Weather conditions and host characteristics drive infestations of sessile oak (Quercus petraea) trap trees by oak bark beetles (Scolytus intricatus)

Abstract

The European oak bark beetle (Scolytus intricatus) has the potential to impact forest structures through its selection of certain trees. We investigated potential S. intricatus colonisation densities by setting up 150 trap trees and analysing them in 5-metre sections during a three-year period from 2014 to 2016 in a temperate forest in Slovakia, Central Europe. Understanding the population dynamics of S. intricatus and the drivers of its colonization density on trees is necessary if attempts to control or manage populations of S. intricatus in managed forests are to succeed.To explain the population dynamics of S. intricatus, ANOVA was used to assess the colonisation densities in the stem , and generalized linear mixed effect models (GLMMs) were used to analyse the main characteristics of the host trees and the meteorological variables. Structural equation modelling (SEM) was then used to explain the multitude of relationships among the predictor variables and bark beetle populations.Scolytus intricatus reached higher population levels under dry and warm conditions, when trees were prone to drought stress. The highest colonization densities at the trap trees occurred in May and June of 2014 and 2016; in 2015, the highest densities were reported in August and a second generation of S. intricatus was observed. This is unusual, as this species is usually univoltine, i.e. has one generation per year under Central European conditions.Population levels differed in different months during the 3-year study period, i.e. patterns of population dynamics and phenology are not repeating. The mixed-effects models demonstrated that the seasonal temperature influenced the occupation of trap trees by S. intricatus and that the lengths of the galleries were affected by the section surfaces.We conclude that environmental stress hastens the rate of drought stress in oak trees, resulting in faster population growth and higher survival of S. intricatus.