Damaged timber due to natural hazards

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Background information

Logging in the forest is not allowed without a permit. For this reason, the trees to be felled are selected according to forest ecological and forest economic criteria. A permit is required for all felling in municipal, agricultural, sheltered and protected forests. Snow pressure, dry periods (drought), storms (windthrow), forest fires and pest infestations damage trees and require a permit for felling.

Extreme weather and climate events are expected to change in frequency and intensity as a result of climate change (1). In addition to the acute natural hazards (disasters) caused by climate change, the lack of silvicultural adaptation measures will lead to an increase in damaged timber.

Description of the results

The increase in weather and climate-related damage to timber is not yet a statistically significant trend. In recent years, the occurrence of damaged timber has been strongly influenced by major weather-related events. These events are reflected in the statistics of the following year‘s Wood Report.

Storms of the previous year are clearly visible in the data of the individual years. In 2000 (storm Lothar in 1999) and 2003 (a stronger storm from northern Italy in 2002) extreme weather events caused particular damage in the forest stations Welschnofen/Nova Levante, Brixen/Bressanone, Mühlbach/Rio di Pusteria, Welsberg/Monguelfo-Tesido, Deutschnofen/Nova Ponente and Kaltenbrunn/Fonane Fredde (2). After the storm Vaia and the windthrow in 2018, the amount of windthrown timber increased noteably in the following years of 2019 and 2020. In South Tyrol, 5,918 hectares of forest were affected, representing 1.7% of the total forest area. The amount of damaged timber corresponds to almost three times the annual felling rate (3). After the snow pressure events, a large amount of damaged wood remained in the forest. The bark beetle outbreak started in 2020, where it first affected the wood on the ground. From June 2021, spruce bark beetles multiplied rapidly due to a heat wave and there was a noticeable infestation of standing timber. In 2022, the bark beetles had a high reproduction rate due to a spring with low precipitation and a particularly dry and hot summer (4). In 2022, 83% of the timber was harvested according to weather-related criteria.

Snow pressure occurs relatively irregularly in the data sets. The amount of snow pressure damage is difficult to determine because the damage is very localized and only small amounts occur in decentralized areas. In steep and impassable terrain, these damaged areas are not worked. The logs are left lying around, providing an entry point for insect pests, especially the spruce bark beetle. November 2019 was particularly affected by snow pressure, when three low-pressure systems from the Mediterranean over South Tyrol caused a lot of precipitation, mainly in the form of snow (about 1.5 meters). This resulted in 900,000 cubic meters of damaged timber, equivalent to 1.4 times the annual felling rate for South Tyrol. The forest inspectorates of Welsberg, Bruneck and Brixen were particularly affected (3). The lack of thinning to maintain and stabilize the forests favored the extent of the damage caused by the snow pressure events. The close proximity of Vaia and the snow pressure events aggravated the wood crisis in the forest.

Drought weakens trees and can lead to damage such as dry rot. Drought-stressed trees are weakened trees that suffer from lack of water after periods of heat. They have small, translucent or partially wilted or missing leaves. The lack of rainfall also increases the risk of forest fires and biotic damage caused by pathogens. Windthrow and snow pressure damage also provide ideal breeding grounds for insect pests, especially the bark beetle. It can therefore be assumed that the proportion of biotic damage will increase significantly in the future compared to the low level of damage recorded in the data to date.

Other environmental stressors, such as air pollution, weaken tree populations and make them more susceptible to insect pests and fungal diseases, especially if the stress persists over time (5). To maintain forest resilience, it is essential that forests are managed in a way that is appropriate to their location. It is therefore important to promote semi-natural forest stands, consisting of variably-aged, vertically and horizontally well structured mixed stands of site-appropriate tree species, as close as possible to the potential natural vegetation. Secondary coniferous forests, developed for economic reasons as poorly structured, similarly-aged coniferous stands, often not adapted to the site, are generally the most endangered stands.

Global warming increases the carbon input into forest soils by accelerating the growth and turnover of fine roots. This would be positive and mitigate or partially compensate for the process, as the carbon loss from the soil could be partially offset or cushioned by increased microbial respiration. However, as forest soil temperatures rise, there is an increased risk that the forest will lose its function as a carbon sink and become a carbon source (6).

Method

The forestry law in Italy is a soil protection law (DECRETO LEGISLATIVO 3 Aprile 2018, N. 34). This means that all forests in Italy are protected forests. In order to be able to harvest or fell trees, the trees must be authorized for harvesting by means of a local inspection, by marking them and documenting this in the harvesting report. The advantage of this is that the trees to be harvested are professionally selected according to silvicultural and forest ecological criteria.

The timber report shows the year in which the timber was processed, not the year in which the damage occurred. It is recorded in solid cubic meters of timber, a report is completed and then entered into a computer system to compile forestry statistics.

Sectors affected

• Forestry

• Settlement

• Traffic infrastructure

Comparison to Austria

Damaged timber due to windthrow, snow pressure, avalanches and debris flows is noticeably increasing in Tyrol, Austria (Amount of damaged timber in Tyrolean forests, 2003 to 2020). The years 2012 and 2019 stand out for the amount of timber damaged by snow pressure, while the years 2015 and 2018 stand out for windthrow. Throughout Austria there is an increase in the amount of damaged wood due to biotic damage (especially bark beetles), storms (windthrow) and snow pressure (7). The amount of damaged wood due to windthrow was particularly high in 2007 and 2008 due to several major storm events. As a result, the use of beetle-damaged wood increased accordingly.

Related indicators

Further research at Eurac Research

The future of forests

References

1.     European Environmental Agency. 2017: Trends and projections in Europe 2017Tracking progress towards Europe's climate and energy targets.- EEA ReportNo 17

2.     Autonome Provinz Bozen – Südtirol, 2004: Agrar- und Forstbericht 2003. Ressort Landwirtschaft, Forstwirtschaft, Tourismus und Bevölkerungsschutz

3.     Autonome Provinz Bozen – Südtirol, 2020: Agrar- und Forstbericht 2019. Ressort Landwirtschaft, Forstwirtschaft, Tourismus und Bevölkerungsschutz.

4. Autonome Provinz Bozen – Südtirol, 2022: Agrar- und Forstbericht 2022. Ressort Landwirtschaft, Forstwirtschaft, Tourismus und Bevölkerungsschutz.

5.     Zebisch M., Vaccaro R., Niedrist G., Schneiderbauer S., Streifeneder T., Weiß M. L., Troi A., Renner K., Pedoth L., Baumgartner B., Bergonzi V., 2018: Klimareport – Südtirol 2018, Bozen, Italien: Eurac Research

6. Reichstein, M., Bahn, M., Ciais, P. et al., 2013: Climate extremes and the carbon cycle. Nature 500, 287–295. https://doi.org/10.1038/nature12350

7.     Ebner, G., 2020: Schadholzbilanz in Mitteleuropa (Trends, Folgen für Waldbesitzer und Abnehmer).- „Holzmärkte im Umbruch“, Forstökonomische Tagung 2020/Webinar.

Contact

Eurac Research: Christian Hoffmann, Institute for Regional Development

Data provided by: Amt für Forstplanung of the Autonomous Province of Bolzano