ARE BARK BEETLES REALLY SO TERRIBLE?
The article by Heorhi Kazulka, Philosophy Doctor of Biology
The Belovezhskaya Pushcha
Published in «Byelarusskaya Lesnaya Gazeta» (The Byelorussian Forest Newspaper) Newspaper, #34 (439),
September 09, 2003
The spruce bark beetle is a serious vermin for the forest. It is a small beetle with a length of 4 to 5.5 mm. After substantial and numerous reproduction, beetles cause destruction of spruce forests over large areas. The bark beetle usually is a secondary vermin which first of all attacks weakened and depressed trees. However, when its number becomes too large, beetles are capable to attack quite healthy trees effectively, weakening them and ultimately dooming them to death. This is why bark beetles can bring great damage to spruce forests. This results in economic losses owing to necessary preliminary cutting of infected forest stands.
The biology of the bark beetle is specifically connected to its cycle development. After periods of the low number of beetle, picks of the mass breeding occur. It is during such picks that bark beetle causes damage to spruce forests.
It was noticed a long time ago that cycles of bark beetle are related to solar activity, which is characterized by cycles as well. The duration of a solar cycle lasts approximately eleven years. During this period the activity of energy processes on the Sun varies from a relative «rest» to a period of high activity, in which numerous solar storms break out. The strongest increase of the number of bark beetle populations is timed with periods of high solar activity. It must be noted that the dynamics of development of many other insect species — forest pests — follow the same principle. And insects are not the only ones, as many species of animals react to changes of solar activity. The activity of the Sun influences the productivity and the production of plants. The development of epidemics and the flow of many natural processes and phenomena are partially connected to solar cycles.
Picks of mass development of bark beetle occurred during the entire history of Belovezhskaya Pushcha. In 1882 — 1883 for example, bark beetle breaded very numerous after a powerful hurricane struck the forest. Man needed to clear cut an area of 1,550 hectares. A period of strong drought in 1919 — 1921 resulted also in mass breeding of the bark beetle population. In order to liquidate the vermin the English firm «Century European Corporation» felled damaged trees over two and a half years. In 1965 — 1967 spots infected by bark beetle spread out over an area of about 3,000 hectares and 178,000 cubic meters. It was a consequence of drought and recently executed drainage measures. Bark beetles centers occurred in 1986 — 1987. In 1994 — 1997 spruce trees died on an area of over 10,000 hectares with a total volume of 231,000 cubic meters. In 2001 a new cycle of mass breeding of bark beetle began following extremely adverse weather conditions over previous years. In that year 300 centers of infection appeared and over 100,000 cubic meters of spruce trees were infected over an area of 600 hectares. Drought during spring and summer 2002 aggravated the situation concerning the bark beetle even more.
We can see a peculiarity over the last decades, which is a more frequent appearance of picks of mass breeding of bark beetles. There are several reasons for this increase. Let us mention here drainage of wetlands, which was carried out both in the buffer zone and within the territory of Belovezhskaya Pushcha over the last fifteen to seventeen years. Because of that the hydrological situation has changed over a vast region. Acid rain, promoted by emission of sulfur and nitrogen to the atmosphere, promote weakening of spruces. Global warming influences the situation as well.
The spruce is situated at the southern border of its natural habitat in Belovezhskaya Pushcha. Therefore, this species is especially sensitive to the hydrological regime. Drainage resulted in decreasing a level of the underground waters by on average one meter in Belovezhskaya Pushcha. As a result the root system of spruces (especially when growing in heightened relief elements), formed in the period before drainage works were carried out, has been isolated from the capillary water border. Life conditions have become «unnatural» for spruce stands and spruces. Especially the old forest stands were not able to adapt themselves to these changed conditions. They weakened and finally broke up.
There is another reason which explains the vulnerability of spruce, which for some reason does not get much attention. However, it is an essential factor. From 1957 to 1991 Belovezhskaya Pushcha had the status of State Protected Game Ground (SPGG). One of its main tasks was to reach a bid number of wild ungulates for purposes of hunting by the party and state heads. As a result the number of basic hunting species of ungulates (red deer, wild boar and roe deer) exceeded the optimal level by three to five times during the eighties. It lead to complete annihilation of the undergrowth and the youngest generation of the pine, oak, maple, ash, linden and other trees in the central part of Belovezhskaya Pushcha. Spruce gained advantage of this situation, since this species is poorly consumed by wild ungulates. The spruce started mass intervention, even into stands of pine, which grown on dry sandy soils. Spruce is not a characteristic species on this type of soil in this region under untouched natural conditions. It resulted in formation of unstable stands of spruces, with violated structure and composition. Scientists started to speak about the problem of undesirable change of basic forest-forming species, first of all, of pine.
It is important to know that the State Protected Game Ground was a second intensive stage in the hunting economy. The first one dated from 1880 — 1910. At that time Belovezhskaya Puscha belonged to the Russian empire. It was property of the Romanov imperial family, which resided there during holidays. Belovezhskaya Pushcha by tradition was the hunting ground of people who ranked at the top of the state hierarchy. The Russian tsars have hunted in a great and rich manner. Resulting steady artificial feeding and well-organized protection the number of ungulates reached its maximum in 1904. In that year wildlife existed of 785 European bisons, 6800 red deer, 4966 roe deer, 2320 wild boar, about 800 fallow deer and 58 elks.
From that moment mechanisms of internal regulation of the populations lead to a decrease in the birth-rate of species. Numerous helminthological and epidemiological diseases broke out. Poaching had a big impact during the World War I. It resulted in a fast and complete annihilation of wild populations of European bison and Fallow deer. The last European bison was killed in 1919. Red deer and wild boar amounted to no more than 40 examples.
The results for Belovezhskaya Pushcha were catastrophic. Vrublevsky K.I., a member of the imperial commission, worked in the forest from 1907 to 1909. Describing this period in the history of Belovezhskaya Pushcha and characterizing the environment of the forest, he wrote: «Looking closely to the forest, we notice that it constitutes an organism today, which is deeply pathological, degenerated and dying out. The trees, which grow in the forest are divided into two layers precisely by a single horizontal line: the top layer is colored green by branches covered by leaves and the bottom is space where you can see deep in the forest. It consists just of trees and trunks. The line which divides these zones is located at the height of the muzzle of wild ungulates. If a branch is bent down into the bottom layer for any reason, it is immediately consumed by a »bit«.
Just as during the existence of the State Protected Game Ground, spruce also gained advantage in development and distribution compared to other forest-forming tree species.
If we look at the map of forest distribution in Belarus, it is clearly visible that Belovezhskaya Pushcha is an island for spruces at the southern edge of its natural distribution range. To the north, west and east such large areas of spruces are found in a radius of 150 to 200 kilometers.
An analysis of the age structure of spruce stands reveals that the average age of spruce forests in the Belovezhskaya Pushcha amounts to 112 years. Spruces in the age class of 30 to 60 years old completely dominate the second layer of pine, spruce and some other forests. According to data of studies carried out on permanent monitoring plots, the area of pine stands with a prevailing young spruce generation has increased to 22 percent since 1972.
Thus, in Belovezhskaya Puscha forest stands prevail in those age groups of spruce which were formed in periods of overpopulation of the Pushcha by wild ungulates (periods of reign of the Russian tsar and protection as State Protected Game Ground). These spruce forests grew up at untypical habitats, due to the absence of competition with other tree species. Their sustainability is low. These stands started to decay resulting land drainage and global warming by the time they reached the age of maturity. Today is simply the time of destruction of spruce forests which were formed during the period of reign of the last Russian tsars.
Some specialists state the opinion that Belovezhskaya Pushcha can lose spruce forests because of the activity of bark beetle. Such fears have no ground. First of all, bark beetle does not infect all spruces, but only weakened ones. Secondly, bark beetle is bound to a specific development cycle, just as, for instance, spruce itself. The sudden increase of the number of specimens in a population is later turned into a decrease and the whole cycle repeats. A decrease of the number of bark beetles is registered now. There is just one real difference: the life cycle of spruce takes 50 to 100 years, which is connected to its average life duration of 130 to 150 year under local environmental conditions. Scientific publications issued over the last 15 to 20 years devoted to forestry related problems of Belovezhskaya Pushcha «alarmed» the fact that spruce started to dominate the forest. In fact is has replaced pine from its traditional environment and a danger of changing forest habitats in the future comes up. And this is just why nature itself has taken care to restore the ecological balance of Belovezhskaya Pushcha.
There is another side to the «problem» of the bark beetle, which is not known to everyone. Scientific investigations have revealed that sites where bark beetle is present play an important role in conservation of biological diversity. As a matter of fact there is an ecological link between many species of plants and animals with bark beetle and with the use of dead wood of spruces as nutrition or as a habitat. Among these are many rare, threatened and protected species of plants, mushrooms and animals, for example, three toed woodpecker. Infestation by bark beetle stimulates the development of a highly varied mosaic of micro-environments with a specific microclimate. This adds to the increase of biodiversity of the concerned ecosystem. Disintegration of spruce forests after bark beetle infection leads to the appearance of open sites. This stimulates the growth of a young forest generation within the wood, it enriches the species composition of the forest and complicates (thus improves) layer and age structures. These changes render positive influences to the living grass cover, which suffers little amount of acting light under the canopy of spruces forest. The forest productivity increases, new species appear and flowering and seed production are intensified. After its decomposition dead wood enriches the soil with humus.
So, mass development of the bark beetle is a natural element of the dynamics of forest with a high share of spruce. Therefore bark beetle infestations do not threat the nature of Belovezhskaya Pushcha. In a primary relic forest environment like Belovezhskaya Pushcha bark beetles do not simply destroy spruce forests. They shape completely new forest ecosystems, allow multiplication of composition and structure of the forest and they save the unique biological diversity of the primeval forest.
According to the legislation the protection of this unique natural complex and preservation of its biodiversity must be priority in Belovezhskaya Pushcha National Park, as it is a Specially Protected Natural Territory. Therefore fellings of forests invested by bark beetle in the appropriate zones should be carried out in true consideration of these primary tasks. Fellings should under no circumstances be substituted to economic purposes.