Summary

The condition of forests in the Free State of Saxony has developed critically over the past years since 2018, leading partly to large-area disturbances. Since the weather pattern in 2021 was relatively favourable from an ecophysiological point of view, the crown condition of the forest trees was marked by temporary regeneration. After evaluating the data, it becomes obvious that the crown condition once again deteriorated in the current survey year 2022. Individual observation parameters did not just remain at a very high level, but hit new all-time highs. All in all, this process reflects the effects of the dry and warm weather since 2018. The marked precipitation deficit from March 2022 onwards caused the forest soil to dry out down to very deep soil layers in many sites during the subsequent vegetation period and compounded the forest trees‘ loss in vitality outlined above.

The entire hydrological year 2021-22 was marked by an unfavourable weather pattern. Temperatures were above the long-term average throughout almost the whole year. The winter months were very warm and the months from November to February only showed average amounts of precipitation. Furthermore, the spring period and the subsequent summer months were characterised by persistent drought. The soil water reservoir was thus progressively further depleted.

Apart from crown defoliation (leaf/needle loss) and the degree of yellowing, further characteristics such as blossom, fruit formation, number of needle age groups as well as biotic damage (caused by insects and fungi, etc.) and abiotic damage (caused by drought, fire and storm) were also recorded in the forest condition survey of 6,672 trees. The current average needle and leaf loss reached a new maximum of 27.0 percent within the 32-year monitoring time series. This is an increase of 1.9 percent compared to the previous year 2021 (25.1 percent). Consequently, the current value again clearly exceeds the long-term average value of 17.2 percent.

Each evaluated tree is classified in one of five damage classes based on needle/leaf loss in combination with any discolouration that may have occurred. The classification thus indicates a considerable impact on crown condition for 35 percent of forest trees (damage classes 2 to 4), a slight impact on crown condition for 43 percent (damage class 1) and no detectable impact on crown condition for 22 percent (damage class 0). This means that there is a shift towards trees with a marked loss in vitality.

The mean needle loss for common spruce is 30.0 percent, the highest value ever recorded, and 12 percent above the long-term average. Whereas high air pollution by sulphur was responsible for intense damage to the forests at the beginning of the 1990ies, persistent dryness, storms and biotic damage factors in the past years have led to a decrease in the stands‘ vitality in the majority of the Saxon forest areas.

Even though the decreasing infestation trend of spruce stands, largely caused by the eight-toothed bark beetle, which had been observable in state forests since 2020 and also in private and corporate forests as of 2021, continued in 2022, it still remained at an extremely high level. Hence the prognosis in terms of forest protection is still likely to be very critical in the short to medium run since it may be connected with both sharp declines in ecosystem services significant for landscapeecology, which have a long-term effect, and fundamental changes with regard to the regional availability of wood. The long periods of moderate to severe drought in combination with favourable conditions for harmful wood and bark-breeding insects had a particularly negative effect in the lower mountain ranges and hill country. Apart from forestry sanitary measures, the fact that spruce trees have already been lost on larger areas in these regions over the past years accounts for the decreasing infestation trend, even though the eight-toothed bark beetle‘s population density is still very high. By the end of September 2022, the amount of infested living trees recorded in the total forest area was approximately 511,000 cubic metres, corresponding to around 51 percent of the figure for the same period last year.

The needle loss in common pine decreased negligibly to 23.9 percent and is thus significantly above the long-term average for the overall time series (17.0 percent). Only 18 percent of the trees show no crown damage. 58 percent of pine were classified as slightly damaged and 24 percent as considerably damaged. Bark and metallic wood boring beetles once again caused an above average infestation in pine, affecting a total amount of 32,000 cubic metres, but a decreasing trend can be seen. The previous year‘s favourable weather conditions obviously continue to have an impact in this respect. Compared to 2021, around 24 percent of the amount of infested trees had been registered by the end of September 2022.

The current survey showed a slight decrease in the mean crown defoliation to a figure of 21.3 percent in the group of other conifers. This is the second highest share ever determined and a decrease of around 1.1 percent compared to the previous year.

The perennial bark beetle infestation, primarily in soft wood, has reached an intensity unknown since the beginning of regulated forestry in Saxony some 200 years ago. The reason is a very high share of spruce and pine stands that are in a phase in which they show a high to very high susceptibility to these species of insects. This can in no way be compared to either that of the forest condition before 1990 or to that during the mass propagation of the eight-toothed bark beetle in 1946/47. Many of the (sample) trees aged 60 years and older have been lost and died, mainly due to storms and pest infestation, since 2018. The figure was again 4.7 percent in the current year.

After last year‘s forest survey had determined a peak value of 36.3 percent for average defoliation in oak, the current survey showed an improvement to a value of 32.8 percent. However, 59 percent of oak are still classified as damaged, though this corresponds to an improvement of 7 percent. Infestation by wood and bark-breeding insects such as oak bark beetles and oak borers is at a high level in oak too. This development results from the weakening of mainly intermediate and overtopped (understory) oak due to the prolonged warm and dry weather.

The average crown defoliation in beech is now 20.7 percent and thus remains at the previous year‘s level. The share of trees classified as healthy increased slightly to 39 percent. All in all, the reaction to the dry periods in the years 2018-2022 was less severe in beech than in other species of trees. This result is probably not due to this species‘ higher resilience to drought but more likely to the structure of the sample grid, mainly covering beech stands of the medium mountain ranges that are less affected by drought. Similar to oak, beetle species that mainly colonize weakened beech, such as the small beech bark beetle, benefitted from the drought in the previous years.

The group of other deciduous trees is dominated by birch, which is much more common than oak and beech in the entire sample. Compared to the previous year, average defoliation increased by 1.9 percent to 26.6 percent. The share of undamaged trees remained at a level of 28 percent, whereas the slightly damaged other deciduous trees account for 37 percent. Compared to 2021, this is a drop of 6 percent. This percentage is reflected in an increase in the share of clearly damaged other deciduous trees to 35 percent. The level of damage due to ash dieback is still high in the Free State of Saxony, though only individual trees are affected. No die-off of ash has been found on larger areas so far.

In the past, high levels of pollution were caused by atmospheric deposition, especially in the higher regions of the Ore Mountains. Thanks to a clean-air policy and persistent efforts to remedy the severely acidified forest soils by protective liming, this impact could be reduced. High, above-average crown defoliation and/or discolouration were registered up until 1999 in this the most densely-wooded region of Saxony. The Ore Mountains have shown comparatively low needle and leaf loss of below 20 percent on average since the year 2000 for the aforementioned reasons. Due to the extreme weather conditions of the previous years and the renewed drought in the current year, the mean crown defoliation continued to increase compared to 2021 and has reached a new peak level of 25.8 percent.

The trend in the eastern regions, i.e. the Elbe Sandstone Mountains and Zittau Mountains, the Lusatian hill country and basin as well as the western Vogtland is opposite to this. The values in these regions were below the Saxon average at the beginning of the time series. But crown defoliation has increased here disproportionately since the extremely dry year 2003. After a significant rise in 2018, there was no recovery of the mean crown defoliation in these regions in 2019 and 2020. Whereas all three regions showed a more or less clear improvement in 2021, the values for the mean crown defoliation have risen again according to the current survey. A new peak value of 31.0 percent was determined for the Lusatian hill country and basin. The value for the regions of the Elbe Sandstone Mountains and Zittau Mountains rose to 35.1 percent, a new maximum of the overall time series. The value in the Vogtland is 23.0 percent, which is also the highest value ever determined in this region.