A predictive framework to assess spatio‐temporal variability of infestations by the European spruce bark beetle

Abstract

Natural disturbances are key factors for the development of forest ecosystems. In forests of central Europe and Scandinavia, the European spruce bark beetle Ips typographus is the most devastating biotic disturbance agent in Norway spruce Picea abies, but our understanding of the factors determining its spatio‐temporal dynamics is still quite limited. To quantify the drivers of bark beetle dynamics, we analyzed a survey dataset with annual resolution that covers 17 yr and 469 forest districts (10 860 km2 of forest area) all over Switzerland. We used Poisson log‐normal models in a Bayesian framework to analyze the spatio‐temporal dynamics of bark beetle infestation spots at the forest district level. Bark beetle infestations increased with increasing heat sum (> 8.3°C), volume of standing Norway spruce stock, and the number of infestation spots of the previous year. Precipitation tended to slightly affect the risk of bark beetle infestations. Two major storm events further increased the spatio‐temporal variability of bark beetle infestations. Spruce abundance, storm damage and temperature are known to be important factors influencing the population dynamics of the European spruce bark beetle. Our study is the first to quantify the combined effects of spruce abundance and heat sum, whereby the heat sum turned out to be the most important and consistent predictor. Because our study area encompasses large ecological and climatological gradients, our model is likely to be applicable to Norway spruce forests in other regions of central Europe and Scandinavia.

Climate drivers of bark beetle outbreak dynamics in Norway spruce forests

“…Years with warm summers were generally characterized by an increase in timber loss. Warmer summer temperatures generally reduce bark beetle development time, increase performance and fitness, and are therefore expected to increase population impacts on forests (Bale et al 2002, Jönsson et al 2009, Stadelmann et al 2013a, Bentz and Jönsson 2015. In our study the effect of warm temperatures was positive across South and North Europe, confirming the high plasticity of I. typographus in response to temperature variations (Dolězal and Sehnal 2007).…”

“…Similarly to other bark beetle species, controls of I. typographus populations. Our results suggest that greater efforts should be made to integrate temperature warming, drought and storm effects into future scenarios of bark beetle outbreaks under global change (Seidl et al 2009, Stadelmann et al 2013a, Temperli et al 2014 as their effects are not always additive. In particular the positive effect of warming temperatures was important only when no other abiotic triggers were present.…”

“…Warmer summer temperatures generally reduce bark beetle development time, increase performance and fitness, and are therefore expected to increase population impacts on forests (Bale et al 2002, Jönsson et al 2009, Stadelmann et al 2013a, Bentz and Jönsson 2015. Years with warm summers were generally characterized by an increase in timber loss.…”

Tree and stand-level patterns and predictors of Norway spruce mortality caused by bark beetle infestation in the Tatra Mountains

“…These results correspond to landscape-level analyses on the role of topography, which suggest that south-facing forest edges are more stressed and south-facing trees are killed sooner and more frequently during outbreaks (Powers et al, 1999;Jakuš et al, 2011;Kautz et al, 2013). Moreover, bark beetle larvae develop much faster on warmer, sun-exposed south-facing slopes, resulting in more generations produced per year (Stadelmann et al, 2013). In the case of the late 2000s-2014 outbreak that spread across the study area, it is likely that initiation occurred at lower elevations and spread rapidly northward through larger, weakened trees in our plots.…”

Transition from windfall- to patch-driven outbreak dynamics of the spruce bark beetle Ips typographus

“…At the local level the risk of bark beetle infestations is generally considered to be a function of site/stand characteristics and local beetle pressure (Shore and Safranyik, 1992;Lausch et al, 2011;Stadelmann et al, 2013b;Withrow et al, 2013;Kärvemo et al, 2014b). The process by which new infestation patches are formed is not fully understood, even though a comprehensive literature including experiments and field studies indicate that the spatial pattern of infestation patches across the landscape is determined by beetle dispersal and colonization behavior, beetle host preferences, stand conditions and chemical interactions between trees and beetles (Netherer and Nopp-Mayr, 2005;Boone et al, 2011;Zhao et al, 2011;Schiebe et al, 2012;Hilszczanski et al, 2006).…”