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Abstract
Introduction
About 1 million hectares of pine stands were established on formerly arable land. During 1950–1970s, most of the forests were pure and susceptible to root rot disease caused by the fungus Heterobasidion annosum (Fr.) Bref. By 2009, the area of pine stands weakened by pathological processes had made about 100 thousand hectares. One third of them were infected by the root rot. Thus, over the past 20 years the pathological process dynamics in Kharkiv Region has shown that the main factor of the deterioration of pine stands was the root rot. An uneven distribution of pathological processes in pine stands infected by the root rot significantly affects their growth and development. Root rot damage reduces stand productivity, deteriorates tree health, decreases the stock volume, and increases windfall.
The aim of the study was to determine the dynamics of mensuration characteristics, productivity and health condition in fragments of pine stands infected by Heterobasidion annosum.
Materials and Methods
The study was carried out in Forest-Steppe within Kharkiv Region, based on the data from 70 sample plots laid out in pine stands of III–X age classes, established on formerly arable land. The forest site type was fresh fairly infertile pine site. The sample plots were established according to the generally accepted forestry approaches: standard plots were established inside the decline foci as well as outside the foci in sites with single dying trees; circular plots were laid out outside the foci in the sites without signs of the disease (standard part). Tree height was determined in 15–25 trees. The health condition of the trees was determined according to the Sanitary Forest Regulations in Ukraine.
Results
According to the data from the sample plots, the forest inventory indices of pine stand fragments were found to be lower in the decline foci as compared to those outside the foci and in the standard part outside the foci. The pine stands infected by root rot have a high site class (I–Ic). Our results demonstrated that trees growing outside the decline foci have better growth rates than the trees growing inside them. As the root rot affects the trees, their heights in the stand fragments change. Furthermore, due to the different soil conditions, a diameter of trees in the infected parts of the pine stands increases more intensively at a young age. The health condition index of the stand fragments was 3.1 ± 0.08 in the disease foci and the trees there were strongly weakened. The health condition indices outside the foci were 2.7 ± 1.13 and 2.5 ± 0.5 in the standard part outside the foci; the trees were assessed as weakened.
Conclusions
The health status of trees in the affected part of the pine stands (root rot site) was assessed as weakened or dying: the health condition indices were 2.0–3.7. Outside the decline zone, the health condition indices were 1.8–3.4. The trees in the intact part of the stand (i. e. the standard part outside the foci) had weakened or severely weakened health status: their health condition indices were from 2.1 to 3.0. The dynamics of stand density showed that the number of trees inside the root rot site in the pine stands of III–X age classes was 24–50% less than for standard zone. Also, it was 1–31% less than the number of trees outside the root rot site. Both the average height and average diameter of trees inside the decline site were lower compared to those outside the decline zone (by 1.6% for the height and 1.8% for the diameter) and in the standard zone (by 5.2% for the height and 3.7% for the diameter). The differences in the average tree heights and diameters increased among the stand fragments with aging. The age dynamics of the stock volumes inside and outside the decline root rot site indicates that the greater the increase in a diameter outside the root rot site, the less the increase in a diameter inside it.
6 Figs., 20 Refs.
Key words: Heterobasidion annosum, stand characteristics,stand density, growing stock.