Santa Clara River Restoration
History & Overview
The Santa Clara River watershed is an 83 mile (134 km) long river that spans both Ventura and Los Angeles Counties in Southern California. The river drains an extensive and biologically rich region at the junction of five of California’s 10 identified Bioregions, and contains a particularly strong representation of the biodiversity in the South and Central Coast Bioregions. The river is the last major coastal system in southern California that retains much of its natural hydrology and still provides the ecosystem functions necessary to sustain more than 17 federally listed species. The river system provides critical habitat and landscape linkages between these bioregions, including the Sierra Madre and Santa Felicia mountains to the north and Santa Susana-Simi Hills and Santa Monica Mountains to the south. The river basin also supports some of the most valuable agricultural resources in the world, as well as water resources for surrounding urban populations. Although the SCR contains extensive natural areas, it was identified as a critically endangered river by American Rivers in 2005 because of urban development and other threats in the region. The river drains parts of the Transverse Range system located in Southern California, and is less modified in comparison to other remaining water systems in California. In terms of Human use, much of the Santa Clara River Valley is used as agricultural land, due to the flat the rich and fertile floodplains that flank the river. The significance of the Santa Clara river to both humans alongside its many other species is why RIVRLAB diligently works to maintain the sustainability of the river.
Greater Scope
The significance of the Santa Clara river extend past that of just the region as well. As a whole, riparian species in California are struggling due to the vast amount of environmental changes that have occurred over the past century. Due to the influx of population to California, over 95% of all Southern California’s wetlands and rivers have been destroyed, with the only remnants being dirty concrete rivers that run through cities. As a result, many of California’s native flora and fauna have been classified as endangered. Southern California, which is already an arid habitat, has very few rivers that remain as untouched as the Santa Clara, further emphasizing the importance of restoration attempts.
Invasive Threats
One of the largest threats to the ecology of the Santa Clara River are the multitude of invasive species that have managed to find a home in th efertile lands around the river. Invasive plan species have led to the endangered status of a large portion of the native flora that exist in the river valley. Of these invasive species, Arundo donax has seen the largest growth in the region due to its ideal growing habitat for the invasive grass. This large grass, native to Eurasia, has been classified as a noxious weed by the state of California and the California Invasive Plant Council lists it among the top five invasive species degrading natural ecosystems in the state (Cal-IPC 2006). The effects of Arundo donax have already been seen to a great extent in the Santa Clara River, where it has outcompeted native species, reduces habitat value, and alters fire and flood regimes (Lambert et al. 2010). Other invasive plant species impacting the project area include tamarisk (Tamarix spp.), castor bean (Ricinus communis), perennial pepperweed (Lepidium latifolium), and exotic annual forbs. Invasive African clawed (Xenopus laevis) and bullfrogs (Rana catesbeiana) are abundant in standing water habitats in the project area where they prey on native frog and fish species, leading to declines in several sensitive species (Peek 2006). Research by UCSB scientists aims to understand the ecological impacts of invasive species on the river system and develop strategies for reducing these impacts while promoting the recovery of sensitive and endangered native species.
Human Intervention
In addition to invasive species altering the ecosystem, human intervention in the Santa Clara River have led to variety of issues as well. The RIVRLab’s project area is located in Santa Paula and Fillmore (Ventura County) between the confluences of Sespe and Santa Paula Creeks. The riparian corridor in this reach historically known as East Grove is up to ¾ mile wide and supports perennial flows, artesian springs, riparian forests, marshes, ponds, and other diverse wetland habitats. Human encroachment into and modification of the flood plain and riparian habitat have altered the ecosystem properties of the watershed, leading to riparian and aquatic habitat loss and degradation (Stillwater Sciences 2008). Manipulation of water resources has caused severe impairment of water quality and the natural hydrologic function of the river and may be responsible for the decline of dependent species in the watershed. Monitoring activities over the past 20 years have shown that many of the species listed by Schwartzberg and Moore (1995) as historically present are now either locally extinct or critically endangered, including southern steelhead trout, least Bell’s Vireo, and red legged frogs (Court et al. 2000). The continued introduction and impacts of non-native, invasive species pose a significant threat to biodiversity and natural resources in the watershed and have become a key issue in watershed planning and management.
RIVRLab
The RIVRLab has been involved in numerous studies in the Santa Clara system, including evaluation of impacts of Arundo invasion and potential application of biological control of it and other invasive plants such as tamarisk and Cape ivy. In addition, we are evaluating the effects of invasive New Zealand mud snails (Potamopyrgus antipodarum) on native biota, particularly competition with aquatic invertebrates and larvae of the endangered ArroyoToad (Bufo californicus). We are in the process of developing a research station in the watershed to facilitate research on native and non-native species in the watershed, as well as to explore the integration of ecological restoration, biodiversity protection and agricultural sustainability in this valuable floodplain ecosystem.
Arundo Control
One of the proposed control methods for the rapid growth of Arundo Donax has been Teramesa romana, also known as the Arundo Wasp. We detected the Arundo wasp (Tetramesa romana Walker) feeding in Arundo stems in southern California in 2006. This European insect was an accidental introduction in this region, although timing and mode of introduction remain unknown. Currently, the wasp is distributed along the California coast from Santa Barbara County south to Baja California in Mexico, but may continuing to expand its range as we recently (2013) detected new populations in the Mojave River, Victorville, CA. Naturalized populations have also been found in Texas, so this species has most likely been present in North America for several decades. Additional insect populations from Europe were evaluated and augmentatively released in Texas by the USDA. Our Lab continues to track the range expansion and population demographics in Arundo stands in the southwest US and evaluate the direct and indirect effects of wasp herbivory on target plants.