Geographic and Ecological Variation in Seedling Growth Rates of Sand Pine (Pinus clausa)

We harvested seedlings from across the range of sand pine (Pinus clausa) in order to estimate seedling growth rates. We found significant differences in seedling growth rates between its two varieties. Ocala sand pine (P. c. var. clausa) on the Florida peninsula commonly regenerates following crown fires on open ground, seedling growth was rapid on these sites Choctawhatchee sand pine (P. c. var. immuginata) on the Florida panhandle commonly regenerates in the sand pine forest understory, often in canopy gaps formed by wind damage. Seedling growth was slower and more variable in these settings. Heat and water stress at a modern dune site on the panhandle yielded the slowest seedling growth. At Eglin Air Force Base, fire suppression has allowed sand pine to invade longleaf pine savannas. Seedling growth rates across a gradient of invasion revealed no significant differences between sites from the historical core of sand pine's range in coastal lowlands and older invasive sites, where dense sand pine cover has developed. By contrast, recently invaded sites showed rapid seedling growth, not significantly different from values obtained for Ocala sand pine seedlings following crown fires.