Restoring Conservation Nodes to Enhance Biodiversity and Ecosystem Function along the Santa Clara River

The Santa Clara River watershed in Ventura County features southern California’s last non-channelized and least ecologically disturbed major river system (Figure 1). The watershed encompasses an area of great biological richness and lies within a globally significant biodiversity hotspot (Myers et al. 2000) along the California South Coast. The resources and habitats within the Santa Clara River watershed are increasingly threatened by an array of problems related to human population growth, land-use conversion, and modifications to the river’s natural hydrology. To address these threats, The Nature Conservancy (the Conservancy) has been working for the past 15 years to protect intact habitat within the watershed, and enhance riparian biodiversity through restoration projects.

The concept of protecting large landscapes to maintain biodiversity has been one of the key applications of island biogeography theory (MacArthur and Wilson 1967) to conservation practice. Larger wetland restoration projects have been shown to have faster rates of biological, hydrological, and biochemical recovery, and to be more self-sustaining over time (Moreno-Mateos et al. 2012). The Conservancy is applying these principals to the conservation on the Santa Clara River by hypothesizing that the riparian corridor and floodplain would best support native habitat through the protection of larger contiguous sections of riparian habitat, as opposed to several smaller individual parcels dotted along the river’s main stem.

Within the field of restoration ecology, this approach has been referred to as the “string-of-pearls” approach, where protected sites along riparian corridors or terrestrial habitat that is surrounded by urban areas or agricultural lands are ecologically restored to produce an integrated system of discrete habitat blocks, much like a string of pearls. These habitat blocks should be close enough together to facilitate wildlife movement and support ecosystem processes. Through land acquisition, the Conservancy has managed to protect a string of habitat blocks along the Santa Clara River. Here we provide an overview of the Conservancy’s strategic land protection efforts, and describe the multiple benefits to be derived from the shift that the organization is currently making in this geography—from solely acquiring lands, to planning and implementing restoration.

Figure 1.

The Santa Clara River in Ventura County, CA, USA. Photo credit: Melinda Kelley for The Nature Conservancy.

In 1992, the Conservancy completed a bioregional conservation analysis for the South Coast Ecoregion of California (TNC 1993) to identify large areas with generally intact natural habitats that support the biodiversity of the ecoregion. Due to the scarcity of wetland habitats in Southern California (Zedler 1996), and the fact that 38 special status species are found within the Santa Clara River watershed, the river and its tributaries were identified as a conservation priority for the Conservancy. Additional assessments of the Santa Clara River conducted in 1999 and 2001 identified four priority areas or “conservation nodes” where conservation efforts would be focused (Figure 2). These plans were further refined with completion of upper and lower river Conservation Action Plans (TNC 2006, 2008), and an additional conservation node was added in 2012 to ensure protection of a rare habitat type in an area of the river that is intermittently dry. Unlike many other rivers, the riverbed of the Santa Clara is almost entirely privately owned. Therefore, the Conservancy’s initial decade of work focused on protecting the priority conservation nodes by acquiring land from willing sellers. Despite strong county growth controls, prime farmland in Ventura County can exceed $80,000 per acre, and developable land can be worth several times that amount. Only land with little or no economic value can be acquired in large blocks needed to achieve effective conservation. For example, land within the floodway of the river is highly regulated by state environmental agencies and is impractical to develop because of the risk of destructive flooding. Therefore, private lands in the floodplain are of little or no use to their owners, and the Conservancy is typically able to acquire these parcels of riparian habitat at $750 per acre.