If a species is self-organizing, it can generate non-random spatial patterning among individuals of the species. Observing how non-random spatial patterning of individuals changes over time gives insights into the mechanisms driving pattern formation. Furthermore, non-random spatial patterning in dominant species determines the neighborhood conditions for subordinate species and may have important implications for community assembly. Longleaf pine savannas of the southeastern United States are dominated by tussock-forming grasses and present a rich opportunity to address questions of dominant species interactions. The Nature Conservancy has restored pine savanna groundcover plant communities at Apalachicola Bluffs and Ravines Preserve since 2005, scattering seeds from the locally dominant bunchgrass species, Aristida stricta, over bare soil on different parcels of land each year, forming a chronosequence. Examining the spatial pattern and density of A. stricta tussocks in the chronosequence will reveal how bunchgrass spatial patterns develop and change over time. We established three 2x2 m plots each in areas restored from 2005-2009 as well as in a nearby relict pine savanna site. We mapped the size, shape, and location of each A. stricta tussock >3 cm in diameter onto a gridmap and used Programita to analyze the spatial pattern of tussocks.
Results/Conclusions
A. stricta tussocks occurred in an overdispersed (more regular than expected by chance) pattern in all plots in the chronosequence. The overdispersed pattern was only significant at the plant neighborhood scale. However, the scale of overdispersion increased with time-since-restoration, i.e. A. stricta tussocks were spaced farther apart in plots restored in 2005 than in plots restored in 2009. These results suggest that mechanisms are operating to prevent individual tussocks from growing directly adjacent to one another and that A. stricta tussocks may be self-organizing. Furthermore, the spatial patterns and density of A. stricta tussocks in restored plots closely resembled those of A. stricta tussocks in nearby relict pine savanna sites. This indicates that the restoration methods used were successful in re-establishing A. stricta populations.