German forests vs. Bark Beetle

Like many other European forests, the German Forests are a vital part of the country’s cultural landscape and have a major role in climate leveling. Covering around 32% of Germany’s surface area, these forests are of extreme importance for nature and society.

Fig 1. Germany's surface cover by forests

As part of Germany’s ecosystems, German Forests comprehend many species of plants, animals, fungi and many other living beings that work together towards survival and their interaction keeps the forest alive.

Yet, one interaction is worrying the German society and its neighbor countries: the Bark Beetle – Spruce tree.

How can a small insect destroy large forests?

Fig 2. Adult Ips typographus (a) front and (b) side view. (c) Pupae in bark. (d) Damage on Norway spruce (Picea abies) at tree level (with one of several hundred galleries indicated with white arrows; MG = straight egg tunnel made by one mother and LG = winding larval tunnels), (e) Damage at landscape level of mixed forest with Norway spruce (all brown), while trees with green crowns are Scots pine (Pinus sylvestris) or deciduous trees.

In normal conditions, the European spruce bark beetle ( Ips typographus L.) are valuable contributors to the ecosystem balance as they help to manage forests and promote heterogeneous tree cover patterns that results in more tree biodiversity.

The adult beetles locate and enter suitable trees to lay eggs under the bark, the larvae feed and develop in phloem (vascular tissue of the plant that transports "foods" produced in the leaves to all other parts of the plant). Normally the beetle enter freshly dead or stressed trees by evading the diminished defense mechanisms.

Fig 3. Bark Beetle infested tree

In outbreaks, the beetles can exhaust the tree defenses through pheromone coordinated mass attacks, even in healthy trees, this way spreading throughout the forest.

Bark beetle outbreaks are also considered normal when triggered by storms that cause damaged trees resulting in an abnormal amount of timber for the beetles to colonize, this is necessary to decompose the dead trees.

What caused the beetle outbreak?

Climate changes created the perfect conditions for bark beetle population irruptions because:

- Warmer temperatures facilitate bark beetle survival and development (reduces winter mortality)

- Allows the beetle to spread to higher altitudes and latitudes

- Increases the probability of extreme weather events like droughts that reduces tree resistance, and storms that cause damaged trees

What is the impact on the environment?

Fig 4. Bark-beetle damaged forest in Germany

Nowadays the bark beetle is considered one of the most damaging pest insects of spruce forests in Europe and its consequences on the environment and society extend to:

- Loss of value of timber resulting in economic issues among forest related business

- Reduction of populations of endangered species

- Reducing the quality of recreational experience of visitors

- Compromising the provisioning of ecosystem services such as drinking water

- Spreading to new areas where trees had never contacted the beetle thus are defenseless.

- Increase of net carbon fluxes from land to atmosphere causing more climate change

The bark beetle outbreaks in German Forests and other European forests are a perfect example of the consequences of climate change and further problems that result from it, efforts are being taken by German government and European entities to control the damages but with low success.

References:

Hlásny, T., König, L., Krokene, P., Lindner, M., Montagné-Huck, C., Müller, J., Qin, H., Raffa, K. F., Schelhaas, M. J., Svoboda, M., Viiri, H., & Seidl, R. (2021). Bark Beetle Outbreaks in Europe: State of Knowledge and Ways Forward for Management. Current Forestry Reports, 7(3), 138–165. https://doi.org/10.1007/S40725-021-00142-X/TABLES/1

Holzwarth, S., Thonfeld, F., Abdullahi, S., Asam, S., Canova, E. D. P., Gessner, U., Huth, J., Kraus, T., Leutner, B., & Kuenzer, C. (2020). Earth Observation Based Monitoring of Forests in Germany: A Review. Remote Sensing 2020, Vol. 12, Page 3570, 12(21), 3570. https://doi.org/10.3390/RS12213570

Is the bark-beetle still here? - NordicWoodJournal. (n.d.). Retrieved April 25, 2023, from https://nordicwoodjournal.com/editorial/is-the-bark-beetle-still-here/

Powell, D., Groβe-Wilde, E., Krokene, P., Roy, A., Chakraborty, A., Löfstedt, C., Vogel, H., Andersson, M. N., & Schlyter, F. (2021). A highly-contiguous genome assembly of the Eurasian spruce bark beetle, Ips typographus, provides insight into a major forest pest. Communications Biology 2021 4:1, 4(1), 1–9. https://doi.org/10.1038/s42003-021-02602-3

Spruce bark beetle’s devastating impact on German forests | Forestry Journal. (n.d.). Retrieved April 25, 2023, from https://www.forestryjournal.co.uk/features/18766981.fighting-losing-battle/

Thonfeld, F., Gessner, U., Holzwarth, S., Kriese, J., da Ponte, E., Huth, J., & Kuenzer, C. (2022). A First Assessment of Canopy Cover Loss in Germany’s Forests after the 2018–2020 Drought Years. Remote Sensing, 14(3), 562. https://doi.org/10.3390/RS14030562/S1