A Case Study: Growth of Tree-Form Willow Driven by Cool, Wet Springs and Warm, Dry Summers in Teetł'it Zheh (Fort Mcpherson), Northwest Territories, Canada

Willow trees (Salix alaxensis) growing along the Peel River floodplains near Teetł'it Zheh (Fort McPherson), Northwest Territories, Canada, have been identified as a species of interest because of their impressive height and novel growth form. These willow stands are characterized by tree-form individuals covering 2000–3000 ha. Little research has been directed at understanding the climate–growth relationships of willow in this growth form or region. In this case study, we evaluate the dendrochronological potential of these willows, and assess climate–growth relationships for monthly temperature, precipitation, and SPEI (Standardised Precipitation Evapotranspiration Index) variables. We found that individual trees exhibited a common stand-level pattern of growth variability. Climate–growth correlation analyses indicate willow growth is positively related to May SPEI (r = 0.392) and the mean of June and July maximum temperature (r = 0.341). Willow growth exhibited a negative relationship with May maximum temperature (r = -0.458) and mean June/July SPEI (r = -0.338). These findings suggest there is a general climate response, where willow growth is greater in years with cool, wet springs, and warm, dry summers. Our results provide the first documentation of climate–growth relationships for willow in tree growth form and provide promising preliminary uses of tree-form Salix spp. for dendrochronological analyses.