Drivers of Spruce Bark Beetle (Ips typographus) Infestations on Downed Trees after Severe Windthrow

Abstract

Research Highlights: Bark beetles are important agents of disturbance regimes in temperate forests, and specifically in a connected wind-bark beetle disturbance system. Large-scale windthrows trigger population growth of the European spruce bark beetle (Ips typographus L.) from endemic to epidemic levels, thereby allowing the killing of Norway spruce trees over several consecutive years. Background and Objectives: There is a lack of evidence to differentiate how outbreaks are promoted by the effects of environmental variables versus beetle preferences of trees from endemic to outbreak. However, little is known about how individual downed-tree characteristics and local conditions such as tree orientation and solar radiation affect beetle colonization of downed trees. Materials and Methods: To answer this question, we investigated the infestation rates and determined tree death categories (uprooted, broken, and stump) in wind-damaged areas in Western Tatra Mts. in Carpathians (Slovakia) from 2014–2016, following a windthrow in May 2014. In total, we investigated 225 trees over eight transects. For every tree, we measured its morphological (tree height, crown characteristics), environmental (solar radiation, terrain conditions, trunk zenith), temporal (time since wind damage), and beetle infestation (presence, location of attack, bark desiccation) parameters. We applied Generalized Additive Mixed Models (GAMM) to unravel the main drivers of I. typographus infestations. Results: Over the first year, beetles preferred to attack broken trees and sun-exposed trunk sides over uprooted trees; the infestation on shaded sides started in the second year along with the infestation of uprooted trees with lower desiccation rates. We found that time since wind damage, stem length, and incident solar radiation increased the probability of beetle infestation, although both solar radiation and trunk zenith exhibited nonlinear variability. Our novel variable trunk zenith appeared to be an important predictor of bark beetle infestation probability. We conclude that trunk zenith as a simple measure defining the position of downed trees over the terrain can anticipate beetle infestation. Conclusions: Our findings contribute to understanding of the bark beetle’s preferences to colonize windthrown trees in the initial years after the primary wind damage. Further, our findings can help to identify trees that are most susceptible to beetle infestation and to prioritize management actions to control beetle population while maintaining biodiversity.

30-Year Changes in Oak-Hornbeam Forest after Windthrow

“…Nevertheless, local windstorms of moderate power causing the blowdown of single trees can influence forest structure in the long-term perspective and relatively quickly adjust it to the changing environmental conditions without causing a complete destruction that would initiate succession. Transformation of the stand begins with opening of numerous gaps [19] or initiation of the gap formation process that involves damage to branches or roots etc., further leading to the death of trees, e.g., due to outbreaks of bark beetle, which attacks weaker trees and kills them [3,5,7]. Small gaps provide conditions promoting the growth of underwood or initiate regeneration in sites where light availability used to be insufficient.…”

“…They are the main cause of live biomass loss in northern European forests [3]. Forests damaged by wind become susceptible to outbreaks of bark beetle (Ips typographus L.) and other engravers [3][4][5][6][7]. Strong winds also contribute to the formation of small and large gaps, semi-open and open areas [8,9].…”

“…Wind disturbance has been studied in temperate forest ecosystems, especially in North America [11][12][13][14]. Studies in Eastern Europe investigating this problem have focused mainly on mountain forests and poor habitats that cover the largest areas [2,7,[15][16][17][18][19][20]. Studies investigating long-term transformations caused by windstorms are gaining a new meaning in the light of climate change.…”

Ips sexdentatus Mass-Trapping: Mitigation of Its Negative Effects on Saproxylic Beetles Larger Than the Target

“…Due to favorable conditions, bark beetle outbreaks are alarmingly increasing, with a severe impact on European conifer forests [1][2][3]. In recent years, climate change has caused a higher frequency of extreme weather events, including windstorms and severe drought [1]. These disturbances increase the suitable breeding materials for bark beetles, such as stressed or uprooted trees [1].…”

“…In recent years, climate change has caused a higher frequency of extreme weather events, including windstorms and severe drought [1]. These disturbances increase the suitable breeding materials for bark beetles, such as stressed or uprooted trees [1]. Therefore, bark beetle population densities may rise and, during epidemic outbreaks, aggressive bark beetle species are able to move from stressed and weakened trees to healthy ones; this behavior was confirmed in the six-toothed pine bark beetle, Ips sexdentatus (Böerner) (Coleoptera: Curculionidae: Scolytinae) [4].…”