Recent evidence suggests shrub expansion may be a significant contributor to arctic greening. Studies of shrubline are relatively few compared to treeline. Challenges with studying shrubs include their younger age, subtle annual ring structure and atypical plant body. Upsides to studying shrubline may include reduced lag between growth/establishment and climate, the potential for expansion of growth ring studies into treeless areas, and the ability to study treeline dynamics at the community level.

The main focus of the study is aimed at dating birch, Betula glandulosa Michx., along south and north facing transects spanning a Subarctic alpine site in the Mackenzie Mountains, NWT. Shrubs were sampled in August 2007 along the valley bottom to shrubline. Cover and density were also observed. In addition to traditional tree ring sample preparation, techniques involving stains and thin-sections have also been used to improve annual ring resolution. Images of thin sections are currently in the final stages of being prepared. Shrub ages are being used to reconstruct age structures along the alpine transects.

Supplemental to this study is the assessment of the dendrochronological potential of dwarf birch. Samples collected from both Churchill, MB and the Mackenzie Mountains are being used to test whether or not a coherent climate signal or distinct event years are present in the shrub samples. A total of 360 shrubs have been sampled from both sites. In addition to weather station data spanning much of the century, nearby meteorological stations have recorded microclimate data for nearly two decades. Nearby studies of treeline dynamics are also available for comparison to shrubline data. In addition to shrub dates from both regions, detailed descriptions of the methodology and preliminary comparisons of shrub ring-width and climate/tree-ring records are presented.

Acknowledgements: This study was supported by grants from the Northern Scientific Training Program (NSTP) administered through Canadian Circumpolar Institute (CCI) and the Churchill Northern Studies Centre (CNSC) - Northern Research Fund. We thank the staff and volunteers of the CNSC and the Earthwatch volunteers for their contributions to this research, as well as the support and comments of D. Froese and D. Hik during the planning and implementation of this study.