DENDROCLIMATIC ANALYSIS OF CLIMATE OSCILLATIONS FOR THE SOUTHEASTERN UNITED STATES FROM TREE-RING NETWORK DATA

Dendroclimatological research along a geographical gradient is important to understanding both spatial and temporal characteristics of climate influences on tree growth. In this study, three tree-ring width chronologies, obtained from field collection and previous research, were used to represent tree growth along a longitudinal transect from coast to inland in the southeastern U.S.: Hope Mills, located at the Atlantic Coastal Plain; Linville Mountain, located on the eastern side of the Appalachian Mountains; and Gold Mine Trail, located on the western side of the Appalachians. The variations of ring width indices in chronologies reflect extreme climatic events such as severe droughts or cold periods. Correlation and response function analyses were used to examine the climate-tree growth relationship at three sites. The temporal stationarity of climate signals was tested using moving interval analysis in DENDROCLIM2002.

Winter temperature was the limiting climate factor for the western mountain site, while moisture was more important for tree growth in the eastern mountain and coastal area sites. However, all significant climate signals found in the trees were not stable over time. The tendency of a shift from precipitation signal to temperature signal is notable around the mid-20^th century. Winter North Atlantic Oscillation (NAO) had positive correlations with radial growth at the two mountain sites, which might explain the winter temperature response by trees. The Atlantic Multidecadal Oscillation (AMO) showed an annual feature of associations with growth, and the multidecadal duration of significant correlations was also apparent. The Pacific-related Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO) also tended to influence tree growth. Along the coastal-inland transect, gradient features of climate oscillation signals did exist. Relationships changed with phase changes of the oscillations. Land-sea boundaries and high mountains may determine the climate response patterns in the Southeast. Other factors such as microenvironment, human disturbance, and biological reaction of trees to climate change also have influence. It is not reliable to use the composite chronology to study the effect of climate oscillations for the Southeast region. In the future, a large number of sample sites will be necessary to more extensively study the regional climate-tree growth relationship.