KSU professor spoke about the first research results of the Great Meadow after the destruction of the Kakhovka HPP

After the destruction of the Kakhovka HPP dam by Russian occupiers on the night of June 6, 2023, the bottom of the former reservoir began to be rapidly overgrown with willow. Ukrainian conservation scientists are observing the changes occurring in this area, and their latest expedition took took place in May.

The results of this expedition and the first conclusions were shared with Ukrinform by a member of the board of the Ukrainian Conservation Group, Doctor of Biological Sciences, Professor of the Department of Botany at Kherson State University Ivan Moisiienko.

A SOUTHERN VARIANT OF THE FLOODPLAIN FOREST HAS FORMED

- Which expedition was this after the HPP destruction? Are there noticeable changes on the bottom of the former reservoir compared to previous surveys?

- After the Russian terrorist attack on the Kakhovka HPP, the ninth expedition has already taken place. It can be said that the changes are now not as noticeable as they were in the first year. Because when we arrived for the first time – three weeks after the tragedy – we saw a bare bottom, a sort of Martian landscape. But just four and a half months later, in autumn, there was a two-meter willow forest, and some trees reached three meters and eight centimeters. That is, it was a striking change. Now this forest is growing, developing, and becoming more complex.

- Explain, what does "becoming more complex" mean?

- There is a certain structure to the forest ecosystem. In the first two years, we couldn't even effectively call it a forest, because according to international definitions, thickets with trees up to five meters in height are not considered forests. And so, in 2025, the average height of the willow thickets was over five meters, and some willows were more than seven. That is, starting from 2025, we have the right to call the tree thickets on the bottom of the Kakhovka reservoir a forest.

Furthermore, forests are characterized by stratification. For instance, in the first year, these were simple thickets where both willow and herbaceous plants formed a single layer. But now, the stratification is clearly visible. There is a tree layer – significantly taller than the others, then a shrub layer, an herbaceous layer, and a moss-lichen layer. In the tree layer, willow dominates; in the shrub layer, tamarisk ramosissima.

The presence of a large amount of tamarisk is interesting. In fact, willow-poplar forests are intra-zonal, meaning they grow throughout Ukraine, near water, specifically rivers. They are also found, for example, in the Kyiv region, where I currently live, but these forests do not have tamarisk. There, other shrubs exist – grey willow or spindle, but tamarisk is a specific feature of southern willow-poplar forests. Therefore, I will note that a southern variant, rather than the forest type found in most of Ukraine, has formed on the bottom of the Kakhovka reservoir. One could even say that this brings it closer to Mediterranean-type forests.

I will also mention the high species richness. Along with the chief scientific officer of the Institute of Botany of the National Academy of Sciences of Ukraine, Anna Kuzemko, we made 47 descriptions. In some cases, the number of species reached almost 50. For such types of forests, these are very high indicators. Natural forests usually have about 20-30 species. This can partially be explained by the fact that the ecosystem is unstable; these forests are very young and, in addition to typical species – sedges, reeds – contain accidental elements, specifically weeds. As the forests develop, they will be displaced by typical native plants.

- In your social media posts, you mention the term “equilibrium forest.&rdquo Is this about trees growing in one period?

- Plant physiologists gave us this idea because experimental botanists accompanied us on the expedition. They say: if you are studying a forest, as a rule, there will be trees of different ages – from old to young. But here, all the trees are of the same age.

Scientists studying plant physiology worked in the expedition – Kateryna Romanenko and Oleksandr Polishchuk from the Institute of Botany. Their research helps unravel the mystery of such rapid growth of this forest. Because we say that the forest is growing at record rates, but we can only assume that rich soils, good water supply, and intense sunlight influence this process. But these are just our assumptions. And without physiologists, we cannot understand the mechanisms of why this happens.

Our colleagues recorded record levels of chlorophyll content in leaves and photosynthetic intensity in the forest on the bottom of the former reservoir. For example, the maximum coefficient of Photosystem II efficiency was 0.83. In ideal laboratory conditions, they achieved 0.78-0.8. But here, in the forest, we obtained a value of 0.83 – which is higher than in the lab and is the maximum possible. It is currently too early to make final conclusions. So far, certain interesting patterns have been established. Therefore, these studies will continue.

This interesting phenomenon is also related to the silt layers on which the willow grows. They are very rich in organic matter, where microorganisms are actively working, releasing a huge amount of carbon dioxide. This is the primary greenhouse gas, and if it all entered the atmosphere, it would be quite bad. But the willow intercepts a significant part of it. Colleagues recorded, for example, that the level of carbon dioxide in this forest at night is twice as high as during the day. This is because at night, the willow does not absorb carbon dioxide through photosynthesis. It turns out that the willow not only saves us from the spread of invasive species but also intercepts the carbon dioxide released during the life processes of the silt. This is very important. And on the other hand, this may explain such an abnormally high growth rate, because carbon dioxide is the primary element used to build the plant body.

WILLOW «PREVENTS» INVASIVE PLANT SPECIES

- If we are talking about zoology, what noticeable changes in the animal world did your colleagues record?

- As a botanist, I can say: if we take the first year, on the territory of the former reservoir bottom, we observed total dominance of plants that spread by wind. But as of last year, the proportion of those spread by animals has significantly increased. This is an indirect botanical indicator of increased animal activity. But a zoologist accompanied us on the expedition, the head of the board of the NGO «Ukrainian Conservation Group» (UNCG), Oleksiy Vasyluk. He noted small mammals and a large number of birds. We, the botanists, also saw many birds on the bottom of the reservoir – they are near any body of water. The birds are diverse; last year we encountered specifically sandpipers, and this year – red-listed marsh harriers.

I will also note that spiderwebs are now found in large quantities on the willows – just like in a real forest. You notice it because it catches your face, whereas in previous years, there were no spiderwebs. This is also an indication that there are more animals.

- Immediately after the destruction of the Kakhovka HPP, there were predictions that a mass spread of invasive plant species would be possible on the bottom of the former reservoir. In 2024, you said this scenario did not materialize. What about now? Are there invasive plants in this area?

- Invasive species are present, but in small quantities. The willow, as I already mentioned, «prevents» them by quickly forming dense thickets. Even near Maryanske (a village in the Kryvyi Rhi district of Dnipropetrovsk region, which directly borders the Kherson region, located on the shore of the former Kakhovka reservoir, – ed.) along the road, there is a succession of very aggressive invasive plant species. There, in large quantities, grow false indigo, pennsylvanian ash, and tree of heaven. But as you descend into the willow – they are not there, only isolated individuals. Although I understand that for false indigo, the conditions there are simply ideal – sufficient moisture, rich soils.

- Do we only have willow-poplar forest in this area?

- Willow-poplar forests are very characteristic of floodplains. However, oak, elm, and ash were much less widespread, on higher islands or on the supra-floodplain forest terrace. We have already noted ash and elm in the undergrowth of willow forests on the bottom of the reservoir, but so far, we have not been able to record any oak. In the Kakhovka reservoir, there were archipelagos of sandy islands – Velyki and Mali Kuchuhury closer to the left bank. I was once at Velyki Kuchuhury; there grew, for example, the Dnieper birch – this is our special subendemic species, included in the Red Book of Ukraine. I am sure that the birch is now spreading widely there because it is also a pioneer tree. The sands have been exposed and they should be overgrown with birch. But this area is closer to the left bank of the reservoir, and we cannot verify this right now, as you understand.

FOREST THAT GREW ON THE BOTTOM OF THE RESERVOIR, UNDER THE PROTECTION OF THE BERN CONVENTION

- Nowadays, many European countries talk about returning rivers to their natural regime. There, of course, this happens under different circumstances, but can we use the European experience in restoring ecosystems, or is there a reciprocal interest in your research?

- In the European Union, there are plans to restore the natural flow of rivers over 25,000 kilometers by 2030. This is a huge figure; it involves thousands of rivers where dams are being removed. But, as a rule, these are small rivers that cannot be compared to what is happening at the Kakhovka reservoir. That is, our experience is unique, although very tragic. Velykyi Luh is probably the largest willow-poplar forest in Europe. Therefore, foreign colleagues are very interested in the events in Ukraine.

Regarding our research, we have given presentations at universities in Canada, the USA, and European countries.

- In 2024, you said that the Kakhovka HPP should not be restored in the form it was. Has your opinion changed?

- I want to emphasize that the type of forest that has already formed on the bottom of the Kakhovka reservoir is included in Resolution No. 4 of the Bern Convention. This means it is protected throughout Europe, specifically in Ukraine as a signatory to this convention. Furthermore, we have managed to identify several plant species that are protected. For example, the creeping sedge is included in the Red Book of Ukraine, as is the previously mentioned Dnieper birch. There are significantly more animal species here that are subject to protection. That is, this forest is gradually acquiring increasing conservation value. In my opinion, the best option is to create a nature conservation site here. We say that this forest is no longer just a natural but also an important cultural heritage. Because six out of ten Sichs were within the boundaries of Velykyi Luh; this is effectively the cradle of the Ukrainian Cossack state. Therefore, the idea has arisen to declare this historical and natural monument as a UNESCO mixed heritage site.

According to Ukrinform