Frost‐ring chronologies as dendroclimatic proxies of boreal environments

Frost rings are formed in tree stems when growing‐season frosts affect immature wood cells, producing collapsed cells within annual tree rings. Open boreal forests are most susceptible to record growing‐season frost because they lack the greenhouse effect commonly observed in closed forests. Here we present a novel method to construct regional frost‐ring chronologies in lichen‐black spruce woodlands of the boreal forest zone. Because the ability of trees to form frost rings depends on several factors (including bark thickness and ring width), we used two models to produce a Frost Composite Index based on a frost susceptibility window of cambial age <30 years. The frost‐ring chronology showed alternating periods of high and low frost activity that were highly consistent within and among sites. Reconstruction of growing‐season frost activity may be used as dendroclimatic proxies of climate variability and may give insights into future risks of frost damage in a warming climate.