PARENT SESSION
Poster Session #53: Plant Competition.
Thursday, August 8. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Spatial association between two woody plants in a savanna system:evidence for facilitation?

Batchelor, Margaret^*,1, Fowler, Norma¹, McNally, Michelle¹, ¹ University of Texas, Austin, TX

ABSTRACT- Facilitation (the positive effects of one species on another), in theory, could lead to positive spatial associations between species. Competition (the negative effects of one species on another) could lead to negative spatial associations. The magnitude and the direction of the spatial association between Quercus fusiformis (hereafter Quercus) and Juniperus ashei (hereafter Juniperus) were measured in multiple savanna sites on the Edwards Plateau in central Texas. Stratified random sampling was used to determine the number of Juniperus individuals in each of three size classes found in each of three types of habitat (under Quercus canopy, under Juniperus canopy, and in open grassland). This observed spatial distribution was compared with the distribution generated by a null model that assumed no interaction between Juniperus and Quercus. Juniperus individuals were found in higher than expected frequencies under the canopy of Quercus and in lower than expected frequencies in the open grassland. The positive association with woody canopy was significant for all size classes of Juniperus, but the strength of the pattern decreased with size. Mechanisms other than facilitation could explain the spatial distribution of Juniperus on the Edwards Plateau (e.g. seed dispersal). This study suggests, however, that if facilitation exists in this system, it probably occurs between Quercus and Juniperus during the early stages of the life history of Juniperus. Field experiments are presently in progress to test these and related hypotheses.

KEY WORDS: facilitation, spatial association, Juniperus ashei, species interactions