Abstract
Abstract 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.
Highlights
Wildfires are one of the most dangerous factors for forests, leading to their destruction and degradation
It has been found that the lethal level of damage to young pine trees is achieved when the relative bark char (Hrel.) reaches 61–70%
We conclude that fire resistance patterns in pine trees change during their growth and vary greatly between different age groups
Summary
Wildfires are one of the most dangerous factors for forests, leading to their destruction and degradation. Many regions of the world have experienced an increasing trend of excessive wildfires and an increasing occurrence of extremely severe fires (FAO 2006). In 2017, wildfires burnt over 1.2 million hectares of natural lands in the EU. The European Forest Fire Information System estimated the amount of fire-related losses to be around 10 billion Euros (San-Miguel-Ayanz et al 2017). In Europe, Scots pine forests exceed 28 million hectares, covering over 20% of the productive forest area (Mason & Alìa 2000). More than 90% of forest fires in Ukraine occur in pine forests (Voron & Melnyk 2009; Voron & Sydorenko 2014). During the last ten years (2009–2018), 19.9 thousand forest fires have occurred in Ukraine on an area of 37.2 hectares. The economic losses amounted to 8.86 million Euros (Public Report 2017)
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