Postfire tree mortality and fire resistance patterns in pine forests of Ukraine

The study was conducted in pure Scots pine (Pinus sylvestris L.) stands within the forest steppe physiographic region of Ukraine damaged by surface fires with different intensity. The aim of the research is to determine the effect of different fire intensity on pine stand and individual trees, considering tree morphometric parameters and type of damage. The intensity and duration of fire-related tree mortality was different in stands with different age. We found that tree fire resistance is driven by tree diameter, height of the rough bark, and natural degree of thickness. The proportion of dead trees one year after the spring fires in the middle-aged pine stands was 5 times lower and in mature pine stands even 10 times lower than after the summer fires. The critical damage to tree crowns in young pine trees causing their death is 80% of the needles burned. In the middle-aged pine trees, critical damage depended on the size of trees. The death of large, mature trees after smoldering summer fires was associated with the accumulation of a large stock of forest litter and duff near the tree-base, which contributed to the increased intensity of fire and its localization near the base part of the trees. Based on our findings, postfire tree mortality models have been developed for different age groups of pine stands.