Influence of climate and disturbance on the growth of Tsuga canadensis at its southern limit in eastern North America

It has long been hypothesized that trees growing at range limits likely also occur near the limit of their ecological amplitude and thus, should be more sensitive to climate variability than individuals growing nearer the range core. We developed a tree-ring chronology using Tsuga canadensis individuals from three disjunct stands at the species’ southern limit to quantify the influence of climate and disturbance on radial growth patterns. The tree-ring record extended 158 years from 1850 to 2007. Significant negative relationships were found between the STANDARD chronology and monthly mean temperature, monthly maximum temperature, and monthly minimum temperature during the previous and current summer, while significant positive relationships were documented between the STANDARD chronology and monthly minimum temperature for September and October of the current year. Also, significant positive relationships were documented between the STANDARD chronology and monthly total precipitation for September of the previous year and May of the current year. Response function analysis showed that monthly climate variables (r ² = 0.22) and prior growth (r ² = 0.40) explained 62% of the variance in the T. canadensis tree-ring chronology. A time series plot for the T. canadensis chronology showed that actual tree growth agreed relatively well with the predicted growth based on significant climate variables. However, positive departures from the predicted growth were noted. Dendroecological analysis revealed these departures were likely related to disturbance events. Our results indicated that T. canadensis individuals at its southernmost extent are sensitive to regional climate, but not more so than trees nearer the range core. We hypothesize that microenvironmental conditions of T. canadensis stands at its southern limit are similar to conditions within the contiguous distribution of the species, which may explain this pattern.