Tree-ring stable isotope relationships to climate across hill-slope positions in boreal Alaska

Background/Question/Methods

Tree ring studies support the idea that summer water stress is an important factor controlling tree growth at many sites in the boreal forest. Prior research using C isotopes suggests that white spruce at warm, low-elevation sites in Alaska were drought-stressed during warm summers. Preliminary tree-ring width data suggest that late season moisture may be a critical component of climate response. Hill-slope position may also play a role in the response of tree ring widths and isotopic composition to climate parameters. In this study we asked the question, does hill-slope position influence the relationship of stable carbon and oxygen isotopic composition of tree rings to climate parameters in Interior Alaska?

Results/Conclusions

Tree ring width indices in white spruce (Picea glauca) are related to climate, with responses dependent on the phase of the Pacific Decadal Oscillation. For example, during warm phases of the PDO, the relationship between growth and temperature was predominantly negative, whereas negative and positive responses to temperature were more evenly split during the cool phase of the PDO. Preliminary results from stable C and O isotope ratios suggest a complex relationship to climate parameters. Surprisingly little variation in ring widths and isotopic composition was found across three hill-slope positions. Further studies will extend the isotopic record back in time, across space to additional hill-slopes and to black spruce (Picea mariana) on varying topographic positions in Interior Alaska.  This study aims to improve understanding of Boreal forest response to climate change and the impacts of this response on vegetation feedbacks to climate change.