This thesis examines the long-term threshold response of rainfall-runoff relationships at the Coweeta Hydrologic Laboratory located in the Southern Appalachian Mountains of North Carolina. Threshold relationships between total stormflow and antecedent wetness represent an important emergent behavior that has been observed in previous studies. These studies are limited to only several years of analysis, which raises questions about longer term non-stationarity in threshold response. To examine the influence of non-stationarity, this thesis uses 15 years of data collected by the Coweeta Long-Term Ecologic Research Study and USDA Forest Service at two long-term monitoring sites to supplement additional short-term observations. Results demonstrate that threshold behavior of stormflow generation exists in Coweeta as a function of total storm precipitation plus antecedent soil moisture. Long-term thresholds vary with respect to seasonality and interannual hydroclimate variability. Lastly, we found evidence of non-linear stormflow generation, which has implications for previously observed simple threshold behavior.