Influence of selected factors on bark beetle outbreak dynamics in the Western Carpathians

In the period from 1992 to 2013, more than 3.8 million m³ of spruce wood from an area of 55 thousand ha of forests in the Kysuce region (Western Carpathians) was affected by bark beetles. This region has had the highest volume of salvage fellings in Slovakia. While before 1991, bark-beetle outbreak usually occurred after snow and wind disturbances, since 1992 they have occurred in the years with extremely warm and dry growing seasons and the years following them. These years were also characterised by high volumes of wood affected by honey fungus (Armillaria spp.), which only rarely took part in the calamities before 1992. Extreme deterioration of the situation occurred after 2003. In fragmented and sparse stands, the volume of wood damaged by wind increased. Artificial origin of spruce stands, their high occurrence, high age and even-agedness are likely pre-disposing factors of spruce forest decline. Bark beetles have become the most important factor of spruce decline. The most important factors driving the bark beetle attack on forest stands in the period 1973–2013 were the amount of unprocessed wood in the previous year; the amount of wood affected by honey fungus, precipitation total, and average temperature in the current growing season. Another important factor that complicated the situation was also the inferior quality of forest management.