Changes in the Tatra forests. Not only spruces grow there anymore

Tatra forests change over the years. – For forest ecosystems, phenomena such as hurricanes, bark beetle outbreaks or fires have two sides of the coin. On the one hand, they cause destruction, but on the other hand, they give a chance for the growth of a new generation, which without such a “reset” would not have a chance to develop. This is what happens in the Tatra forests – said Professor Jerzy Szwagrzyk, head of the Department of Forest Biodiversity at the Agricultural University of Krakow.

As he recalled, in the previous century, Polish national parks were largely transformed by humans. This was also the case with Tatra Mountains, where spruce trees were planted and dominated the landscape. Over time, attempts were made to increase the share of other species, but progress was negligible. The change occurred only after the natural disturbances that hit the Tatra Mountains in the last two decades (mountain wind and outbreak of the spruce bark beetle). – A rapid reconstruction process is taking place right now. The Tatra forests are changing before our eyes. The new forest is completely different: in place of the spruce forest, a diverse mixed forest grows, full of, among other things rowan berries, sycamore trees, willow trees, beech trees – pointed out Professor Szwagrzyk. The regenerating forest in the Tatra Mountains is left to itself, which means that it regenerates automatically, without human intervention and control. One of the “obstacles” to this type of development of natural forests is the browsing (and eating) of young tree shoots by animals (especially deer and roe deer). However, as Professor Szwagrzyk explained, while in the case of commercial forests, fencing off young trees to protect them from animals is justified, in natural forests – not necessarily. – Of course, the growing population of deer poses a threat to the growth of small trees, but there is no such problem in the Tatra Mountains because the area affected by disturbances is so large that the animals are not able to eat everything – said the researcher.

And explaining all this – the mutual connections between violent phenomena, the process of natural forest regeneration and the browsing of young trees by deer – is the subject of the project “The impact of extensive intensive disturbances on the relationship between herbivores and natural forest regeneration” carried out by the professor’s team.

Research as part of the project is carried out in the above-mentioned Tatra National Park, as well as in the Roztocze National Park. In Roztocze, natural disturbances have recently been small and scattered, and the young generation of trees is not very numerous and is usually fenced off, similarly to commercial forests.

– We located and measured young shoots, their growth rate, the intensity of their cracking, the intensity of light at the ground and other aspects. The next step is to quantitatively analyze how many young trees of various species there are and how large the mass of shoots available to deer in the study area is, said the researcher. – Preliminary results of our research indicate that species commonly considered sensitive to herbivore pressure, such as sycamore or mountain ash, quickly reach a height that protects them from browsing under conditions of natural disturbances. With high availability of light in large areas, they effectively compete with shade-resistant species and constitute a significant part of the young generation of trees – he explained. He added that, as a result, the young forests emerging there are characterized by greater species diversity than older stands. – The results of our research may therefore constitute an argument for refraining from interfering with the natural processes of forest regeneration after disturbances – emphasized the expert. According to Szwagrzyk, in Poland natural forests constitute one percent of all forests, practically only national parks and reserves. – However, we are observing a trend to leave even some areas of commercial forests to natural processes. This is also what the European Union points out, among others, in its biodiversity strategy, he concluded.