Fire is one of the most dangerous factors that lead to significant ecological and economic losses. One of the main components of the substantial loss is the deterioration of the merchantability of pine forests due to deterioration of health of damaged pine stands, depending on the types of heat spread during surface fires. It is important to determine the regional criteria on which the pyrogenic loss of merchantability depends. These criteria will lead to the rational development of forestry activities in burned forests area and minimize the economic losses caused by forest fires.
The aim of the study was to assess the changes in merchantability of the pine stands damaged by surface fires in Ukrainian Polissya zone.
Materials and Methods
Investigation of post-fire changes in health and merchantability of Polissya pine forests was carried out on 20 permanent sample plots during 2012–2016 to diagnose anthropogenic damage of the forest ecosystems. The sample plots were established at five state enterprises of Rivne Regional Department of Forestry and Hunting in accordance with the recommendation of the laboratory of forest ecology of Ukrainian Research Institute of Forestry and Forest Melioration. Characteristics of trees included diameter and height of trees, Kraft class, health condition and the type of fire damage of trees (a char height in stems, an outflow of pine resin on the trunk, the extent of root systems damage).
The dynamics of the pine trees’ health depends on the intensity and the season of fire occurrence, size of trees and its age, the soil type and the duration of the post-fire period. In the years with high rainfall (2012–2014), after surface fires in the “dry” and “fresh” types of soil, damage of the trunk of a tree usually dominated, and in the “moist” and “damp” types of soil, the heat conductivity of the soil was a particular danger, because pine trees develop a surface root system in these conditions. The health of pine forests deteriorated as the post-fire period increased. For forest fires in abnormally “dry” years, the convective type of heat transfer was a common characteristic, and the dominant damage type was not trunk damage but the damage of crowns. In the “moist” type of soil, damage of first order roots prevailed. A month after the forest fire with simultaneous damage to the trunk and crown there was a severe health deterioration and appearance of trees mortality in the damaged stands. In most trees, the color changes of pine needles (deсhromatization) exceeded 70 %, and 30–48 % of trees had a deсhromatization rate of 100 %.
Moreover, even with a slight damage of the trunks (height of char on tree stem was up to 0.5 m), the health condition was evaluated as “dying stands”, and proportion of dead trees was 17 %. In the next 2016, with the exception of the variant with damage to the trunk, a catastrophic deterioration of the condition of pine forests occurred. The most negative changes were observed in “moist” and “damp” types of soil with the root systems type of damage. For pine trees with a dominance of such type of damage, a small proportion of trees with a damaged crown (crown had changed color from green to yellow-brown) were noted. At the same time, the visual effects of root systems damage were detected only one year after the surface fire, when trees mortality reached 100 % even in the stands with minor damage. In the spring of 2016, the pest outbreak was observed (especially Ips sexdentatus, B?rner, 1776) in some pine stands damaged by fire. Their widespread was facilitated by snowless, warm winters. In July 2016, the percentage of dead trees on these sample plots exceeded 90 %.
Ukrainian Polissya is characterized by high merchantability of pine forests. The percentage of merchantable trunks before the fire or in the control plots ranged from 70 to 89 %. The deterioration of pine forests after fires leads to a change in marketability. So almost in all sample plots, which were damaged by fire in years with high precipitation, the yield of merchantable trunks fell from 70–75 to 14–37 %. A particularly significant decrease in merchantability was noticed two years after the fire. At all sample plots, the yield of merchantable wood was in the range of 10–18 %. Particularly catastrophic effects were noted in overmature forest stands.
Although the health condition of pine trees that were damaged by the fire at the end of summer of “abnormally dry” season in 2015 was critical, significant changes in merchantability have not been observed yet in September. The yield of merchantable wood was 77–95 %. A significant decrease (up to 19–40 %) was observed in 2016. At the same time, at three plots, where the char height in tree stem was only 0.31 and 1.06 m, the share of merchantable wood decreased from 83–96 to 0–4 % during this period.
The significant deterioration in merchantability is due to the intensive increasing of stem insects’ population. The inverse correlation between “health condition index” and the yield of merchantable trunks has been established. The direct statistically reliable correlation was established between the intensity of the fire and the decrease in the yield of the merchantable wood during the year after the forest fire. An increase in the intensity of the fire increases the losses of pinewood marketability. The yield of merchantable wood decreases in the damaged stands after surface fires with the increasing fire intensity (the char height on the trunks) and the deterioration in the health of pine stands.
3 Figs., 3 Tables, 13 Refs.