INTRODUCED AND NATIVE PLANTS OF THE HASTINGS RESERVATION, CENTRAL COASTAL CALIFORNIA - A COMPARISON

Introduced plant species at the Hastings Reservation comprise 17% of t he total flora, and are predominantly annual herbs and grasses. No int roduced species are present in chaparral, coastal sage or rock outcrop s and very few (4% of the total species number) in the mixed evergreen woodland. The highest percentage of introduced species is found in di sturbed areas (40%), such as roadsides and around buildings. Introduce d species have successfully invaded native grasslands (22%), oak footh ill woodland (15%) and riparian areas (15%). In these vegetation types , introduced plants form an integral part, and in grasslands and the u nderstory of oak foothill woodland, annual introduced grasses are the dominant species. The only difference found between established and re corded, but not-established, is that the latter is more recorded in di sturbed areas. This reinforces anecdotal evidence that humans are the main cause of, intentional or accidental, dispersal into this reservat ion and that the most likely habitats of first establishment are the d isturbed areas around houses and roads. Not all introduced species are capable of establishing a foothold in these disturbed areas and an ev en smaller portion is capable of intruding into grassland and oak foot hill woodland. Both these vegetation types are characterized by high n atural disturbance, mainly caused by pocket gophers. Vegetation types with less frequent disturbance, such as chaparral, coastal sage and mi xed evergreen oak woodlands are not, or much less, invasible. Finally, most of the introduced species trace their origin to a similar Medite rranean climate in Europe.