Growth, structure and condition of stands planted on clear-cuts after annosum-infected pine stands

Abstract

Introduction

In recent years, in Ukrainian Polissya, the area of pine forests affected by the root rot (Heterobasidion annosum (Fr.) Bref.) is steadily increasing. The largest foci of this disease are concentrated in planted pine stands subordinated to Chernihiv, Zhytomyr, Kyiv, Volyn and Rivne regional forestry and hunting management departments.

In Ukraine, root rot damage was mainly studied in first-generation pine stands created on formerly arable lands. There are only few works on how the root rot influences the mensuration characteristics, productivity and health condition of the second-generation stands of both Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth.) established on the clear-cuts after planted pine stands affected by the root rot.

The aim of the study was to compare stand parameters, productivity and health condition of the second-generation mixed pine stands established on clear-cuts after pine stands which were affected by Heterobasidion annosum.

Materials and Methods

The study was carried out in a mixed stand where Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth.) dominate, at the Koryukivske Forest Enterprise and Semenivske Forest Enterprise (Eastern Polissya, Ukraine).

Six sample plots were established in the decline foci where infected and dead trees were concentrated. Six sample plots were laid out as a control outside the decline foci in a relatively healthy part of the stands and one sample plot was established in the silver birch stand.

The age of the stands varied from 24 to 49. The stands are located in the fresh infertile pine site and fresh fairly infertile pine site.

The second-generation pine stands were planted on clear-cut sites after pine stands infected by annosum root rot. The following mixing patterns were used: 3 rows of Scots pine (Sp) and 1 row of silver birch (Sb), 5 rows of Sp and 3 rows of Sb, 3 rows of Sp and 2 rows of Sb, 3 rows of Sp and 3 rows of Sb, 2 rows of Sp and 8 rows of Sb. The stands were mainly planted with the 2.0 ? 0.5 m planting sites spacing.

The stands’ characteristics and their health condition were evaluated by means of generally accepted in forestry and forest mensuration methods. The health condition of the trees was assessed based on 6 categories (Sanitary Forests Regulations in Ukraine, 2016). The degree of stand damage was characterized by the health condition index I_c which was calculated according to the recommendations given by URIFFM experts.

The study data were statistically processed using the parametric and non-parametric analysis methods.

Results

It was established that according to the non-parametric Kolmogorov-Smirnov goodness-of-fit test (?), compared empirical populations of the trunk number distributed by their thickness depending on the average diameter of a stand in the root rot damaged sites and on control (non-damaged sites) belong to different parent populations and follow the different curves.

In the second-generation pine stands established on clear-cuts of the pine stands affected by the root rot, the losses of wood are higher than in the first-generation stands growing in similar conditions.

With age the stands’ density decreases significantly (by 15–62%), their relative density becomes lower by 0.12–0.59 units and their total standing volume becomes 15–59% lower due to pathological mortality as a result of the negative impact of root rot.

The volume of dead pine trees is 40–84% higher in the disease foci compared to that outside them due to the increase of infectious root rot background when re-planting pine stands in pathogen-infected areas.

Within the root rot foci, the trees with a significantly larger diameter (on average on 15–42% in comparison with the non-damaged sites) die off in the mixed young and middle-aged stands. It happens because in the decline foci not only depressed thin trees of IV and V Kraft classes die but also the dominant trees of I– III Kraft classes do.

In young stands up to 40 years old, the average heights and diameters of dead birch trees do not differ significantly in decline foci and control. However, this difference is statistically significant in middle-aged stands.

The number of birch trees within the decline foci is higher by 1–6 units compared to the control sites.

Conclusions

In the mixed second-generation pine stands, the density is 15–62% lower in the root rot damaged sites and the growing stock volume is 15–59% lower compared to those in controls due to pathological mortality.

The average diameter of living pine trees in the root rot disease foci differs by 12% in both – higher and lower – directions in comparison with the non-damaged sites. In the disease foci compared to control, on average 15–42% thicker trees die off.

In the second-generation mixed pine stands, the health status of the pines in the root rot foci is much worse (from “weakened” to “dying”) compared to control, where it is “weakened”.

The health status of the birch part of the stand is much better. In the root rot damaged sites, it varies from “healthy” to “weakened” and is “healthy” in control. Thus, birch trees have better viability in root rot foci.

6 Figs., 1 Table, 31 Refs.