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Abstract
Introduction
An intensive urbanization enhances the negative impact of the complex of anthropogenic factors on forests, which leads to the forest deterioration, thinning, and reduction in productivity. Fires are particularly dangerous for the forests of the Kharkiv urban green belt. Fire damage to the trees worsens their condition, and untimely cleaning after fire causes the outbreaks of pests and diseases. As a result, the forestry sector sustains significant losses, both direct and indirect. This article succeeds and complements the research of laboratory of forest ecology of Ukrainian Research Institute of Forest and Forest Melioration on the tendencies of fires in the green belt of the city of Kharkiv, as well as on changes in the condition and development of pine forests after fires of various intensities.
Determination of losses from forest fires should be based on the comparison of actual productivity with the potential one.
Materials and Methods
Pyrogenic changes in the productivity of pine forests were investigated on the example of State Enterprise “Zhovtneve Forest Economy”, which had the largest proportion of fire incidents not only in the green belt but throughout the all Kharkiv region.
The forest fire tendencies were analyzed using the fire database formed on the basis of the incident records of the state enterprise for the period from 1989 to 2016. The pyrogenic impact was estimated both by the absolute number and area of fires during an average year and by the ratio of total area of forest fires to the total forest area, equivalent to 1000 hectares of the area.
As a material for analysis, the data of electronic subcompartment database of Production Association “Ukrderzhlisproekt” were used as on 2006. The database covers 1,500 subcompartments with a total area of 5.9 thousand hectares, accounting for 78 % of all pine forests in the state enterprise.
Growing stocks of modal pine forests in certain forestries and areas with different pyrogenic impact were compared to that of standard pine forests. The efficiency of use of forest growth potential was determined by methods of forest typological analysis.
Results and Conclusions
The maximum number and area of fires in the forests of the Kharkiv region was in the State Enterprise “Zhovtneve Forest Economy” (139 cases in an average year, with a total area of 22 hectares).
The particularly acute pyrogenic situation was noted in Vasyshevske, Babayivske, Merefyanske and Rokitnyanske forestries of this forest enterprise. For the period from 1989 to 2016, the highest number of fires had been recorded in Babayivske and Vasyshevske forestries (an average of 36.1 and 45.3 cases per year). In these two forestries, the area of the fire damage was also the largest: 2.7 and 4.3 ha per year, respectively.
Pine stands, which had the highest burning index class, were the most affected by fires. In forestries with the highest number of fire incidents, the proportion of pine trees was from 20.3 to 46.0 %. In other forestries with a minimum number and area of fires, the area of pine trees was 1.8–3.5 % only. In forestries with the highest number of fires, infertile and fairly infertile pine sites amounted to more than 90 % of the area, and the percentage of dry infertile and fairly infertile pine sites was insignificant. As the area of forestries and the percentage of pine stands in them were different, the risk of fires was better to be estimated by the ratio of total area of forest fires to the total forest area. This indicator was much higher in Vasyshevske and Babayivske forestries as compared with other forestries.
The highest numbers were recorded in the area of Babayevske forestry, and the smallest ones in the Bir area of Vasyshevske forestry. The fair danger level varied from the “above the average” (Bir and Bir-2) to the “emergency” (Vashchenkivsky Bir).
Although the proportion of fires in particular areas ranged from 35 to 73 %, in some years the fires in them reached almost 100% of the total number and area.
The distribution of pine stands by age classes differed in forestries with the highest number of fires. In fresh fairly infertile pine site type, which is predominant, pine stands of all age classes were presented. The especially fire-dangerous fresh infertile pine site type was much less outspread and was represented not by all classes of age.
There was a significant decrease in the stand density and in site class in the pine stands of Babayivske forestry, having the highest fire danger. The lowest average density (0.67) was recorded for Vashchenkivsky Bir area. In the maturing and mature pine stands in this forestry, the density was reduced to 0.3 at the age of 100–110 years. Pine trees of the age class III of the Babayivske forestry have the lowest site class, III, 4.
Comparison of values for the stock of standard and modal tree stands allowed indicating their maximum possible and present productivity. The stock of modal pine stands was increasing up to 90 years old. In older plantations, a significant decrease was recorded. At the same time, the growing stock of standard stands far exceeded the values of modal stands in the forestries.
The lowest average stock was found in Babayivske forestry. The growing stock of 20–30-year-old pine stands was several times smaller than that in other forestries. Somewhat lower decrease at this age was in Vasyshevske forestry.
The highest growing stock of modal pine stands of VIII and IX classes was in the Merefyanske and Rokitnyanske forestries (from 399 to 436 m3?ha-1), where the ratio of total area of forest fires to the total forest area was the smallest. However, even there, the deviation from the standard stands in certain age classes in “Zhovtneve Forest Economy” might exceed 50 %. The highest difference (more than 80 %) was determined for the pine stands of age classes II and III in Babayivske forestry. In the middle-aged and maturing stands, these values did not exceed 38 %.
The difference in stocks between modal and standard pine stands of some areas was even greater. The minimum stock of modal pine stands was recorded for most of the age classes for Vashchenkivsky Bir forest. In this area, there was a very low stock for trees up to 30 years old and a sharp decrease in the stock for mature and overmature pine stands.
Comparison of growing stock for modal pine stands with that for the standard ones in the forest economy allowed determining the rate of forest growth potential use with different forest fires impact. Thus, the lowest growth potential rate for almost all the age classes of pine stands was found in Babayivske forestry, which has the highest average number and the largest areas of fires per year. The smallest values were observed in young and mature pine stands, that is, such stands can be more significantly affected by fires. This value was the least different at the age of 40 years for all forestries.
4 Figs., 6 Tables, 12 Refs.