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1 January 2011 Rock Outcrops Harbor Native Perennials in Type-Converted Coastal Scrub
Robert J. Steers
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Type-conversion of coastal scrub to exotic annual grassland has been extensive in certain parts of southern California, especially in drier inland locales. Field observations suggest that rock outcrops harbor native perennials associated with coastal scrub vegetation after conversion to exotic annual grassland has occurred. Surveys were conducted to test this observation. In addition, measures of fossorial mammal disturbance, soil depth, exotic annual plant abundance, and soil moisture were collected and used to infer potential mechanisms that may influence patterns of native and exotic vegetation. Results showed that larger outcrops are associated with more native perennial species than smaller outcrops, consistent with predictions based on species-area relationships. In addition, the edges of rock outcrops were shown to have greater native perennial species richness than the surrounding exotic annual grassland matrix. Higher soil moisture, lower soil depth, and less disturbance by Botta's pocket gopher (Thomomys bottae) were also found at the edge of rock outcrops compared to the surrounding grassland matrix. Furthermore, soil depth was positively correlated with pocket gopher disturbance and with exotic annual grass cover. Rock outcrops serve as refuge habitat for native coastal scrub perennials in areas where exotic annual grasses have become dominant. Rock outcrops may become increasingly important for conservation efforts if remaining coastal scrub vegetation continues to deteriorate.

© 2010
Robert J. Steers "Rock Outcrops Harbor Native Perennials in Type-Converted Coastal Scrub," Western North American Naturalist 70(4), 516-525, (1 January 2011).
Received: 6 July 2009; Accepted: 1 July 2010; Published: 1 January 2011
alternate stable states
coastal sage scrub
fossorial mammal disturbance
habitat heterogeneity
invasive species
plant-animal interaction
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