PARENT SESSION
Oral Session #62: Vegetation change: Succession, recovery, facilitation. Presiding: S. Franklin.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Hall of Ideas G.

Competitive and facilitative interactions among two species of coastal dune perennials.

Franks, Steven¹, Peterson, Chris¹, ¹

ABSTRACT- We tested for facilitation and competition within and between two species of coastal dune perennials on Sapelo Island, Georgia and Key Island, Florida. In January 1999, Uniola paniculata and Iva imbricata individuals were transplanted into plots along with four conspecific neighbors, four neighbors of the other species, or no neighbors, at 0, 50, and 100m from the shoreline (N = 2 species x 3 neighbor treatments x 3 locations x 2 sites = 144). The plants were harvested in October 2000. On Sapelo, growth of Uniola targets without neighbors was four times that of Uniola plants with conspecific or heterospecific neighbors (p=0.015), and growth of Iva plants without neighbors on Sapelo was twice that of plants with either species of neighbors (p=0.002), indicating that competition occurred. There was no effect of neighbors on plant growth on Key Island, possibly because severe erosion at this site caused high mortality. There was no difference between interspecific and intraspecific interactions for either target species at both sites. On both Key Island and Sapelo, there was a positive correlation between target survival and the number of neighbors (p<0.0001, Wilcoxon signed rank test), indicating that neighbors may have helped prevent target mortality. It appears that these dune plants may compete for resources but facilitate survival under extreme conditions, which may help to explain their positive associations in the field.

KEY WORDS: competition, facilitation, dune plants, gradients