Frost crack incidence in northern hardwood forests of the southern boreal-north temperate transition zone

Frost cracks are common in northern hardwood stands near their northern range limits. Although they have long been attributed to the regional climate, temperature fluctuations result in surface cracks largely when internal wounds are present. We examined the relationship between the proportion of trees with frost cracks and both tree-level diameter class and stand structural characteristics in primary stands with a history of minimal logging (n = 4) and 67- to 97-year-old second-growth stands subjected to past heavy partial cuts and high grading (n = 8). We hypothesized that frost crack incidence would (1) be greater in the second-growth stands and (2) be associated with differences in structural attributes between the two stand types. High levels of frost cracking in primary stands indicated that cracks are not completely avoidable. However, the proportion of trees with frost cracks was significantly higher in second-growth than primary stands, particularly on small-diameter trees. For example, the odds for frost cracking were 1.66-3.74 times greater in second-growth than in primary stands in the 15-cm diameter class, but were not different in the 45+-cm diameter class. Frost cracking was positively associated with increasing diameter in both stand types. Structural characteristics reflecting tree size, stand basal area, and basal area of hardwoods were positively associated with the proportion of trees with frost cracks in second-growth stands but not in primary stands. Although the basal area of conifers was negatively associated with frost cracking, the effect was likely due to a reduction in hardwood basal area in the vicinity of conifers. We suggest that greater frost crack incidence in second-growth stands is likely a consequence of injuries to residual trees during selective logging.