The resilience of forests to climate change is intricately linked to their genetic diversity
Currently, the outlook for forest protection is promising. We have observed a continued decrease in bark beetle infestations, and damage from abiotic factors has been at its lowest level since 2014. In recent years, droughts have occurred more frequently during the second half of the growing season, a time when they have less impact on tree health, growth, and pest dynamics compared to the spring months.
Photo: The wounds from the bark beetle disaster are gradually healing, revealing a clearing filled with a diverse mix of tree species. Author: Jan Řezáč
“It is quite striking that, according to global data, the last eleven years have been the warmest since records began. The years 2015 and 2018 had a significantly negative impact on forest health. In contrast, since 2020, the onset of spring weather has generally been favourable from a forestry perspective. However, a warm and dry spring can weaken forest stands and quickly lead to an increase in bark beetle populations. Additionally, fluctuations in climate systems can cause significant abiotic damage due to wind or snow. While we cannot predict exactly when these events will happen, we can assume that they will occur at some point. Thus, the balance in nature remains fragile,” says Assoc. Prof. Ing. Vít Šrámek, Director of the VÚLHM.
How are our forests faring? New methods of protection and monitoring can help address emerging threats.
Data from the Forest Protection Service—covering approximately 70% of the total forest area in the Czech Republic—indicate that the volume of damage to woody plants has significantly decreased year-on-year, from 4.6 million cubic meters of wood mass in 2024 to 3.0 million cubic meters in 2025. Two-thirds of this damage was caused by abiotic factors, mainly wind and drought, while the remaining third was due to biotic factors. Interestingly, while damage to spruce trees decreased by approximately 45% compared to 2024, other coniferous trees, particularly pines and firs, faced increased attacks from bark beetles. Among deciduous trees, ash was also affected. The greater variety of insect pests and their differing biological characteristics are increasing the demands placed on forestry personnel.
Photo: Mixed forest with linden, beech, and hornbeam, which contribute to genetic diversity. Author: Jan Řezáč
In 2025, there was a significant occurrence of fungal pathogens affecting forests. The volume of wood infested with honey fungus approached nearly 25% of the volume infested by bark beetles on spruce trees. Foresters increasingly encountered various leaf spots, with the most notable being pine-leaf cast on pines and oak powdery mildew. Unfortunately, there is little hope for improvement, as ash dieback persists throughout the Czech Republic, primarily caused by a pathogenic ascomycete fungus.
While options for mitigating forest damage from abiotic factors are somewhat limited, the rapid advancement of modern technologies offers practical tools that could enhance and streamline forest protection measures against bark beetles and aid in the remediation of infected wood.
The afternoon session of this year’s Forest Protection Service seminar, titled “Harmful Factors in the Forests of the Czech Republic 2025/2026” (Škodliví činitelé v lesích Česka 2025/2026), took place on April 23 in Průhonice. Experts from both academic and commercial sectors presented methodologies for assessing the health of forest stands. This was achieved through data collection using remote sensing techniques and the potential involvement of artificial intelligence in analysis. Additionally, discussions included the development of new pheromone baits for the mass trapping of bark beetles. The seminar also highlighted the use of nanotechnologies in forest protection. More information can be found in the LOS 2026 Newsletter.
Assessment of forest stand health in the Czech Republic based on defoliation levels
Photo: European larch is part of our forests. Author: Jan Řezáč
To assess the health of forest stands, an annual visual evaluation of crown conditions, specifically defoliation (the loss of leaves, expressed as a percentage), is conducted within the network of areas monitored by ICP Forests at level I. Long-term data indicates that our forests are increasingly facing environmental stress, characterized by the combination of abiotic damage and subsequent biotic pest infestations, with varying sensitivity among different tree species.
In recent years, the average annual defoliation rates for our main tree species, apart from beech, peaked in 2019–2020. Since then, defoliation rates have shown stagnation or slight improvement, driven by several factors. Notably, the removal of the most damaged individuals from the evaluated populations, along with a genuine response of forest stands to more favourable precipitation years during 2020–2024, have contributed to this trend.
However, while total annual precipitation in the Czech Republic has not shown a clear trend, average annual temperatures are significantly rising. This increase raises the demands on plant transpiration, which impacts forest stands and leads to a worsening water deficit in the landscape, even during years with near-normal precipitation levels. Therefore, the current stabilization or reduction in defoliation should not be interpreted as the end of the crisis; our forests are still in a precarious situation. Extreme summer evaporation continues to weaken trees and hampers the replenishment of groundwater reserves, leaving our forests in a state of chronic threat.
Photo: Beech windfall – broadleaved tree species are not spared from damage. Author: Jan Řezáč
How can we enhance the resilience of forests to climate change?
To help forests cope with and adapt to changing climate conditions, genetic diversity is crucial for the stability of forest communities. This diversity enables forest stands to better withstand both abiotic (non-living environmental) and biotic (living organism-related) stressors. Therefore, in addition to maintaining species diversity in mixed forests, it is essential to preserve the genetic diversity of individual populations of our native tree species. These species have been under long-term pressure from natural conditions and have adapted over many generations. The successful and unsuccessful adaptations of these tree species are recorded in their gene pools, which scientists at the VÚLHM can study and analyse.
Considering the necessary transformation of the species composition in the forests of the Czech Republic, efforts are being made to preserve high-quality sources of reproductive material from forest tree species and to enhance the resilience of forests to ongoing climate change. Researchers are focusing on tree species that are currently underrepresented in forests, such as the wild service tree, small-leaved linden, large-leaved linden, sycamore maple, wild cherry, and thermophilic oak species. These species can significantly contribute to the overall diversity of forest ecosystems. Additionally, many of these tree species are important food sources for wildlife and are valued for their wood properties. Investigating the genetic diversity of these species is also a necessary step for their targeted use in forest management and for implementing preventive measures.
Photo: The species diversity of our forests also includes riparian stands along watercourses. Author: Jan Řezáč
To assess the genetic diversity of forest tree species and their ability to adapt to stress, scientists employ molecular methods, primarily through DNA and RNA analyses. One common technique is the use of nuclear microsatellite markers (SSR markers) in DNA analysis. These markers are known for their high reliability and reproducibility. They enable researchers to distinguish individual tree specimens (identifying clones), measure heterozygosity, differentiate between species or hybrids (such as large-leaved linden and small-leaved linden), and verify the origin of tree species in reproduction.
For more information, you may contact: RNDr. Petr Doležal, Ph.D., e-mail dolezal@vulhm.cz; Ing. Jan Lubojacký, Ph.D., e-mail: lubojacky@vulhm.cz; Mgr. Kateřina Neudertová Hellebrandová, Ph.D., e-mail: hellebrandova@vulhm.cz; Ing. Eva Pokorná, Ph.D., e-mail: pokorna@vulhm.cz.