PARENT SESSION
Oral Session # 93: Vegetation Change and Response.
Presiding: B Parry Hecht
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 105.
Patterns of recruitment and mortality in mixed coast live and Engelmann oak woodlands in southern California.
Lawson, Dawn*,1, Zedler, Paul2, Reiley, David2, 1 U.S. Navy, San Diego, California, USA2 University of Wisconsin, Madison, Wisconsin, USA
ABSTRACT- Two species are dominant in lower elevation oak woodlands of extreme southern California -- the widespread Quercus agrifolia (coast live oak) and the much rarer Q. engelmannii (Engelmann oak). Concern about the future of the rarer species is a special case of a more general concern about oak woodlands. In this study we resampled plots in the Engelmann oak phase of southern oak woodland originally sampled ten years earlier. We observed increases in the saplings of both species on a subset of the plots, but the increase was substantially greater for coast live oak. Previous studies have shown that Engelmann oaks were less successful in seedling establishment but had a higher survival into the larger size classes, apparently because of greater ability to survive in gaps. In addition spatial analysis using ARCINFO proximity analysis revealed a significantly greater tendency for live oak saplings to recruit in patches than Engelmann oaks such that live oak saplings are predicted to be less likely to recruit effectively to the canopy. The long term data suggest a more complex pattern of survival and growth in which growth was greater in gaps, but a greater number of saplings were found under the outer canopy of large trees than in either gaps or the inner canopy. These new data suggest that factors allowing the coexistence of these two species may vary over time and are probably more complex than previously believed.
Key words: Quercus engelmannii, mortality, Quercus agrifolia, recruitment