Abstract
Recent shifts in the hydrologic regime of the Apalachicola River have been attributed to anthropogenic changes in the watershed, particularly those associated with dam and reservoir construction. To assess the impact of these changes on the forests on the river’s floodplain, a two-tiered methodology was applied to a 1-ha forest plot. First, repeat-survey data spanning a 27-year interval was subjected to multivariate analysis for identification of major trends in forest composition. While the changes identified were small, the increased representation of upland tree species on the plot was a potential indication of ecological response to declining river stages. To examine patterns in tree growth in more detail, a dendrochronological approach was used, beginning with the collection of core samples from every species present on the plot. Of these, cores from 4 different species were selected as suitable for analysis. The annual growth increment record from these cores was subjected to correlation and multiple regression analysis with various hydrologic and climatic parameters in an attempt to isolate the primary factors influencing growth. The use of the hydrologic analysis software IHA allowed the development of parameters characterizing the site-specific flooding regime, including parameters approximating annual frequency, average duration, and average timing of inundation events. Finally, intervention detection analysis was used to identify major trends, shifts, and unusual features in the growth record. Growth in all four species was found to correlate most strongly with hydrologic parameters, particularly with the site-specific parameters generated by IHA. Regression models developed primarily from hydrologic parameters were successful in accounting for variance in growth in all four species, particularly after removal of disturbance-related outlier years (0.36 < adjusted r2 < 0.52). The trend toward lower stages caused by dam-induced channel degradation has been one among many factors, several of them potentially anthropogenic, influencing patterns in tree growth over the past half-century.
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