In 2023, damage to forests by bark beetles has decreased again
The favourable course of weather conditions in recent years, in favourable concurrence with other factors, significantly dampened the ongoing gradation of bark beetles. For the third year in a row, foresters recorded a decrease in calamitous logging after the previous eight years of permanent increase.
Photo: Clearings following bark beetle logging, with typical “jagged horizons” on the slopes, Rožmitál Region, May 2023, VULHM archive
The bark beetle infestation has already affected almost the entire territory of the Czech Republic. Due to the large number of bark beetles still present in the forests and the unpredictable weather in the coming years, we cannot yet claim to have complete control over the bark beetle populations.
In comparison to the extremely unusual weather in 2015 and 2018, which had significantly lower than normal precipitation and much higher than normal temperatures, a significant change in the weather pattern occurred in the second third of 2020. Some sources even claim that the dry season in the latter half of the last decade had the most severe conditions in the last 500 years.
Photo: Four-armed „gallery“ of bark beetle Ips typographus, VULHM archive
In 2021, the weather conditions continued to develop favourably, with average temperatures and precipitation levels in line with long-term trends. In 2022, temperatures were above average, with a deviation of +0.9 °C, while precipitation was slightly below average at 93% of normal levels. In 2023, both temperatures and precipitation were above average, with a temperature deviation of +1.4 °C and precipitation at 107% of normal levels.
The data in the press release regarding the volume of wood or the area of stands affected by bark beetles are based on reports submitted by forest owners to the Forest Protection Service of FGMRI (VÚLHM, v. v. i.). These reports cover approximately two-thirds of the forest area in the Czech Republic. It’s important to note that when interpreting these figures in relation to the entire forest area, it should be taken into account that the data does not cover the entire forest area.
In 2023, approximately 3.42 million m3 of wood material was damaged by biotic harmful agents. This shows a significant decrease compared to previous years: 5.79 million m3 in 2022, 9.78 million m3 in 2021, 15.41 million m3 in 2020, 14.86 million m3 in 2019, and 8.59 million m3 in 2018.
Photo: Uninfested silver fir trees in a stand of bark beetle destroyed and dry Norway spruce stands, Sušice Region, July 2023, VULHM archive
The volume of incidental bark beetle logging in spruce stands decreased in 2023 for the third consecutive year, following eight years of continuous increase.
The widespread damage is primarily caused by the long-term overpopulation of bark beetles. The main culprit in the current bark beetle crisis is the spruce bark beetle. Other species, such as the glossy bark beetle and the northern bark beetle, typically infest the upper parts of the affected spruce trees.
The focus of the attack on spruce stands has shifted to southwestern and western Bohemia, while the unfavourable situation also persists in other areas, such as the Jeseníky Region, northern and north-eastern Bohemia, and the territory of the Bohemian-Moravian Highlands.
Last year, the colder weather in April and May was not ideal for the flight activity of bark beetles, similar to the year before. With the exception of August, the rest of the growing season had significantly below normal precipitation. The initially optimistic situation at the beginning of spring swarming gradually had negative effects, especially in July, when a three-month period of severe drought peaked. This led to the re-emergence of physiological weakening of spruce in most of the Czech Republic. Fortunately, the rainfall-rich final quarter of the year successfully made up for the moisture deficit in the soil.
Photo: Forest stand with dry Norway spruce trees, several years after being attacked by the spruce bark beetle. Location: Tábor Region, April 2024, VULHM archive
In 2023, the total volume of recorded spruce bark beetle wood was 3.201 million m3, showing a decrease of more than two-fifths compared to the previous year. The volume was 5.558 million m3 in 2022, 9.540 million m3 in 2021, and 14.894 million m3 in 2020.
If we recalculate the volume of spruce bark wood extracted in the past year to the total area of forests in the Czech Republic (reports cover 70% of the area), we arrive at a value of more than 4.5 million m3.
In almost the entire territory, the spruce bark beetles are causing a significant problem. The reported volume of bark wood represents an average of about 3.7 m3/ha of spruce stands of all ages in the Czech Republic, which is more than twenty times higher than the value of 0.20 m3/ha for bark beetle basic value allowed according to Decree of the Ministry of Agriculture No. 101/1996 Coll., as amended,
In 2023, the highest volumes of harvested spruce bark wood were reported in the following regions: Plzeň (700 thousand m3; 2022: 769 thousand m3), Olomouc (392 thousand m3; 2022: 420 thousand m3), and Vysočina (335 thousand m3; 2022: 976 thousand m3).
Additionally, more than 200 thousand m3 was recorded in the regions of Hradec Králové (241 thousand m3; 2022: 319 thousand m3), South Bohemia (238 thousand m3; 2022: 400 thousand m3), and Pardubice Region (213 thousand m3; 2022: 407 thousand m3).
Photo: Coloured changes of needles in the crown of Norway spruce tree infested by bark beetles, VULHM archive
With the exception of the north-eastern and western parts of the Czech Republic, there has been a notable year-on-year decrease in the spread of bark beetle infestation. Concurrently, there has been a significant decrease in the number of older spruce stands in hilly and upland areas across the entire territory of the Czech Republic.
In the western part of the state, where the calamity peaked later, it subsides with an appropriate time interval. The most problematic area was the territory of the Plzeň Region, which had the highest volumes of bark extraction. The situation has not changed significantly in the last three years in the Olomouc Region. In the Bohemian-Moravian Highlands, only a tenth of the extreme volumes that were reached at the height of the calamity in 2019 were recorded in 2020.
Processed according to data from the publication Forest Protection Bulletin, Supplementum 2024, which can be downloaded here.
Prepared by Ing. Jan Řezáč, VULHM, v. v. i., e-mail: rezac@vulhm.cz