genetic biodiversity by increasing the supply of locally native plant species for restoration and landscaping projects. The NSRC comprises ecologists, horticulturists, land managers, landscape architects, engineers, planners, seed collectors, and native plant nurseries. The NSRC encourages cooperation on collection efforts to identify, collect, and store local seed in anticipation of these public projects. (http://nativeseed.watershedhealth.org)
As these projects move forward and as we struggle to balance significant issues, the Los Angeles River becomes an outdoor research laboratory in urban ecology in one of the most highly urbanized cities in the world.