Restoring the Riparian Forests of the Sacramento River
Sacramento River Conservation Area Handbook
Anyone walking from a grassland or open field into a riparian area along the Sacramento River during a hot summer day is acutely aware of the abrupt change in habitat. Not only is the area cooler because of a dense closed canopy but the air is humid due to high transpiration rates of the surrounding trees. Grass and annual species, which dried up weeks or months ago in the adjacent lands, remain green and succulent under the numerous layers of riparian vegetation.
When viewed from the surrounding foothills, the riparian forests of the Sacramento River may appear as a uniform blanket of lush green growth. A closer view, however, reveals distinct bands of vegetation, differentiated by plant species composition, forest structure and wildlife usage. The Sacramento River system is actually composed of a wide variety of habitat types. These habitat types include the successional stages of the riparian forest, gravel bars and bare cut banks, shady vegetated banks, and sheltered wetlands such as sloughs, side channels, and oxbow lakes. This diversity is key to the wildlife habitat value of the Sacramento River system
The Sacramento is the most important river in California. Its riparian corridor is an oasis in the otherwise dry Mediterranean climate of the Central Valley. The Sacramento River and the riparian corridor it supports provide a habitat for wildlife that is of national significance. It not only produces most of the salmon caught in California, it also produces most of the salmon caught off the coast of Oregon. In addition to the salmon and steelhead fisheries that most folks are familiar with, the river provides habitat for 250 species of mammals, amphibians, reptiles, and birds including 65 species of special concern (status unknown or precarious) and 33 threatened, endangered, extinct, or extirpated species.
Historically, the Sacramento River was bordered by up to 500,000 acres of riparian forest, with valley oak woodland covering the higher river terraces. Rapid development of the Sacramento Valley began in the second half of the 19th century. By 1868 some noticed a scarcity of woody vegetation. Use of trees for lumber and fuel, particularly cordwood for steamboats, reduced the extent of the riparian forests in the Sacramento Valley. Since then urbanization and agricultural conversion have been primary factors eliminating riparian habitat. Water development projects, including channelization, dam and levee construction, bank protection, and streamflow regulation have altered the riparian system and contributed to vegetation loss. Approximately 25,000 acres of riparian habitat and valley oak woodland remain within the Sacramento River corridor from Shasta Dam to its confluence with the Feather River.
In a large alluvial river like the Sacramento, the riparian forest is created in the wake of the river meandering across its floodplain. Channel movement is often incremental and the river bends gradually move downstream. The channel will repeatedly move back and forth along a meandering river reworking much of the same area. This area is refereed to as a meanderbelt. In areas
where the river is actively meandering, it is the downstream movement of these river loops that define the minimum width necessary to maintain the continuum of riparian plant communities and habitats created by the river over time
Meandering is to the Sacramento River what fire is to its upland forest ? a basic ecological process necessary to perpetuate ecosystem health. The fundamental question is: How can we as a society coexist with dynamic processes that are the foundation of landscape scale ecosystems? Where is the balancing point? How often does the forest need to burn? How much space does a river need?
Given adequate flow and room to meander the river will regenerate its shadowing riparian forest and the diversity of habitat types indicative of a healthy system. Although restoration of the riparian forest through active cultivation is important, in many places along the Sacramento River it is the preservation and re-establishment of dynamic physical processes that is key to a sustainable, healthy ecosystem. It is estimated that 30,000 acres of frequently flooded land is needed to sustain a viable riparian ecosystem in the roughly 100 river miles between Red Bluff and Colusa.
We cannot replace or recreate the beneficial effects of river meandering -- the erosion/deposition cycle that drives biological succession of riparian forests, replenishes and recycles spawning gravel, and renews and maintains habitat for aquatic and terrestrial species on a landscape scale. And yet, this natural process must be balanced against beneficial human uses/needs.
Recognizing that the Sacramento River is both a natural and a cultural system, the Sacramento River Advisory Council (created by Senate Bill 1086, in 1986) and, more recently, the Sacramento River Conservation Area Forum are working to ensure that habitat management along the Sacramento River addresses both the dynamics of riparian ecosystems as well as the realities of local government, agricultural, landowner and stakeholder issues.