Growth responses of Pinus elliottii to Hurricane Katrina (2005) on Cat Island, MS - The role of elevation

Background/Question/Methods

The Mississippi – Alabama Barrier islands serve to buffer their corresponding coastal areas from impacts of hurricanes and other extreme weather. On August 29, 2005, they were impacted heavily by the wind, waves, and storm surges of Hurricane Katrina. The spatial variability of growth response (GR) and stem diameter (SD) was examined in Pinus elliottii Var. elliottii, a dominant tree species on Cat Island, Mississippi, in relation to the impact of Hurricane Katrina. The main objective of this study was to determine GR of P. elliottii to Hurricane Katrina, measure SD, and examine their relationship to elevation. The hypotheses tested were: 1) Growth rates of P. elliottii were decreased by the impact of Hurricane Katrina 2) The largest trees occur at the highest elevations. Remotely sensed data was used in conjunction with ground data. Tree cores were extracted from selected trees using a proportional systematically aligned spatial sampling method: The point – centered quarter distance method. At each sample site, two – four radii were extracted from each tree, as well as SD, GPS location, and elevation recorded.  

Results/Conclusions

Tree cores divulged historic, undocumented, land-use information through their “turpentine” growth signatures. Current results indicate stand establishment as far back as 1896. GR was tested within a seven year window pre and post storm and expressed as millimeters of radial growth per year. A difference of means test proved there was a significant difference in growth between the two time periods. A one-way analysis of variance (ANOVA) between four equal blocks of elevation show a relationship between average SD and average elevation. Growth retardation to Hurricane Katrina and other major historic hurricanes was most prominent in trees at lower elevations. For example: Trees located at corresponding lower elevations of the dune-swale systems had similar GR to Hurricane Gustav (1998) and Katrina (2005) on the magnitude of four years. Some trees at the lowest elevations appeared to be still recovering. The results of the statistical analyses confirm both hypotheses. However, a small percentage of trees at the highest elevations, located in the central, more protected part of the island, show no retardation in growth at all. This was attributed to a number of factors such topography, distance to shoreline, stratigraphy, infiltration, recharge, and micro-differences in elevation.