We continue a series of publications dedicated to the 75th anniversary of the Prioksko-Terrasny Zapovednik by a conversation with the candidate of biological sciences, Larisa Aksenova, the geobotanist.

On the left bank of the Oka River, opposite the city of Pushchino, on the ancient river terraces lies one of the main treasures of the Prioksko-Terrasny Nature Reserve – “Doly”. One and a half hundred years ago, in 1861, the Russian botanist Professor of Moscow State University Nikolai Nikolaevich Kaufman, doing floristic research in the Moscow province, made an amazing discovery. He discovered and described on the Oka terraces a tiny, but real plot of the typical Russian steppe. The phenomenon was called “Oka flora” and since 1866, “Doly” began to be protected as a unique natural object. The steppe island is very small – only about 36 hectares. But this is the northernmost steppe in Russia, completely isolated from its main range. Since 1945, the Oka Flora has been preserved by the Prioksko-Terrasny Nature Reserve.

About the phenomenon of “Oka Flora”, which attracts the constant attention of scientists – in an interview with a geobotanist, candidate of biological sciences, Larisa Aksenova.

Please tell us why the «Oka flora» is unique?

«Oka Flora» is a completely unique plant community. The uniqueness lies in the fact that just 100 km from Moscow, on the left bank of the Oka River, in a place called “Doly”, there are flood meadows with elements of steppe vegetation characteristic of more southern regions. Moreover, they are extremely rich in biodiversity. Here 172 plant species were recorded, more than 50 of which are species characteristic of the northern varieties of meadow steppes.
These are primarily cereals — Stipa pennata and Festuca valesiaca, Phleum phleoides. Two clover species Trifolium montanum, T. alpestre, Galium verum, green strawberries Fragaria viridis, Filipendula vulgaris, Potentilla arenaria and other steppe species are found here. Special rarities are Tulipa biebersteiniana, Scorzonera purpurea, Inula hirta. On the southern edge of pine forests grows steppe cherries (Cerasus fruticosa) – this is the extreme north of its range.

What are the versions of the origin of the «Oka Flora»?

Scientists have only hypotheses, among which there is even an anthropogenic factor. Along the Oka, in addition to «Doly», steppe slopes are still found in the Kaluga Region, and in the Moscow Region small islands have been preserved near Kolomna, Ozyory, and Serebryanoprudsky District. But such a rich and harmonious floristic complex in «Doly» is the only one. By the way, the feathery feather grass – a symbol of the Russian steppe – grows from these islands only here. There are studies that show that during the Holocene in the south of the Moscow region it was the steppe that dominated, not the forest.

But here is what is especially interesting – in «Dolу» there are plant species characteristic of southern Siberia and even the Far East. These are Draba sibirica, Carex obtusata, Melica picta and others. Most likely, this is preglacial flora. In this case, it’s not just a refugium of steppe vegetation, but a relic of some common ancient Eurasian Pleistocene flora, which miraculously survived.

How could he survive?

This, of course, is a happy coincidence. I must say that in this place the Oka has a strong bend and this bend on the left bank literally outlines this steppe island. On the south side of the river, on the north – the forest, creating a special microclimate. There was an interesting work of scientists from Pushchino on the temperature regime of «Dolу».
They found out: firstly, the daily variation in air temperature in the steppe communities during the growing season differs from other places; it is colder at night in «Dolу», and during the day, after the stage of temperature equalization, from 12 o’clock until dusk the temperature is higher than at other points. In the second half of the summer, «Doly» cools down more slowly and warms up faster. But it is especially interesting that the average daily temperature of the soil under the meadow-steppe communities during the growing season significantly exceeded the temperature of the soil under the mixed forest by about 9 degrees, and under the forest glades by 5 degrees.

Since these are meadow-steppe communities – there is a high evapotranspiration coefficient – that is, the evaporation mode provides a very favorable humidity regime. In combination with the temperature regime, this is a very special microclimate. There are studies that show that the solar radiation in “Dolу” is three times higher than usual for these places due to the southern exposure of the slopes of the terraces. In addition, the 2 lower floodplain terraces are flooded in floods, the river brings fertile silts and this combination of circumstances, this miraculously surviving biocenosis, supports.

Are there any special rarities in the Oka flora?

There are three species from the Red Book of Russia – these are Stipa pennata, Fritillaria ruthenica and Cotoneaster melanocarpa. Colleagues from Pushchino report that in PTZ there is only one bush of it – this is possibly the most northern cotoneaster in its natural range.

One of the special treasures of the Oka flora is the blooming Tulipa biebersteiniana with bright golden corollas. This is a very tiny population – only a few hundred plants and its number is still stable. Bieberstein tulips grow in several scattered groups on the border of the forest and floodplain. The state of these plants is constantly monitored by botanists from the reserve, as well as specialists from Moscow State University and from Pushchino. Bieberstein’s tulip has a property characteristic of bulbous ephemeroids – in one season they grow numerous, in another – they may not seem at all. Here microclimatic conditions did not suit them – and they did not seem, did not bloom. An outside observer may decide that they have disappeared, and they simply live underground and wait for favorable conditions. The next year, having increased biomass, they will please with their flowering, so botanists are closely following them.

What are the studies of the Oka flora?

Since the discovery of the Oka flora in “Dolу” floristic observations were constantly conducted. For 35 years, the study of the Oka Flora and the flora of the Prioksko-Terrasny Zapovednik in general was conducted by Professor of Moscow State University Pavel Smirnov. He was also interested in the relict origin of this steppe island. Systematic observations of the Dolу flora have been underway since the mid 70s of the 20th century. In 1975-1985, Vladimir Danilov, a remarkable biologist and local historian, was a senior researcher at the Prioksko-Terrasny State Nature Reserve; he was involved in the study of the Oka Flora associations. Now Nadezhda Zelenskaya, a botanist at the Institute of Fundamental Problems of Biology (Pushchino), is actively working with Oka Flora. All these observations are very important – because Oka Flora is such a breathing living community.

And what is the current climate change affecting the Oka Flora?

The last years of climate warming, of course, have an effect on the Oka Flora and, in general, on the flora of the reserve. As observations show, in the floodplain community there is an active increase in biomass. That is, according to the increase in biomass, the Oka floodplain enters into some new, not yet completely predictable period, so modern observations are especially important – some serious changes in the cenosis can be identified. From year to year, the ratio of species in the community may change – studies of recent years also show this.
A very warm, abnormally warm winter causes this year a very low groundwater level. Drought is possible in the spring. It is unclear how full the rivers will be, how the Oka River will flood. Changes in the water regime of the Oka in this place may cause some changes in the Oka flora.

And what needs to be done to preserve the uniqueness of «Dolу»?

Economic activity cannot be completely abolished there, otherwise overgrowth with shrubs may occur. In this case, ephemeroids, as well as feather grass, turn out to be the most vulnerable. There should be a moderate load. In this case, of course, it is very important to balance this load. Currently, the regime of keeping steppe communities in the reserve is annual haymaking. It should be carried out within strictly defined time frames for the proper maintenance of the life cycle of the steppe species populations, so that they all have time to leave the seeds. Experts give a variety of recommendations. Among them – the possible creation of agrarian steppe plots here – this method has already been tested in a number of territories and has led to a very good result – increased bio-productivity and preservation of floristic richness.

Many thanks!