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Abstract
Introduction
Large wildfires are hugely destructive for the forests. This is severe issue for many countries around the world. Extensive forest fires which involved a risk of a natural disaster negatively affect the environment, change the natural processes in some forest ecosystems and lead to significant environmental, economic and social losses. The information on the stocks of forest fuels will enable assessing and more precisely predicting the main characteristics of possible forest fires and their possible consequences, which in turn will contribute to more effective fire management. This information is also needed to determine the level of fire risk in the research area. Information about the forest fuel distribution in the area, including information on the history of forest fires, will allow the further mapping of forest fuels and the development of activities for the protection of forests from fires.
The aim of the study was to determine the forest fuel stocks in typical forests in Kyiv Polissya zone of Ukraine on the example of the Boyarka Forestry Research Station.
Materials and Methods
The study was conducted in accordance with standard pyrological methods (Sofronov 2005, Kurbatsky et al. 1970). Forest fuel stocks were determined by the methods of full selection from discount plots of 1 ? 1 m and their weighing after the drying of the selected samples in a drying chamber to a bone-dry humidity at 105°C. Samples were selected in the typical sites in the stands, within the projection of tree crowns, at a distance of at least 0.25–1.00 m from the tree trunks depending on the age of the trees. The forest litter was studied during its stabilization in August and September.
Results
The stocks of forest fuels were determined in pure pine stands in the fresh fairly fertile and fairly infertile forest site types. The growth of stocks of forest fuels with increasing the age of pine stands was uneven, especially in the fresh fairly infertile sites. The main reason for this effect was the differense in the mensuration characteristics and as a result, it caused data heterogeneity. An increase in the stock of forest fuels with the age is due to the growth of the tree stand and an increase in the stock of needles in the crown of a tree. There is also the slowing of litter and duff decomposition rate. The last is explained by the change in the reaction of the soil environment due to its gradual acidification after the fall of the needles that comes annually and its decomposition The largest proportion of needles was detected in young 15-year-old pine stands. The maximum value of the litter stock in the fresh fairly fertile type of forest was observed at the age of 30 years (over 9 tons per ha); in the fresh fairly infertile site type, it was detected at the age of 90 years (over 13 tons per ha). Minimum stocks were found in pine stands that growing in the fresh fairly fertile site type at the age of 80 years (more than 2 tons per ha), and in the fresh fairly infertile site type at the age of 23 (more than 3 tons per ha).
The thickness of the litter layer tended to gradually increase with aging. The smallest thickness and probably faster burning during the study were noted at a young age, namely at the age of 15 years in the fresh fairly fertile sites, just only 2 cm, and at the same age in the fresh fairly infertile site type, 3 cm. At the same time, the thickest layer of the litter for the fresh fairly fertile type of forest was observed for 45–60 years and it was 6 cm. At the age of 80, the thickness of the forest litter of the first group (with small particles up to 6mm in size) tended to decrease and was up to 5 cm. In the fresh fairly infertile site conditions the greatest thickness of the layer of the litter was found in the mature pine forests of 70–90 years old; its thickness was 7 cm. At the age of 90 years, the thickness of the litter layer decreased to 5 cm.
Conclusions
The stocks of forest fuels increased with the age of pine stands. The stands with a relative density of stocking of 0.7 and more tended to accumulate the forest fuels having a wood particle size up to 25 mm in diameter. Large stocks of the litter and other forest fuels were found in fresh fairly infertile pine site type, which is explained by the longer decomposition time for the litter. In the mixed stands with deciduous trees, the stocks of the litter and duff were smaller. Here, the small amount of the litter of deciduous species also was noted improving the rate of decomposition of the total forest litter and yet reducing total forest fuel stocks.
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