The Pärnu River basin and floods

The Pärnu River has also been called the ‘Estonian Mississippi’, as it is the longest river in Estonia and like the true Missisipi is remarkable for its great floods. The basin of the Pärnu River represents an average cross section of more prevalent Estonian landscapes, as the river crosses different landscape areas from the Pandivere Upland through Central Estonian Plain and Soomaa on its way to the Bay of Pärnu. The basins of its bigger tributaries are located on the Sakala Upland. The Pärnu River gets larger only near the town of Türi, where larger tributaries of its upper reaches — the Rivers of Esna, Prandi and Vodja empty into it. From Särevere to the Vihtra rapids the river is lined with flood plain meadows, paludified in some locations.

The upper reaches of the Pärnu River and its tributaries flow through the region of the best farmland in Estonia — Järvamaa County. The landscape changes radically at the town of Paide. Starting from there the river basin includes large mire systems of Transitional Estonia (Kuresoo, Kikepera, Ördi, Pööravere, Tolkuse) and large forests, the best-known of which are the forests of Vändra, Kõnnu, Kilingi and Lähkma. In some locations, the landscapes of older times have been preserved, where farms and fields are situated on a narrow higher strip of land along the riverbanks, and mires and forests are located farther from the river. But the majority of these old farms have been abandoned, with only large old trees marking their locations.

Flood plain forests
Plant communities adapted to floods, such as flood plain grasslands, flood plain forests and swamp forests, disperse on the banks of the rivers. Flood plain forests grow on riverbanks that are flooded for shorter periods. In lower places farther off from the river, where the floodwaters remain for longer periods or where ground water is very near, swamp forests grow. The characteristics of the forest have been shaped by river floods, occurring every spring and, after great rainfalls, also in summer and autumn.

Flood plain forests have been preserved in only a few areas of Estonia, and very few of them have been preserved in the rest of Europe. These forests are rich in different plant species, the dominant species being black alder and grey alder, oak, elm, smooth-barked elm, and birch can be found there as well. The largest and best-known flood plain forests of Estonia grow in Soomaa on the banks of the Halliste and Raudna Rivers and in Kõrvemaa, on the banks of the Jänijõgi and Tarvasjõgi Rivers.

In swamp forests, black alder is widely spread due to the river floods and the fluctuating regime of ground water. In addition ash, aspen and smooth-barked elm grow there. The microrelief of flood plain forests is tussocky: water remains in hollows between hummocks even in summer. Typical swamp plants grow in hollows: Iris pseudacorus, Thelypteris palustris, Calamagrostis canescens, Scirpus sylvaticus, Galium palustre and the representatives of the genus Carex. Swamp forests can be found in Soomaa and on the lower reaches of the Pedja and Põltsamaa rivers (Alam-Pedja Nature Reserve).

Flood plain grasslands
The flood plain grasslands located along the riverbanks are the typical example of plant communities formed as a result of the joint influence of river floods and human activities. The growth of trees is hindered on flood plains, since floods bring suspension rich in nutrients, which remains on the meadows after the floodwaters recede. The area of grasslands and pastures was enlarged by cutting the flood plain forests. Empty flood plain grasslands are dotted by single larger trees and shrubs. The flood plain grasslands of Soomaa are characterised by large single oaks.

Currently, the majority of flood plain grasslands are overgrown with shrubs or even with forests, as a result of the cessation of hay-making. The vegetation of flood plain grasslands covered with shrubs has become poor. The protection of flood plain grasslands actually involves putting them to use. The more consistent the hay-making on the grasslands, the better preserved the characteristic abundance, and beauty of plant species. In recent years, former flood plain grasslands have been restored along the Halliste, Raudna and Lemmjõgi Rivers in Soomaa National Park.

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