The factors behind spruce resistance to bark beetle attack

Nataliya Korolyova

Doctoral thesis

Abstract:

Forests in the Northern Hemisphere experience severe climate change intensified insect outbreaks. This study focuses on Norway spruce (Picea abies) resistance to Ips typographus attacks, aiming to unveil the factors influencing tree survival during bark beetle outbreak in Central Europe. To investigate tree survival mechanisms, we used a multidisciplinary approach based on analytical chemistry, dendroecology, and remote sensing methods. To quantify tree survival responses, machine learning techniques and non-linear logistic regression models fit in likelihood framework were used. Two beetle-disturbed areas located in the Bohemian Forest and Vosges mountains served as study sites, employing experimental and observational approaches to explore tree defence mechanisms and life-history trade-offs. We hypothesised that tree survival is a non-random process governed by external and internal factors. To study tree chemical defence mechanisms, we conducted a Methyl jasmonate (MJ) inoculation experiment and mechanical wounding experiment. To discern tree life-history trade-offs in the allocation of limited resources, the radial growth rates prior to disturbance were compared among surviving and reference trees. These rates were also used to reconstruct disturbance in the Bohemian Forest area. We used remotely sensed Landsat 5, Google Earth Pro historical imagery and field data to estimate stand density prior to the outbreak. We found that tree survival is a non-random process driven by multiple external and internal factors and their interactions. The probability of spruce survival is positively and non-linearly associated with the proximity to previously attacked hosts, catechin production, self-shading and long-term climatic water balance. Survival probability has negative non-linear relationships with tree size, stand density prior to an outbreak, stem sun-illumination and crown defoliation. Climatic water balance interacted with stand and tree-level factors, aggravating the negative effects of stand density and tree size, and enhancing the positive effects of self-shading and moisture availability on tree survival. Surviving trees exhibited slower radial growth than reference trees in decades preceding the outbreak (p<0.05). Although we did not identify any differences in the whole terpene profiles between LTS and reference trees, as shown by untargeted gas chromatography – mass spectrometry, surviving and references trees varied in the abundance of individual compounds prior to and after MJ inoculation. Our findings enhance understanding of Norway spruce survival mechanisms during bark beetle outbreaks, suggesting potential heritability of resistance traits. Maintaining surviving individuals in post-disturbance areas and incorporating them into tree breeding programs could improve forest resilience, but further research on genetic and chemical factors across diverse environments is crucial for a more comprehensive understanding.

Keywords

tree survival, Ips typographus, Picea abies, tree resistance, Last Tree Standing, bark beetle outbreak, forest disturbance, phenolics, terpenes, growth rates, chemical defence, self-shading, insolation, drought, climate change

Language used: English

Date on which the thesis was submitted / produced: 11. 2. 2024

Thesis defence

• Supervisor: prof. Ing. Marek Turčáni, PhD.
• Reader: Tomáš Hlásny, prof. RNDr., PhD., Petr Doležal, Ing., externi, Pavel Mezei, externi

Czech University of Life Sciences Prague

Faculty of Forestry and Wood Sciences

Doctoral programme / field:
Forestry Engineering / Forest Protection and Game Management