Santa Clara River Riparian Restoration Implementation in Santa Paula

The proposed project is a critical second phase of restoration for 250 acres of recovering mixed wetland riparian habitat on the Santa Clara River, approximately 3 miles east (upstream) from Santa Paula, California. This discrete stretch of the river is perennially moist and supports 0.5 – 1-mile-wide sections of complex and diverse riparian habitat. In 2018, a grant was awarded from the Wildlife Conservation Board to The Nature Conservancy for $3.9 million to remove the invasive bamboo-like grass arundo (Arundo donax) from the project area, encompassing several contiguous private properties of high ecological value, integrated riparian and wetland habitats. Project partners include The Nature Conservancy, University of California Santa Barbara, and Santa Clara River Conservancy.

For much of the site, arundo control occurred in areas where arundo occurred in scattered, smaller populations mixed with native riparian vegetation. These areas will more easily recover passively owing to the abundance of propagule sources from surrounding native species. However, approximately 85 acres of dense monotypic arundo was masticated across the project site and treated with herbicide, creating large, denuded open areas that are vulnerable to infestation by other invasive plants and potential type-conversion into non-native dominated zones with diminished ecological value. In addition, six miles of trails representing another 15 acres were created to facilitate access to distal project areas and smaller populations of arundo, creating linear paths of disturbance that are similarly vulnerable to invasive plant dominance. Invasive species commonly encountered on the site that are a risk to the recovery of these vulnerable disturbed areas include perennial pepperweed (Lepidium latifolium), thistles (Cirsium vulgare, Carduus pycenocephalus), short-pod mustard (Hirschfeldia incana), salt cedar (Tamarix spp.), castor bean (Ricinus communis), tree tobacco (Nicotiana glauca), and fennel (Foeniculum maculatum).

This second phase of restoration would build on the investment made to control arundo by restoring the highly impacted mastication areas and trail systems into diverse riparian habitats dominated by native species. Monitoring for and controlling invasive species within the target restoration areas will be a core, ongoing activity through the anticipated three-year project commitment. While mediating invasive species, active replanting to jumpstart structural and ecological function be the focus of the project, serving to provide competitive exclusion of invasive species and to supply localized propagules to recolonize the disturbed zones over time. The anticipated outcome of the project is to catalyze a biologically and structurally diverse riparian woodland that would have been present prior to arundo colonization with less than 10% absolute cover of invasive species and greater than 50% relative cover of native species.