Key Threats: California/Baja California

Threats to Biodiversity

• Development associated with increased population has reduced many ecosystems to fractions of their former extent. For example, only 10% of riparian habitat in California remains (RHJV 2004).
  
• Coastal ecosystems in Baja California are disproportionately affected by tourism-related developments, which damage ecotourism and traditional livelihoods such as fishing, as well as negatively impact sea turtles, whale sharks, and other threatened and endangered species (Dean & Pesenti 2003; Rodríguez-Estrella 2005).

• Oak woodlands, coniferous forests, and rangelands are increasingly being converted to vineyards (Merenlender 2000). This can cause the fragmentation of mammal habitats as well as impact aquatic systems through chemical runoff (Johnson & Chase 2004).
• Agricultural tilling, high livestock densities, and drought have led to the large-scale conversion of native perennial grasslands to non-native annual grasslands (Barbour & Major 1988; Keeley & Swift 1994).

• Altered fire regimes affect 46% of the mediterranean region of California. Fire suppression has caused fuels to reach unnaturally high levels, resulting in larger, more severe fires (Kilgore 1973, Klinger et al 2006). In addition, fire frequency has increased due to human influences, particularly in coastal scrub and chaparral communities (Davis and Michaelson 1995; Keeley 2001).

• Over 25% of California’s 4,400 plant species are non-native (Rundel 2000), and 73% of these are of Eurasian origin (Arroyo et al 2000). The highest density of invasive flora exists along the coast, where it has a particularly strong impact on coastal dunes and scrub (Randall et al. 1998, Viers et al. 2006, Bossard et al. 2000).
• Coastal forests are being damaged by the Sudden Oak Death pathogen Phytophthora ramorum, which was introduced through the planting of ornamental rhododendron. According to predictive modeling, numerous other areas in California are at risk (Rizzo and Garbelotto 2003; Meentemeyer et al 2004).

• In southern California, air pollution is altering coastal sage scrub systems which is resulting in an increase of invasive annual species and reducing native species richness (Westman 1990).

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