DO SHRUB COLONIZERS OF SOUTHERN CALIFORNIAN GRASSLAND FIT GENERALITIES FOR OTHER WOODY COLONIZERS?

Grasslands are subject to woody plant invasions worldwide. To retain landscape mosaics of woody and grassland vegetation, preserve managers need to understand how vegetation boundaries shift. Woody plant colonization of grasslands without fire is widely known in mediterranean‐climate regions, yet few generalities have emerged for woody colonizer traits or colonization processes. Here we report on our research into processes of grassland colonization by summer deciduous coastal sage scrub species of semiarid southern California. We used four coastal sage shrub dominants to elucidate dynamics of grassland colonization and within‐stand replacement. We measured seed production, dispersal, and storage; seedling numbers; and growth and flowering for two years in three grassland‐scrub sites. Traits of our four species matched those of native woody colonizers as described in other systems and included: recruitment over a range of site conditions, annual production of large seed crops, long‐distance dispersal (into grassland), presence in grassland seed banks, seedling recruitment in gaps, rapid seedling growth, and low susceptibility to seedling herbivory. In a factorial experiment, we used our study species to test a set of hypotheses that explain grassland colonization by a northern Californian shrub species and found overall greater importance of biotic disturbances but less influence of water availability. Although generalities can be made about some native woody colonizer traits, to maintain mediterranean grassland–shrubland mosaics we encourage land managers to devise monitoring and management plans that sufficiently address local shrub species traits and environmental factors.