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Abstract
Introduction
The problem of forest fires is extremely relevant for Ukraine and for the world. Successful prediction of the occurrence and development of fires is possible only with a clear assessment of the structure of the forest litter and duff, which are among the main components of forest fuels. The study of characteristics and features of forest litter formation will enable to predict more accurately its ability to combustion.
Materials and Methods
The object of the study was the litter in Scots pine forests in Ukrainian Polissya. The stocks of the litter were determined in pine stands not damaged by fires in northern and southern parts of the Rivne Polissya. In general, 11 sample plots (SP) were investigated in pure pine plantations of different ages. The stocks of the litter were estimated by fractions according to Rodin's method (Rodin & Bazievich 1965) in three organic horizons: the upper, litter – L; the middle, fermented – F and the lower, humic – H. The litter layer density was determined according to Kurbatsky's method, as the ratio of the stock of litter to the thickness of its layer.
Results
The stock of the litter increased with age of planting (r = 0.87; p = 0.05). Regression analysis revealed that 76 % of the litter stock was determined by its thickness (R? = 0.76; p = 0.05). Humidity in different layers of forest litter varied considerably. The lowest humidity was observed in the litter horizon L, which dries out the fastest. Layers F and H were wetter; it is characteristic that the bottom layer did not always have the highest humidity. One can assume that, on the one hand, for a small amount of precipitation due to the high density of the middle layer F moisture does not enter the deeper horizons. On the other hand, in this type of forest, horizon H was strongly permeated with roots of Scots pine and roots of the ground cover, which actively absorb moisture retained in this layer. Correlation dependence between the litter density and the age of the forest stand, which has the coefficient r = 0.73, was revealed. During the regression analysis, it was found that this dependence is approximated by the equation of y = 0.7458x + 15.47. The difference in litter density between different age classes may be significant. So, if in pine stands of 2nd–3rd age class the average density of the litter was 30.6–36.2 g·dm-3, then in 6th–7th age class the value was 74.8–97.3 g·dm-3, that is, it grew by 2.1–3.2 times. It has been established that there was a significant increase in the stocks of the middle and lower layers in pine stands after 50 years, which, in the conditions of prolonged drought and the occurrence of a surface fire, would pose a serious threat to the stand.
Conclusions
The Scots pine stands of Rivne Polissya have accumulated significant stocks of litter (from 11,700 to 86,200 kg·ha-1). In the pine forest, the distribution of the litter was found to be uneven: the largest volumes were registered near the tree trunk, and they decreased with the increase in distance from it. With increasing age of pine plantations, both the volumes and the density of the litter increased. The density of forest litter increased from 30.6 to 97.3 g·dm-3 for age classes from 2nd to 8th. Up to 50–60 years, the maximum density value was usually registered on the edge of the crown canopy, and in the older pine stands, near the trunk. During ontogenesis of pine forest stands, the ratio of forest litter stocks between the organic horizons has changed significantly. After 50 years, the proportion of F and H sharply increased.
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