In addition to bark beetles, forests are also damaged by wind and drought
In addition to biotic pests (beetles and fungi), forests are also damaged by abiotic influences, especially by wind and drought, which are closely related to the course of the weather during the year and especially to its extreme fluctuations. In 2022, compared to 2021, wind damage increased by 30% in forests and drought damage decreased by 14%.
Photo: Windbreak in forests damaged by bark beetle in Vysočina, FGMRI (VÚLHM) archive
Globally, the 2022 year was the sixth warmest year since 1880, when global temperatures have been tracked. The nine years with the highest global temperature thus fall between 2014 and 2022. In Great Britain, Ireland, France and Spain, the year 2022 was the warmest in the history of meteorological measurements.
In the Czech Republic, the year 2022 was the fifth warmest in history (since 1961). The average temperature reached 9.2 °C, which is 0.9 °C above the 1991–2020 normal. The beginning of the year, June and October, was especially warm. Precipitation-wise, 2022 was normal. Significantly lower than normal precipitation was recorded in March and October 2022.
All the following data on the wood volume or about the area of stands affected by abiotic factors represent sums from reports sent by forest owners to the Forest Protection Service, covering two thirds (66.8%) of the forest area in the Czech Republic. Therefore, it is not a recalculation for the entire territory of the Czech Republic.
According to the submitted records, the total volume of abiotic and biotic incidental logging reached 10.2 million m3, in 2022. In 2021, 13.8 million m3 was reported. In 2020, 19.8 million m3 was reported, and 19.2 million m3 of incidental logging was reported in 2019. Between 2020 and 2022, there was a decrease of almost 49%.
From the total reported volume of 10.2 million m3, there abiotic influences accounted for 43% (4.39 million m3), biotic influences for 57% (5.81 million m3). The volume of wood damaged by abiotic factors is comparable year-on-year (2022: 4.4 million m3; 2021: 4.1 million m3).
Abiotic causes of damage were dominated by wind in 2022, which, according to the submitted records, damaged 3.2 million m3 of wood. In 2021, the volume was about 30% lower (2.31 million m3).
In 2022, the proportion of wind damage to abiotic damage was 73%. In 2021, this share was just under 57%, and it was similar in previous years as well (2020: 61%, 2019: 58%).
Photo: Windbreak in forests damaged by bark beetle in Vysočina, FGMRI (VÚLHM) archive
The last three years (2020-2022) have been relatively favourable for the state of the forest in terms of alleviating drought stress. It is especially favourable when evaluated in relation to the previous dry to very dry period of 2015-2019. For full regeneration, forest stands would need more rainfall and, above all, more evenly distributed throughout the year. It was also favourable that the more significant dry periods took place outside the main part of the growing season – in March and autumn 2022
According to the submitted records, the volume of forest stands damaged by drought stress decreased in 2022 to 1,06 mil. m3, after 5 years of increasing of this kind of damages. Drought accounted for 24% of the total abiotic incidental logging, which is a significant decrease compared to 2021 – the share of drought was 38% in 2021, 35% in 2020.
Photo: Declining and dying oak stand, primarily damaged by drought, Křivoklátsko, author Jan Liška
According to the regions, the largest amount of incidental logging due to the action of all abiotic factors was reported from the Central Bohemian Region (674.2 thousand m3), in 2022. The second largest volume of this kind of logging was reported from the Vysočina Region (603.3 thousand m3) and the third from the South Bohemian Region (603.1 thousand m3). The Jihočeský and Vysočina regions appear among the first three regions for several years in a row, the situation in these regions is really unfavourable.
In case of wind, the highest logging volumes are reported for the year 2022 from the South Bohemian Region (approx. 566 thousand m3). The South Bohemian region dominates by wind damage for the third year in a row (2021: 474 thousand m3; 2020: 626 thousand m3; 2019: 371 thousand m3).
The volume of wood damaged by drought was the highest in the South Moravian Region in 2022 (approx. 242 thousand m3), where the situation was also unfavourable in 2021, when the volume of wood damaged by drought was approx. 353 thousand m3. However, there is a decrease, because in previous years drought damages reached over half a million m3 of wood and a considerable area of mature spruce and pine stands was harvested.
It is quite clear that the calamitous effect of the drought has moved from northern Moravia to southern Moravia in recent years, and from there the situation it is getting worse to the west, through the Highlands to central Bohemia.
Taking care about large areas of regenerated stands, which were harvested mainly in the last five years, became a challenging challenge for foresters.
You can find more information on the development of the forest health state in the Forest Protection Service Newsletter for 2023, which can be downloaded here.
Prepared by Ing. Jan Řezáč, FGMRI (VÚLHM, v. v. i.), e-mail: rezac@vulhm.cz, according to the text in the LOS 2023 Newsletter.