The effects of climatic conditions and forest site types on disintegration rates in Picea abies occurring at the Modrava Peat Bogs in the Šumava National Park

Abstract

A survey of mountain spruce stand development in the Šumava National Park on Modrava peat bogs on an area of 1,370 ha resulting from spruce bark beetle outbreaks was performedby means of visual evaluation of aerial photographs from the period 1991-2000. In addition, our study addressed the influence of climatic effects (period1984-2000) andthe effect of forest site (climax, waterloggedandpeaty spruce stands) on the dynamics of disintegration of forest stands. We showed that new infestations were predominantly foundat short distances from their source, the average value was estimatedto be 40-60 m, whereas the longest distance for annual progress in west to east direction was estimated to be 120 m. Differences in the dynamics of disintegration between waterlogged stands and drier stands were confirmed. There was a positive relationship between the average temperature in the 2nd quarter of monitoring years which was registered as the period of the onset of bark beetle development and the proportion of degraded area in Norway spruce stands. Moreover, pronounced winter desiccation in January 1993 was a triggering mechanism with crucial importance for the outbreak of bark beetle in the studied area.