Stable isotope dendrochemistry of needles, twigs, and tree rings were used to identify the impacts of a changing global atmosphere in two separate environments with different anthropogenic loads: the boreal forest surrounding the Athabasca Oil Sands region (AOSR), Alberta, Canada, subject to a large point source of anthropogenic emissions, and the relatively isolated alpine environment of Grand Teton National Park (GTNP), Wyoming, USA. In the AOSR, neither δ13C, δ15N, or the C/N ratio in needles and twigs identified the spatial extent of emissions, but tree ring chronologies did highlight shifts in the nitrogen cycle due to increased anthropogenic nitrogen deposition since the beginning of economic development. Alternately, stable isotope geochemistry of tree ring chronologies in the GTNP indicated a greater impact on ecosystem dynamics from increased levels of CO2 and climate change, reflecting water constraints and increased intrinsic water-use efficiency in trees. The ability of stable isotope dendrochemistry to record both nutrient cycle dynamics and physiological responses to the atmosphere makes it a valuable tool in monitoring the long-term effects of increasing anthropogenic emissions which will result in more pronounced impacts in the future.