Tree trap. Do you know what to imagine under this term? Every forester would explain to you that this is a felled and branched tree used to lure and catch beetles that harm trees by eating bark. This method of forest protection has been practiced for almost 200 years. We know which species of bark beetles can be traped, how traps are controlled, how they should be processed and much more. However, we still do not know everything.
A team of scientists from the Faculty of Forestry and Wood Sciences, CULS, in cooperation with colleagues from the Faculty of Forestry and Wood Technology of Mendel University in Brno, set out into the unexplored waters. They set out to increase our awareness of this method. They focused on specific factors that could affect the success of traps.
The study you are reading about took place during 2004-2007, in the period from December to April, in two different locations. In the first case, it was a forest near the town of Petřvald in the Moravian-Silesian Region. The trees here suffer from drought, infestation by the parasitic fungus Armillaria ostoyae (armillaria root rot) and the overpopulation of bark beetles that has been going on for 15 years. In the second locality, near the village of Psáře in the Central Bohemian Region, there are forests in relatively good health. Bark beetles reproduced here due to the drought in 2003. The specific species found in the localities were most often the spruce bark beetle (Ips typographus), the six-toothed spruce bark beetle (Pityogenes chalcographus) and the small spruce bark beetle (Ips amitinus).
And how did the scientists proceed in their experiment? A total of 295 traps were prepared. For this purpose, trees were selected from freshly formed forest edges with a trunk diameter in the range of 20-50 cm. By the end of May, the monitoring of the number of holes on the traps was always completed. Just to give you a clue: if you find more than one hole in one square decimetre, it is already a strong degree of infestation in the case of the spruce bark beetle. The monitored factors included daily temperatures, snow cover and the length of shading of the trap site. It is these factors that are crucial for the success of the studied method, as they affect the drying rate of the trap, and therefore its attractiveness for bark beetles.
According to the results, the mentioned factors had different impacts in the two study localities. Trees from the stands near Petřvald, felled more than 70 days before removal, had a slightly higher number of bark beetles. In the stands near Psáři, the significant influence of light showed. The traps, which were in the shade all day, were attacked by the bark beetle more than those exposed to the sun during the day. The sum of daily temperatures also affected the number of holes. Infestation with bark beetle was slightly higher at higher temperatures in the forests of Petřvald, while it decreased in the stands of Psáři. Snow cover proved to be a very important factor. Whether the trap was covered with snow during its use or lay in the snow, its bark beetle catching success was higher.
Based on this study, the researchers conclude that weather conditions from felling to tree trap removal have a major impact on the success of this method and that the choice of the optimal day for tree felling should not be based solely on calendar date calculations. The performed experiment confirmed our knowledge known from forestry practice and brought a new perspective on the operation of traps. So what are the recommendations and conclusions?
- Trees with a larger diameter and preferably trees in places without shading should be prepared as traps.
- Unfortunately, in stands that are highly stressed by the overgrowth of bark beetle and the occurrence of armillaria root rot, the factors of tree selection and preparation date do not affect the effectiveness of traps.
- If we know that a warm winter without snow awaits us, we should prepare the traps just before the flight of a new generation of bark beetle in the spring.
Due to the growing drought, we must take into account in the future that the bark beetle will not stop bothering us by attacking the trees. Therefore, it is necessary to know in detail the methods of their capture, so that we know how to increase the success of the fight against bark beetles.
Holuša, J., Hlásny, T., Modlinger, R., Lukášová, K., Kula, E. (2017). Felled trap trees as the traditional method for bark beetle control: Can the trapping performance be increased? Forest Ecology and Management. 404, 165-173.
prof. Ing. Jaroslav Holuša, Ph.D.
Professor Holuša is the head of the Department of Forest Protection and Entomology. From this position, he teaches forest protection and lead a research on a wide range of topics: from individual species of bark beetles, through pathogenic fungi, to abiotic harmful factors in forests, such as wind, snow or drought.