Abstract
Shrub species of southern Californian coastal sage scrub recruit seedlings immediately after fire but also recruit in unburned coastal sage scrub stands and annual grasslands. We examined the influence of natural disturbances other than fire on shrub seedling establishment, especially the role of small-scale disturbance. Our goals were to determine: (1) whether seedling recruitment is associated with gaps in grassland, scrub, and grassland-scrub ecotones; (2) the identity of gap-creating agents; (3) the influences of biotic (vertebrates and ants) and abiotic (late spring moisture) disturbances on seedling establishment; and (4) whether disturbance effects vary spatially, both among and within (gap vs. nongap microsites) the three zones. We censused natural seedlings and vegetation gaps monthly in belt transects for two growing seasons and also measured seed banks at three 16-yr-old sites of adjacent grassland and coastal sage scrub. We initiated factorial experiments at one site to determine effects of animals, gaps, and late spring moisture on seed and seedling numbers. Gap-creating agents varied among the three zones, but seedlings were associated with gaps in each. Animals, especially small mammals, were important in creation and maintenance of gaps. Animal effects varied among but not within zones. Small mammals positively affected seedling recruitment in the grassland (germination on pocket gopher mounds) and negatively affected seed numbers of species with larger and multiple-seeded propagules in the ecotone and scrub; they created and/or maintained gaps in all three zones. Late spring moisture did not play an important role in shrub seedling recruitment in any zone. Because coastal sage shrub seedlings lose transpiring surfaces during drought, they may be less vulnerable than evergreen mediterranean shrubland species to the variability in both annual and seasonal extent of rainfall that is typical of mediterranean climates.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
