Introduced and native plants of the Hastings Reservation, central coastal California: A comparison

Introduced plant species at the Hastings Reservation comprise 17% of the total flora, and are predominantly annual herbs and grasses. No introduced species are present in chaparral, coastal sage or rock outcrops and very few (4% of the total species number) in the mixed evergreen woodland. The highest percentage of introduced species is found in disturbed areas (40%), such as roadsides and around buildings. Introduced species have successfully invaded native grasslands (22%), oak foothill woodland (15%) and riparian areas (15%). In these vegetation types, introduced plants form an integral part, and in grasslands and the understory of oak foothill woodland, annual introduced grasses are the dominant species. The only difference found between established and recorded, but not-established, is that the latter is more recorded in disturbed areas. This reinforces anecdotal evidence that humans are the main cause of, intentional or accidental, dispersal into this reservation and that the most likely habitats of first establishment are the disturbed areas around houses and roads. Not all introduced species are capable of establishing a foothold in these disturbed areas and an even smaller portion is capable of intruding into grassland and oak foothill woodland. Both these vegetation types are characterized by high natural disturbance, mainly caused by pocket gophers. Vegetation types with less frequent disturbance, such as chaparral, coastal sage and mixed evergreen oak woodlands are not, or much less, invasible. Finally, most of the introduced species trace their origin to a similar Mediterranean climate in Europe.