TWENTY-THREE. Grasslands

Abstract

Much of California’s original grassland habitat has been lost to both changes in hydrology and in urban and agricultural development. Even with this extensive habitat loss, more than 10% of California’s land area remains covered by grasslands today (Corbin et al. 2007a, Barbour et al. 2007). These remaining grasslands are among California’s most altered ecosystems (Corbin et al. 2007a, Janzen et al. 2007). Nonnative plant species comprise more than 90% of plant cover in most grassland areas, with many sites below 1% native cover (Bartolome et al. 2007). Even in their non-native dominated state, California’s grasslands are a tremendous diversity hotspot, averaging more than fifty plant species per 30 x 30 meter area (Heady et al. 1991) and providing habitat for nearly 90% of state-listed rare and endangered species (Skinner and Pavlik 1994) and seventy-five federally listed plants and animals (Jantz et al. 2007). These grasslands provide many ecosystem services critical for adjacent agricultural and suburban/urban areas. Almost all of California’s surface water passes through grasslands and oak woodlands (Tate et al. 1999). The grasslands provide high infiltration rates that attenuate storm events, leading to gradual release of storm water to streams (Lewis 1968, Dahlgren et al. 2001). This reduces flood risk while also maintaining streamflow into the dry season. Grasslands can also improve water quality by filtering pathogens, nutrients, and sediments, serving as effective buffer strips between agricultural and urban uplands and streams (Tate et al. 2006, Atwill et al. 2006). California’s grasslands contribute significantly to regional carbon storage through their large spatial extent and high quantity of carbon storage per unit area (Silver et al. 2010). Grasslands also support many of the pollinators needed in California’s crop systems (Chaplin-Kramer et al. 2011). Direct economic benefits of these grasslands include their provisioning of 75% of the state’s livestock forage (Corbin et al. 2007a, CCCC 2009, Cheatum et al. 2011). Because 88% of California grasslands are privately owned (Jantz et al. 2007), their conservation and restoration depend largely on private land owners and the ways they balance management for livestock production, biotic diversity, and ecosystem services (SRDC 2006, Barry et al. 2006, FRAP 2010, Ferranto et al. 2011). Managing California’s grasslands can be challenging because their structure and function are influenced by multiple, interacting controllers. This produces heterogeneous AQ: no Janzen in refs— do you mean Jantz et al. 2007?