Persisting bark beetle outbreak indicates the unsustainability of secondary Norway spruce forests: case study from Central Europe

Abstract

• Context Secondary Norway spruce forests in the Western Beskids are among the most damaged forests in Europe. Although spruce bark beetle (Ips typographus) has been recently causing large-scale damage to these forests, our understanding of I. typographus dynamics in this environment is inadequate for evaluating forest sustainability. • Aim This study aims to evaluate the patterns of damage caused by I. typographus to spruce forests with compromised ecological stability. • Methods Forest infestation by I. typographus was inferred from sanitary felling data collected from 1998 to 2004. Stand and site data were obtained from forest management plans. Spatial-dependence analysis, ordinary kriging and neural network-based regression modelling were used to investigate the patterns of infestation and the casual relationships in the studied ecosystem. • Results I. typographus long-distance dispersal substantially decreased with outbreak culmination. The spread of infestation was only weakly related to stand and site parameters. Infestations spread isotropically at the stand and patch level but directionally at the regional scale. • Conclusions The large-scale spread of infestation can be explained by the uniform age and species composition of the investigated forests and by the ability of populations to overwhelm suboptimal trees. The observations presented here suggest that secondary spruce forests in Europe may be unsustainable due to unprecedented bark beetle outbreaks, which can be further amplified by changing climate.

Forest ecosystem services affected by natural disturbances, climate and land-use changes in the Tatra Mountains

“…A further massive impact on the remaining forest at the treeline is expected in the following years. These findings support the predictions of Hlásny & Tur<áni (2013) and Hlásny et al (2014) on the limited sustainability of Norway spruce forests in Central Europe associated with a climate change impact on spruce forest in the entire Carpathians.…”

Effect of different tree mortality patterns on stand development in the forest model SIBYLA

“…This is, however, not a realistic assumption because various transitions between random and patchy tree mortality patterns are typical of bark beetle population dynamics. Typically, small populations generate a scattered pattern because the beetles search for suitable hosts, while beetles in large populations tend to infest the trees in a closer vicinity (Kausrud et al 2011;Hlásny & Turčáni 2013). Large populations might tend to collapse after a several-year period of the outbreak culmination because of the effect of diverse density dependent regulation mechanisms (Raffa et al 2008).…”

“…The literature review indicated that under high beetle densities (epidemic phase) most of beetles disperse over short distances (up to 100 m), and the dispersal (or the appearance of new infestation spots) disappears within 500 -1,000 m from old infestations (Wichman & Ravn 2001;Kautz et al 2011;Hlásny & Turčáni 2013;Stadelmann et al 2014). Therefore, we modified the RUN algorithms so as we define the affinity of the newly infested trees to the trees infested in the previous period.…”

“…Berec et al 2013). Bark beetle-related tree mortality is a highly complex process that is driven by both the host susceptibility, bark beetle population size and diverse environmental perturbations (Wermelinger 2004;Hlásny & Turčáni 2013). Interactions between the host *Corresponding author.…”

“…Jiří Trombik, e-mail: trombik@fld.czu.cz tree distribution, tree susceptibility and density-dependent bark beetle dispersal capacity, generate specific patterns of infested trees. Such patterns might range from the scattered occurrence of infested trees, which is typical of small beetle densities, to patchy and even a large scale infestations that typically occur when the populations are in the outbreak phase (Hlásny & Turčáni 2013). Because tree mortality patterns might affect stand structure and the quality of ecosystem services in the period following the infestation, it is desired to include such information into forest models, which operate at a scale of trees.…”