Genetic diversity among populations of forest tree species enhances their capacity to adapt to climate change

Current climate change is having an increasingly negative impact on the environment, particularly on forest ecosystems. Within these stressed ecosystems, different tree species exhibit various defence mechanisms and reaction speeds to environmental challenges. The least resilient individuals, unable to withstand external pressures, gradually perish, leading to natural selection within the affected population.

Photo: More resilient individuals survive among the dry pine trees; author Jan Řezáč

To save a surviving tree after a bark beetle disaster, careful procedures must be followed to ensure the tree continues to thrive and that its surrounding environment is restored.

Surviving trees play a crucial role in forest recovery after a disaster. They can provide a source for a new generation of trees and help maintain biodiversity. In the long term, the presence of these trees is essential for the natural recovery of forest ecosystems.

In practice, however, all trees—including those that are resistant to damage—are often cut down in areas affected by a disaster. If a tree is resistant to adverse effects and does not spread harmful organisms, cutting it down is an unnecessary loss. Preserving these trees allows for the collection of valuable reproductive material, which can lead to the growth of a more resilient forest generation.

Photo: A surviving beech at the edge of a clearing serves as a source of seeds for natural regeneration; author Jan Řezáč

While working on the project NAZV QK22020062 titled “Identification of Surviving Individuals of Forest Tree Species in Disaster Areas: Their Rescue and Research into Their Resistance” (Identifikace přeživších jedinců lesních dřevin na kalamitních plochách, jejich záchrana a výzkum jejich rezistence), scientists from VÚLHM, v. v. i., developed a certified methodology Metodické postupy vyhledání a záchrany rezistentních druhů domácích dřevin. This methodology outlines the procedural steps for searching for and rescuing resistant species of domestic tree varieties.

The proposed methodological procedures aim to identify and utilise tree species that demonstrate resistance to both abiotic and biotic harmful factors in forest stands. Resistance is assessed by examining areas of the forest affected by calamities, where, among the many dying trees, there may be individual trees or groups that are of high quality and resistant.

The resilient trees or stands that are identified can serve as sources of reproductive material for forest tree species (RMLD). This material can take the form of natural regeneration stands, sources of seeds, or even seedbeds established from resistant clones. The methodology also includes a classification system for identifying resistant trees or parts of stands, and outlines processes for recognising them in forestry practices.

Photo: A group of silver firs that are suitable for natural regeneration; author Jan Řezáč

Plant resistance refers to a plant’s ability to survive and thrive in the face of adverse conditions, including pests, diseases, drought, frost, and environmental pollution. This resistance is influenced by a combination of genetic traits, physical and chemical defence mechanisms, and the ability to adapt to changing environmental conditions.

In forestry, researching and breeding resistant tree species is a complex task, particularly due to the longevity of forest tree species, and this field is still in its early stages.

Currently, under the pressures of climate change, significant commercial tree species are facing increasing damage. Changes in temperature and water availability, along with a rising population of bark beetles (accelerated by higher temperatures), have weakened tree defences and placed trees under significant stress.

Moreover, these environmental changes are facilitating the spread of invasive species and harmful organisms that previously occurred only in limited regions.

Coniferous tree species are particularly vulnerable, often experiencing critical situations. For instance, damage to Scots pine from bark beetles increased eightfold between 2010 and 2019.

Photo: Beech bark beetle digging a chambre; author Adam Véle

In some areas, beech and fir tree species were found to be dying in 2020 due to a significant increase in the number of bark beetles. These pests, which were previously monitored in minimal numbers and considered secondary threats to these tree species (such as the beech bark beetle /Taphrorychus bicolor/), have now become a bigger concern.

Although European beech trees have strong regeneration abilities, they struggle to withstand the increasing pressures they face. Efforts are being made to enhance the presence of beech in forests typically dominated by silver fir. However, climate change, combined with high pest pressure, has significantly slowed or even prevented the return of beech to these forest environments.

In regions of the Czech Republic most affected by bark beetles, where entire stands of trees have died or are dying, some resilient individuals have managed to withstand this high pest pressure. The specific mechanisms that enable these trees to endure such conditions are not yet fully understood, as existing knowledge is too general to pinpoint the causes. It is important to note that even healthy trees cannot survive severe bark beetle attacks, suggesting that resistance may be linked to the varying production of volatile substances that beetles use to locate their host trees.

Photo: Locality Buková hora; author Jaroslav Dostál

Scientists in the Czech Republic studied both infected and healthy individuals of selected forest tree species directly in their natural habitats. The findings revealed that Scots pine responded to bark beetle attacks differently than Scots beech and silver fir. The most significant changes in phytohormones were observed in pine, while beech and fir exhibited the largest alterations in photosynthetic pigments.

The varying resistance of different tree species to bark beetle infestations may be attributed to genetically determined traits. The adaptive capabilities of these species are shaped and enhanced by the gradual development of populations and natural selection under diverse environmental conditions. A stable and ample genetic diversity, which includes potentially beneficial alleles, is essential for this process.

The level of genetic diversity within forest tree populations plays a crucial role in their ability to adapt to climate change. In the face of changing environmental conditions, it is vital to maintain high intra- and inter-population variability within tree species. For instance, a genetic study of surviving spruce trees from the Šumava region revealed that genetic diversity is one of the most important factors in tree defence mechanisms.

The paper Metodické postupy vyhledání a záchrany rezistentních druhů domácích dřevin (Methodological steps for searching for and rescuing resistant species of domestic tree varieties) can be downloaded here.

Authors: Ing. Martin Fulín, Ph.D., RNDr. Adam Véle, Ph.D., VÚLHM, v. v. i., e-mail: fulin@vulhm.cz

Prepared by Ing. Jan Řezáč, VÚLHM, v. v. i., email: rezac@vulhm.cz

Introductory photo: Several live spruces in an already dry stand. Author: Jan Řezáč