Hornets are “nature’s sanitation workers” who help oaks and create forest biodiversity

Verkių park, Punias šilas, Šimonių giria – these are just a few examples of protected areas where clear sanitary felling was started this autumn.

In order to stop the “harmful” population of the bark beetle typographer, which attacks fir trees, and to protect healthy trees, it was decided to cut down the fir trees that were damaged by this beetle.

However, the fellings caused many questions – not only dead fir trees were cut down in the protected areas, but also healthy trees – pines, oaks and other deciduous trees.

Spruce trees can defend themselves against bark beetles

According to Doctor of Natural Sciences Mindaugas Lapela, fluctuations in the number of species in nature is a normal phenomenon.

“Under conditions favorable to the beetle, such as dry and windy weather or poor farming, the abundance of the bark beetle typographer can increase very rapidly to large outbreaks within 1-2 years,” says the scientist.

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Mass drying of fir trees in Lithuania caused by typographers has happened several times in recent years: 1969-1973, 1974-1985, 1993-1997, 2001-2004.

According to entomologist dr. Eduardo Budrio, usually a spruce growing in good conditions, successfully defends itself against the typographer – it pours sap on the beetles trying to settle.

Photo by Žygimantos Gedvilas/BNS/Visit to the cuttings of the Labanor forest

However, spruces have a surface root system, so during summer droughts the sap pressure in the trunks becomes insufficient to defend against typographers.

It is especially difficult for firs to survive if they are planted in places with too low groundwater level for these conifers or too little peatiness and hygroscopicity of the soil. This is typical in reclaimed forests, where the water level is artificially lowered.

Climatic factors – summer droughts – damage the ecophysiological condition and immunity of trees, and it is biological factors, such as the bark-boring typographer, that physically cause death and implement changes in dominant species.

Photo by Irmantos Gelūnos/BNS/Autumn in the Labanor forest

Bark borer helps oaks to grow

Spruces in suitable habitats are highly competitive – their population suppresses seed regeneration of other tree species and can form pure spruce stands with relatively low biodiversity.

Therefore, in natural forests, typograph becomes a key species controlling the establishment of spruce trees.

This beetle acts as a “sanitary of nature” – it eliminates the weakest spruces, thus improving the gene pool of their population. Bark borers ensure that spruces grow only where the conditions are best for them, giving way to other tree species elsewhere. In this way, warbler breeding centers in the forest form a multi-species stand of various ages, thus ensuring the natural biological diversity of the forest ecosystem.

The mentioned facts are proved by the research conducted in the Białowieża Forest in Poland. In the mixed forest ecosystems typical of our latitudes, typograph has been found to be important for the natural regeneration of common oak populations.

The mentioned facts are proved by the research conducted in the Białowieża Forest in Poland. In the mixed forest ecosystems typical of our latitudes, typograph has been found to be important for the natural regeneration of common oak populations.

Young oaks are intolerant of fog and do not grow under the canopy of old oaks. However, under them, fir trees that are much more tolerant to fog grow successfully.

These are able to quickly stretch upwards, as the old oaks gradually die, fir trees dominate the tree. Then, in dry summers, the typographer spreads and kills some of the spruces in the fir trees that have formed.

When they collapse, glades are formed, suitable for the successful growth of light-loving oaks, which here are protected from deer scratching by lying fir branches.

The native firs fertilize the oak trees until they grow large enough to be deer resistant. Thus, the typographer ensures the regeneration of oaks in mixed forests.

Photo by Eriko Ovčarenko/BNS/Ažuolynas

Lack of dead wood is a danger to protected insects

According to M. Lapelė, the bark-boring typographer is one of the most important species of the coniferous forest ecosystem. The beetle creates habitats for thousands of other forest organisms, which are essential for a healthy forest.

By drying out the fir trees, the bark beetle creates habitats for one of the most abundant groups of insects, the wood-eating beetles.

A number of species of hymenoptera are also associated with rotting trees – wasps, ants, wasps and even two-winged – long-legged mosquitoes, flower flies, maggots.

Lukas Balandios / 15min photo/The life of ants up close

Also mushrooms, lichens, vertebrates – various species of woodpeckers, which feed on insects, their acorns, which later serve for other types of birds – owls, terns, starlings, acorns are also suitable for squirrels, dormouse, bats.

In Lithuania, even 80 percent. the survival of protected forest insect species is most threatened by the lack of dead wood. Many species of wood-decomposing fungi are also at risk. The other links of the forest ecosystem depend on these, enabling an unbroken chain of life that provides each other with food and a home.

Healthy spruces weaken, so cuttings have to be repeated

According to M. Lapelė, the situation of the bark beetle typographer reminded once again of the problems of forest management and preservation that have not been solved in Lithuania for decades.

“The current situation has clearly shown that the real battle is not with the beetle that causes the damage, but with the consequences caused by its activity. In order to preserve wood, European obligations are being forgotten, that felling in the forests of protected areas must not be used for growing wood, but for ensuring the good condition of protected species and habitats. Therefore, forest restoration should be directed to the challenges of climate change”, he says.

Until now, in Lithuania and around the world, sanitary felling is considered the main means of protecting forests from the bark beetle, but it is generally accepted that complex preventive measures are necessary.

“In most cases, whether you manage the hearth diligently or do not intervene at all, the final result in terms of the number of damaged trees can be similar. In this case, sanitary felling is an economic means of preserving wood as a raw material and income, and not a fight against the beetle.

Due to the released terpenes, the gaps, stumps, and cutting waste created during fellings become like a center of attraction for hornets. Spruce trees growing on the outskirts of new clearings become extremely vulnerable due to strongly changed microclimatic conditions and an increased number of typographers, as a result of which, in many cases, cuttings have to be repeated again and again”, says biologist Ainius Pivoras.

Typographer studies conducted in the countries of Central Europe and the Balkans have shown that its abundance in stands of natural origin, where dried firs are not removed, is approximately twice as low as in adjacent industrially planted spruces.

Photo by Irmantos Gelūnos/BNS/Autumn in the Labanor forest

This is because naturally grown spruces that have survived natural selection are more resistant, and they are additionally protected by various predatory insects and parasitoids, whose abundant populations develop by preying on various species of hornets that breed in dead spruce wood.

Meanwhile, in industrial forests, where dead wood is removed, there are few warblers and their natural enemies are even fewer, so their populations are not large enough and stable enough to control the mass breeding of typographers if the right conditions arise.

“Sengirės fondas” is a non-governmental organization that aims to preserve the old forests of Lithuania with all the life in them, to create long-lasting examples of sustainable nature, which are extremely important for the preservation of biodiversity and the reduction of the consequences of climate change – sengire, open for people to visit.

The foundation’s vision is Lithuania, where nature belongs to nature, it is allowed to form without human influence, where all organisms are equal and none is called a pest.

The fund was initiated after the successful premiere of the film “The Old Man” in Lithuania in 2018, which received great public interest, as well as national and international recognition. Half of the funds collected at the film screenings were allocated to the foundation’s activities.

Established in 2020 in January, “Sengirės fondas” today already takes care of more than 97.5 ha of forests – future sengirs. Thanks to the growing community of the foundation, the main activities – forest protection and public education – continue.