Windthrow mortality influenced by natural root grafting in boreal jack pine forests

Natural root grafting reduces tree uprooting likelihood and promotes stem breakage during windthrow events. Windthrow is a natural disturbance affecting forest dynamics, characterized by tree uprooting or stem breakage when wind forces surpass tree anchorage strength or stem resistance. Windthrow mortality has been related to several ecological biotic and abiotic factors. However, the influence of natural root grafting on windthrow mortality remains unknown. This research evaluated the influence of root grafting on windthrow mortality by excavating root systems of jack pine (Pinus banksiana) in four windthrow-affected riparian buffers and analyzing root grafts using a dendrochronological approach. Our results revealed that natural root grafting decreased the uprooting likelihood but increased the propensity for stem breakage. In addition, root grafting occurred more frequently in trees closer to one another. These results suggest that root grafting influences the windthrow mortality type, with tree proximity being a good predictor for root grafting. This study provides valuable insights into windthrow dynamics, particularly relevant for managing windthrow mortality following partial harvesting and riparian buffers, conserving soil, and mitigating the impacts of windthrow events in the face of climate change.