PARENT SESSION
Oral Session #56: Spatial Ecology: Pattern,movement,dispersal.
Presiding: G. Hartvigsen
Wednesday, August 7. 8:00 AM to 11:30 AM. Grand Ballroom West, Radisson.

Local-scale pattern in a California sage scrub community type: The importance of local interactions.

Chalekian, John^*,1, Deutschamn, Douglas¹, ¹ San Siego State University, San Diego, Ca

ABSTRACT- Quantifying spatial patterns in plant communities provides insight into the fundamental processes responsible for pattern formation and improves our ability to make inferences. Spatial patterning may reflect large-scale gradients (e.g. elevation) as well as fine-interactions (e.g. dispersal, local competition) in the system. Therefore, separating exogenous pattern from endogenous pattern is challenging due to this mixing of spatial scales. Local patterning of vegetation in a disturbed California Sage Scrub community was quantified using Spatial Auto-Correlation (SAC) analysis. Density of native shrubs and invasive annuals were mapped and analyzed in three 25x25-meter plots in Southern California. Initial spatial analyses indicated the presence a broad-scale gradient. Removal of the broad-scale pattern, via Trend Surface analysis, allowed us to identify strong repeatable local-scale patterning. Native plants and invasive annuals were spatially aggregated at a scale of less than 10 meters, consistently across the landscape. Spatial Cross-Correlation analysis indicated the two guilds were aggregating antagonistically at this scale. The scale of this local patterning was found to coincide with the scale of spatially limited biological processes, notably seed dispersal and competition. These results suggest patterning in vegetation is a consequence of local biotic interaction.

KEY WORDS: Spatial auto-correlation, Spatial cross-correlation, trend surface analysis, local interactions