Tomáš Vrška has been the Director of Mendel University’s forest since 2020. He previously worked as a researcher on the dynamics of forests and their applications in silviculture and forestry, “of course in the light of climate change”. The 10,500-hectare forest enterprise is owned by the university and was established 99 years ago, in 1923, for research and educational purposes. As a part of our series on environmental research at Mendel University, we interviewed Vrška on the future of the Czech forests and the adaptation of forestry to climate change. Photo credit: Coline Béguet / Brno Daily
What is the main role of the forest enterprise of Mendel University?
Our role is to support the research of students and academic staff at Mendel University and other universities and research institutes, with everything that is studied in the forest. This means basic research, for example soil sciences, ecosystems sciences, the ecophysiology of the trees, ecophysiology of the forest sites, dendrology, dendroecology and production ecology, which is a very important branch of science.
The main role is to find new methods, new approaches to silviculture, or generally new approaches to forestry based on research, based on the new outputs of science. In the current situation, with climate change coming faster and stronger, there are many scientific papers which present models for future changes of all the climate’s characteristics, such as temperature, rainfall, etc. We study these papers, we think about them, and we develop new silviculture models, new methods of how to work in the forest based on these scientific outputs. Here is the daily connection between the practice and the science.
So, for example, this is a question: how to change step-by-step the tree species composition of the forest? How to change the spatial structure of the forest? It generally means the transformation from even-aged forest models to uneven-aged forests. I can carry out, for example, a very fine thinning in a spruce forest and underplant beeches. Thinning means to select some trees to cut in order to lower the density and increase the quality, and we have many many kinds of thinning. And when the beeches have grown, I can do a second thinning, and so on. It is one of the ways to make the transformation.
What are even-aged and uneven-aged forests?
Even-aged models mean that trees are planted after a clear cut, often in lines, and grow at the same time. They are more or less the same trees from the point of view of height, volume and DBH. DBH means Diameter at Breast Height: the diameters of all trees across the world are measured at 1 metre 30, it means more or less the height of the human breast. This is simply because it is more practical to measure. Even-aged models are therefore unified in the structure and unified in the tree species composition. On one hectare, all trees are of the same species, have the same DBH and the same height.
Uneven-aged means there are many tree species which are mixed, and each tree is different from the one next to it. The mixture of trees from different species, planted at different times, also means trees with different heights and diameters.
And does that adapt better to climate change?
Yes! Of course!
And what makes the uneven-aged forests more adaptable to climate change?
They are more adaptable, or more resilient, because of the different tree species and their different resistances. One tree species is more resistant to the wider temperature variability for example, a second is more resistant to the rainfall variability, because every tree species has a different growing strategy, different roots system, etc. Foresters have to know how it is possible to mix tree species and which species it is possible to mix for the better resilience of forests for the future.
And why does it also help to have trees with different diameters?
If the trees have different parameters, they have a better fulfillment of the growing space. The growing space means the space from the soil surface up to the maximum height that trees can reach. In an even-aged forest the trees have small crowns because of the space. The uneven aged forest is made of trees which are different – different species, different structures – and they can better use this growing space. They can also better create the microclimate and they are more resistant to storms because the wind goes through these different tree structures and its power is not so concentrated. But the most important is the resistance to dry periods. Because during the summer, and this is the typical mark of climate change, there are long-term dry periods. If we have an even-aged forest of spruces for example, the spruces have a root system shape which is not so deep. So if there is a long-term dry period, they die, because the 30 centimetres where the roots are located are absolutely dry. In a forest with different trees, these trees have different root systems. Their root systems fill the soil at different depths, so there is a better distribution of the water between the trees, and this is a second reason for this resistance. The spatial structure above the surface and this spatial structure under the soil surface.
Czech spruce forests have been devastated during the last ten years by bark beetles, a natural parasite of spruces which became too numerous due to the dry and hot weather. Why will diversified forests also help to fight this problem?
Because here, in the even-aged forest, if one species of bark beetle comes, many of the trees die. This is a factor which affects all trees because they are all the same species. If the same bark beetle is in an uneven-aged forest, it can affect only some trees. Also, the next generation of bark beetles can’t find the same tree species in the surroundings, because there are different tree species. Trees of the same species are not planted next to each other and in between are other tree species which are not interesting for the bark beetles. So if the richness of tree species is higher, the probability of survival of the trees in this forest is higher too.
And does it also store more carbon?
That is a good question and it varies species by species. The carbon is mostly stored in the soil and secondly in the stem of the tree. From this point of view the question is definitely which tree species are in the mixture. But for carbon storage the more important thing is to have the forest cover in general. If the forest soil is functioning, if it is living, it stores the carbon. It means if you use this even-aged forest and if you bring the new generation using natural regeneration instead of planting on the clearcut, it is good for carbon storage too. It is not possible to say generally that one stores more carbon than the other.
What is the role of wood production in carbon storage?
The uneven-aged system can be intensive for wood production too; it is more resistant to climate change and it could be a very productive system for wood production. Wood is a very important renewable source of material. From this point of view it is very important to have stable forests. It can also be very important for the practical application of a circular economy, because it is a local product.
Even-aged, unified, forests are not good for the circular economy because here you have only one tree species, which has limited use. So not all the potential uses for trees needed in a region can be found in one tree species. If we talk about the circular economy, or now there is the model called the bio-circular economy, we need spruces for construction, but we also need for example beeches for furniture, we need poplar for boxes, etc. So, if you have very structured and species-rich forests, you can use them on a local scale, you can regenerate them naturally, it is positive for resistance to climate change, for support of the bio-circular economy and, of course, for stable carbon storage.
It is also necessary to say that wild, natural forests are carbon-neutral ecosystems. In natural forests, reserves, the trees are growing, dying and decomposing. This is a cycle. It is carbon neutral. Productive, exploited forests can be carbon positive, which means they can absorb more carbon than they release. On the condition that we produce high quality wood, which is used for table, bed, roofs, for long-term use. In this case, the carbon is stored for 100 years and it becomes carbon positive because in the meantime other trees grow in the forest and store more carbon.
On the other hand, if you use the lower quality wood for making logs for heating, or for paper, it is for short-term use. The carbon is going out into the atmosphere. So, from this point of view, it is very important for forestry to work responsibly, not to work with a short time rotation period for example. For us, it is very important to create diversified forests. And, of course, high quality groups which store the carbon.
And which tree species are recommended for planting in the Czech Republic?
It is first necessary to say that it is different in different regions. The vegetation here, in southern Moravia, which is a dry region, is very different to the vegetation in the mountains, the higher mountains, which are in our country 1,300 metres above sea level. And these tree species compositions recommended for the resistance to climate change of course change with the altitude. The survival chances of spruces for example decreases metre by metre with the altitude. Here for our dry and low elevation region, the key species are oaks, maples, ashes. Today, for example, it is more than 30 degrees Celsius, and there are more and more days, every year, with this temperature.
And I imagine diversified forests are also better for biodiversity, for animals?
Yes, it is a synergy. In even-aged, unified, forests, the space under the tree crown is unified, empty, with no vegetation and no grass because the sunlight cannot reach the soil. In diversified forests, because of the structure with different heights of trees, rays of light can find their way to the soil. Therefore, some vegetation can grow on it, which is of great help for the fauna. Also, different tree species mean different possibilities for the nests of birds, and different possibilities for invertebrates, because they need the direct radiation of the sun. Also, there are more and more possibilities for species which are strictly connected to the grass. And if we leave, somewhere, some pieces of the dead wood, for example from the trees which are damaged, or are partly decomposed because of some fungus, it is also better for biodiversity. To leave sometimes these pieces that are bad for the market is very positive for supporting biodiversity. So, from this point of view as well, it is absolutely better to have a diversified tree composition, for better, richer biodiversity.
