Date of Award
Doctor of Philosophy (PhD)
William J. Platt
Many biotic and abiotic factors contribute to the formation of aggregations of seedlings and juveniles in populations of forest trees. The following studies investigate factors influencing the spatial structure of juveniles in an old-growth longleaf pine (Pinus palustris Mill.) population. In the first study, effects of adult tree density, pine needle litter and fire temperature were related to the demography of juveniles. A cohort of juveniles from a mast year in 1987 was followed over four years. Demographic components were determined both before and up to two years after fire. Juveniles were more dense, larger and had higher survival in areas of low adult density where needle litter and fire temperatures were lower. Effects of adult trees on juvenile size and survival prior to fire was considered in the second study. The impact of nearby adult neighbors was estimated as the cumulative size and number of all neighboring trees within concentric zones located from juvenile plots. The results demonstrated that larger sized adults had greater effects on juvenile size and survival. The third study investigated the importance of seed dispersal patterns on the spatial structure of longleaf pine. This was the first study of its kind to use multilocus allozyme markers to differentiate overlapping seed shadows within a natural forest stand. Maternal parents of seeds were determined using maternity exclusion analysis. A dispersal range for longleaf pine was described. In addition, potential dispersal distances were estimated from differences in seed morphology, terminal velocities, and rate of descent. Evidence from both the allozyme and morphological data indicate that longleaf pine seeds have the potential to disperse long distances from maternal parents. The dispersal range predicted exceeds previous reports of dispersal for longleaf pine. This may be attributed to differences in physical structure of the old-growth stand utilized in this study compared to second growth stands used in previous studies. The potential for long distance dispersal in longleaf pine can result in propagules being widely dispersed within local populations. This, in turn, could have a strong impact on the spatial and genetic structure of longleaf pine stands.
Grace, Susan Langevin, "Demographic and Genetic Studies of Seed Dispersal and Juvenile Survival in an Old-Growth Longleaf Pine Population." (1994). LSU Historical Dissertations and Theses. 5798.