Forest Dynamics on the Hickory Ridge of St. Catherines IslandAlastair Keith-LucasForestry and Geology Department, University of the SouthIntroductionSite Inventory ResultsMethodsDiscussions and ConclusionsAcknowledgementsI would like to thank Nicole Nunley for her assistance in map making and GPS programming and Ken Smith and Royce Hayes for their guidance and resources throughout.This study took place at the Hickory Ridge on St. Catherines Island, Georgia to assess the state of the tree population after the widespread parasitic destruction of the local red bay. A previous study on this site indicated that the pignut hickory population was in a period of decline (Eric Keen, 2008).
My specific objectives were to:Map, inventory, and measure individualstems and overall ground coverage at 9 separate plots.(2) Create a photographic record from plot centers.(3) Identify and prepare exclosure areas for Pignut hickory regeneration.Field Methods Plot centers marked via GPS Stems of height 1.30 m or greater recorded for DBH, species, bearing and distance from plot center. Palmetto coverage recorded and mapped within plot.Ground cover recorded. 2 m radius wire exclosures constructed along periphery of plots in open canopy areas near potential seed treesPhotographs taken from plot centers toward cardinal directions.Laboratory MethodsPlots drafted by hand into maps.Paper maps converted with GIS software into digital maps Stem Regeneration: The widespread evidence of deer habitation and browse coupled with the almost complete lack and eventual disappearance of hickory seedlings suggests that herbaceous predation is a factor in the poor recruitment of the pignut hickory
State of the redbays: Redbays on the hickory ridge suffered an observed 97% mortality rate during the blight, which began in 2004. Redbays composed as much as 20-25% of all stems across the area, leaving gaps in the canopy where other species, the pignut hickory in particular, would typically take root.
Hickory Presence: While the pignut hickory is widespread and shows great variance in age and size, no observed seedling survived to the end of the survey and no living stem was small enough to be of an age less than several decades old, meaning that there is no evidence of reseeding in the wake of the disappearance of the redbay despite opportunity of growing space, observably positive growing conditions, and the adjacency to productive seed trees.
Looking Forward: An exclosure has been constructed near to each plot edge. They have been built under open canopy close to mature, productive hickories that will likely act as seed trees. These structures will prevent herbaceous predation for the foreseeable future, protecting seedlings as they grow. These exclosures could potentially facilitate the growth of hickory in the area and add a much needed younger generation of trees.
Inventory: 295 mature trees were found across 9 plots, 232 of which were living trees, 63 of which were dead.Living Species Composition: Pignut Hickory is currently the dominant species among living stems in the area, the majority of stems per hectare and the highest average DBH of all species. Red Bays composed less than 1% of the live stem population, with only 1 remaining live tree across all plots. Of secondary presence were American holly and SparkleberryDead Species Composition: Of 63 standing dead trees, 43 were redbay, 19 were pignut hickory. Many of the remainder were impossible to identify due to rot.Ground Cover: Palmetto coverage varied from 0% coverage in plot 7 to 60% in plots 5, 3, and 6. No hickory seedlings were found in palmetto, contrary to prediction.Basal Area: Hickory live basal area averaged 13.2 m2 per hectare, while non-Hickory averaged 3.4 m2. Pignut Hickory composes 79.5% of live basal area across all plots.
Site Description9 circular plots of 17.38 m radius (1/10 hectare) size in 3 transects of 3 plots each. (Figure 1)
Figure 1, Infrared map of Hickory Ridge with all 9 plots. Note that plots are arranged roughly into transects of 3 plots each, and they are located in three areas outside of the islands old cotton fields.
Figure 2: A photograph of Plot 7 pointing due south from plot center. Note the high cover of the warm season grass (Chasmanthium).Figure 3: Plot 7 digital map with trees symbolized by diameter, species, condition, and location in the plot. Note that there was no palmetto at this plot, rare for the study site. All plots were mapped in this way.Figure 4: Distribution of hickory vs, non-hickory trees by diameter class across all plots. In the larger diameter classes, Pignut Hickory generally outnumbered non-hickories.Figure 5: Live species distribution at each plot. Species distribution varied from plot to plot considerably, yet pignut hickory was invariably the dominant species, and was often followed distantly by American Holly and Sparkleberry. Figure 6: Hickory basal area vs non-hickory basal area at all plots. Note the overall dominance of hickory stems at every plot.1