A Bark beetle is a hard-bodied insect, about the size of a grain of rice. He lives in forests and when the forests are healthy, the beetles are a nuisance, but just a part of the ecosystem. A healthy tree can produce resin or pitch and push the beetles out before too much damage is caused. A tree stressed by wind, drought or heat can’t fend off the attack and even a healthy tree can succumb if the beetles arrive in great numbers. Climate changes are related with the problem of invasive species, for example Ips duplicatus, which spread out to Slovakia at the end of the 20th century and became a competitor of indigenous species. In the picture below you can see Ips typographus, Ips amitinus and Pityogenes chalcographus which are indigenous species of bark-beetle.
There are extensive calamities caused by bark-beetle known in the world. In our natural forest there were no huge calamities. In recent past, especially few years ago, there was a big calamity caused by bark-beetle, though. Starting mechanism is usually increased amount of damaged trees caused by wind, drought, ice and so on. When the severe conditions persist, the further calamity occurs.
Forest coverage is cca. 40 % of the total area of the Slovak republic. The most common tree species is European beech (31 %), followed by Norway spruce (26 %), oak, pine and other tree species. Forests in Slovakia, more than in other Central European countries, has been for a long time intensively used primarily for the needs of agriculture and metallurgy, but later the activities of forestry in Slovakia contributed to reforestation of deforested areas.
As I have mentioned, one important factor influencing the forest is wind. Trees weakend by huge storm is more likely to be attacked by bark-beetle. There were major wind calamities in November 2002, November 2004 and August 2007. After windstorm in 2004 the bark beetle damages in coniferous forests rapidly increased and the current outbreak is the largest and most severe in recorded history.
Another important factor influencing incidental felling was a new law on nature protection that came into force in 2002. So all three major wind calamities mentioned above (from 2002 through 2007) were not processed completely due to a long administration process to get exceptions from large restrictions. As a result the cumulative bark beetle calamity has been rising till now. But also invasive species of plants, fungi and animals already cause economic and environmental damage to forests.
The bark beetle calamity arose not only in protected areas (national parks) but also in production forests. There were several reasons for this situation, such as insufficient network of forest roads and lack of money to process all calamity wood. State as well as non state owners processed only the wood they were able to sell immediately. If this was not possible, damaged or infested wood was left in the stands.
The most commonly used instrument in fighting against bark-beetle are pheromone traps. Pheromone traps are regularly controlled, in average once a week. By assessment of catched bark-beetle foresters use a scale where 2 cl is cca 800 beetles Ips typographus. For comparison it is 12 000 beetles of Pityogenes chalcographus.
Another way is felling one or a few trees to attract bark-beetles and then liquidation of these trees – when the infestation is smaller extent. If there are larvae, the tree will be treated by insecticides or it will be processed in wood-working industry. These measures are used usually from March to end of September.
Natural enemies of bark-beetle, for example Trichodes apiarius are also helping to its elimination. Situation nowaday is that many researchers started looking at the idea of fighting bark beetle infestations with one of the beetle’s own natural enemies, a fungus. Fungus-based insecticides had been developed for use on agricultural crops, but there was less commercial interest in treating forests. The return just wasn’t there for the big pesticide companies. This fungus kills bark beetles and has minimal or no effects on the other organisms. It acts like a predator.
In our forests it is important to switch our effort from preference of timber production to non-productive functions of forests such as soil and water protection, recreational function and so on. Moreover, it is essential that the public needs to be aware of forests importance and the need of professional, targeted and long-term management and support the creation of suitable legal and financial conditions.