Masters Theses

Date of Award

5-2004

Degree Type

Thesis

Degree Name

Master of Science

Major

Geography

Major Professor

Henri D. Grissino-Mayer

Committee Members

Sally P. Horn, Kenneth H. Orvis

Abstract

Torreya taxifolia has thrived in the bluffs and moist hammocks along the Apalachicola River in northern Florida and southern Georgia for thousands of years. This species underwent a drastic decline in the mid-1950s. A stem and needle blight, similar to that which destroyed the American chestnut, has resulted in widespread mortality and a virtual halt in sexual reproduction in Torreya throughout its natural range. Because no single invasive, lethal pathogen has been isolated, possible environmental factors that would cause decreased growth and resistance to disease are being examined. Among these factors are changes in local climate and land use regimes. A study of the climate history within the habitat of T. taxifolia may identify the change(s) that have initiated and are currently causing the decline of this species. In addition a climate/growth model for this species should benefit restoration and reintroduction programs.

Increment cores and cross sections were taken throughout the range of T. taxifolia. Because T. taxifolia is an endangered species, no samples were taken from live trees. Cross sections were cut from remnant logs of Torreya, and increment cores were extracted from nearby pines. A total of 29 Torreya cross sections and 150 pine increment cores were taken from the collection sites at Woodruff Dam, Torreya State Park, and the Apalachicola Bluffs and Ravines Preserve (ARBP). The samples were prepared and measures using standard dendrochronological techniques. Correlation analyses were conducted using local climate data, including precipitation, temperature, and drought (PHDI) for the purpose of modeling tree-growth response to local climate. Early period and late period growth patterns were compared to determine if a certain mechanism in the local environment weakened these trees making them more susceptible to the stem and needle blight. Historical accounts of change in the habitat and surrounding area were also reviewed to determine if anthropogenic habitat changes, such as the construction of Woodruff Dam near Chattahoochee or local clear-cutting operations, contributed to the increase in mortality of T. taxifolia.

A master chronology extending back to 1896 was established using 125 pine cores. Twenty of the T. taxifolia cross sections were successfully dated, extending the chronology back to 1814. I found a significant positive relationship between growth and spring precipitation and an inverse relationship between growth and summer drought severity and summer temperature. The climate-growth response of T. taxifolia mirrored that of the pines, but was not as intense, possibly because of the protected understory habitat.

The correlation between tree growth and precipitation suggests that moisture is the strongest determining factor of growth in this area. The inverse relationship with temperature illustrates the effect of higher temperatures on available moisture. A drought and warm period occurred simultaneously during the mid-1950s in combination with heightened clear-cutting practices and the construction of Woodruff Dam. It is my conclusion that habitat deconstruction occurring as early as the turn of the 20th century began weakening the Torreya. The unfavorable climate conditions and rapid degradation of the habitat occurred during the mid-1950s further weakened the Torreya and allowed them to succumb to terminal infection by the blight.

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