PREDICTION FOR BARK BEETLES CAUSED DESICCATION OF PINE STANDS

Abstract

Introduction

In recent years, forest desiccation has been registered in many regions, including Ukraine, where the decline of Scots pine (Pinus sylvestris L.) covered almost all Polissya. Tree mortality often occurred after the infestation by stem insects together with pathogens, which they vector. Two species of bark beetles have predominantly spread. They are pine engraver beetle Ips acuminatus (Gyllenhal, 1827) and six-toothed bark beetle Ips sexdentatus (Boerner, 1767) (Coleoptera: Curculionidae: Scolytinae), which have at least two main generations per year as well as sister generations. Prediction of bark beetles spread is based on understanding their preferences for environmental conditions connected with forest site conditions, forest age, tree species composition, the relative density of stocking, etc. In 2014–2017 we studied spatial dynamics of bark beetles caused desiccation in the State Enterprise “Teteriv Forest Economy” and revealed the characteristics of stands, which are the most favorable for bark beetles. Clear-cuts with wood debris and weakened trees around the perimeter were the preferred places for bark beetles.

The aim was to develop and to test an algorithm for predicting the spread of bark beetles caused desiccation on the example of Teteriv Forestry of the State Enterprise “Teteriv Forest Economy”.

Materials and Methods

The research was carried out in 2014–2017 in the stands of Scots pine in the State Enterprise “Teteriv Forest Economy”, Kyiv region. Changes in forest decline were studied on the base of monitoring data of forest health condition and of selective and clear sanitary felling in the stands. To evaluate the threat of bark beetles caused desiccation, data on forest fund, especially on the pine stands area, were taken from the forest inventory database as of 2014. Reliability of prediction of the threat of bark beetles caused desiccation was evaluated as a percentage of common subcompartments in two sets of subcompartments (with observed and predicted foci of bark beetles caused desiccation) from the number of compartments with actual foci of bark beetles. Spatial analysis of forest decline “spots” distribution was carried out using QGIS 2.18 (QGIS Development Team 2017).

Results and Conclusions

Using the set of parameters, namely proportion of pine in the forest composition, stand age, the relative density of stocking, stand origin and forest site conditions, makes it possible to reliably identify subcompartments with a high threat of bark beetles caused desiccation.

Pine proportion in the forest composition and its age has the greatest importance for prediction the threat of bark beetles caused desiccation in pine stands.

The relative density of stocking by itself is a less important risk factor than its sudden decrease.

Prediction accuracy increases if we consider the bordering of compartments with clear-cuts after main felling and clear sanitary felling.

Using the simplified scale (of four points and two main parameters) gives the possibility to recognize the trend of foci area dynamics or to compare it for administrative regions or natural zones.

Confinement of bark beetle foci to specific subcompartments can be predicted by GIS tools using the suggested algorithm, forest inventory database and digitized maps.

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