árka Valley
árka Valley
The árka Valley denominates the part of the Litovice (here already árka) Brook between the Dbán swimming pool and the Vltava, deeply and sharply cut into solid Proterozoic rocks. The árka region includes also the open valley of the tributary from the airport, the valley of the Nebuice creek and the brook coming from Housle near Lysolaje. The area is characterized by relatively great differences of elevation from 180 m at the brook inlet into the Vltava to 364 m above sea level on the top of the Kozák Rock and the abák which soar above the surrounding plateau as knobs. The whole area is included in the árka natural monument and its most valuable parts have been declared small protected areas.
árka Valley
The árka Valley is the best preserved natural region northwest of Prague, which is due to its diversely articulated ground relief on resistant rocks appearing in numerous outcrops. Thanks to this also relatively large forest areas have been preserved, recently extended by tree planting, as well as xerothermal rocks and slopes. Also extensive wet meadows in the fluvial plain are significant. The area includes also the sites of important primeval settlements and pilgrimage places of later date, such as St. Mathews. Its popularity increased also by the Smetanas symphonic poem of the same name forming part of the symphonic cycle My Country, as well as the former National Theatre stage below the Dívčí Skok (Girls Jump).
In the framework of Prague árka provides a magnificent section of the Kralupy-Zbraslav group of the Barrandian Proterozoic characterized here by extraordinary representation of silicites - lydites cropping out in the form of wildly cleft rock masses and forming the unique gorge of Dbán, the entrance gate to the árka Valley. Also Proterozoic shales and greywackes crop out in many places being overlain by almost horizontally bedden Cretaceous formations along the upper edge - Cenomanian sandstones covered by sandy marlites, best uncovered in the broader environs of Nebuice. Also the lower Ordovician formations crop out near the Dbán swimming pool and in the right-hand valley slope near Jenerálka. The Quaternary is represented by thick loess drifts, once exploited for brick manufacture, and boulder screes below lydite rocks. Near the Čertův Mlýn (Devils Mill) the right-hand slope is covered with open boulder scree, the only one in Prague territory. Also the fluvial plain sediments are well developed, interspersed locally with limestone incrustations. Remarkable is also the Housle clough cut in loesses, sandy marlites and sandstones underlain by proterozoic shaks affected by tropical weathering.
The area, situated in the margin of a the chernozem region, is characterized by the prevalence of brown soils of different nutrition value and rankers on rock outcrops and sheer slopes. On loesses there are typical brown earths in the valley and chernozems along the northern margin in the lower part.
The whole árka area forms part of the ancient settlement region where man has influenced vegetation development for seven thousand years. That is why the whole area has been covered with a mosaic of forests, bushes and open areas of different kind since time immemorial. With the exception of rocky steppes on inaccessible sites all surfaces have been influenced by the activities of man - herdsman, user of wood and farmer.
Initial woods were of xerothermal character and comprized oak and hornbeam woods, acid, partly dwarfed oak woods with relatively small areas of scree woods and fluvial plains. On sheer slopes facing the north also beeches could be found. Only very little has been preserved from these original woods, the biggest remainder being the Nebuice Grove. Untill last century the area had a prevalence of pastures and extensive orchards with varying quota of xerothermal elements. Important part was played by rocky steppes and thermophilous heaths on top of lydites. An entirely specific formation consists in the rocky steppes of the Dbán gorge the diversity of species and structure of which is due to its enrichment by primeval hillforts erected on these rocks.
At present the forest cover of the area is relatively large thanks to the trees planted at the end of last century with the prevalence of alien wood species, such as false acacia, austrian pine, red oak as well as spruce - an entirely unsuitable species for this dry area. In the course of the past decade the area is becoming spontaneously overgrown with trees and bushes, at present forming a continuous cover of surfaces entirely bare as late as the Second World War. Also some invasion elements have penetrated here such as touch-me-not (Impatiens glandulifera) in the Dbán. This development has resulted in considerable empoverishment of the initial floral wealth of the árka Valley.
The vertebrate fauna comprises the species occurring in the whole Prague area, although some animals which had not lived here for a long time, such as the wild boar, seem to be returning here. Woods and bushes provide ample nesting opportunity for a number of birds. Important are also minor insects and other invertebrates on rocky slopes and rocks as well as in moist valley meadows to bogs. Until recently some species, known in the environs of Prague only from this area, have been living here, such as the minor spring snail (Bythinella austriaca) on Jenerálka and in the Nebuice Creek.
The original woods, managed mostly as sprout woods were affected significantly by various interference, such as pasturing and litter raking, as a result of which they have lost the major part of their herb layer. At present newly planted woods prevail the composition of which differs considerably from original woods. They are managed as special-purpose suburban woods and are desolate in the parts of difficult access. The herb layer often is of ruderal character.
The árka area has been settled continuously since primeval times. Middle Paleolithic men dwelt along the Vltava and a younger Paleolithic settlement was ascertained e.g. in the brickworks on the Jenerálka. Since the Neolithic settlements of farming and pasturing types were continous. Important buildings dating from that time are the hillforts on the esták and Kozák Rocks as well as the Slavonic hillfort in the árka Valley of a later date, which covered a considerable area. In the lower part of the valley, the so-called Upper and Lower árka, as well as Lysolaje, the buildings form a continuous chain at present. Higher up in the valley there is a chain of flour mills (e.g. Devils Mill) and farms, such as elivka or Vizerka. Below the Dívčí Skok (Girls Jump) a small swimming pool was built, above the valley entrance the Dbán dam with a reservoir and recreation facilities. Continuous urban construction has approached the valley from the south. There are no major industrial enterprises in the árka Valley or its adjacent valleys. Minor brickworks (Jenerálka, Dubový Mlýn) exploited loess drifts. Otherwise the area was influenced by adjacent communities.
In the past fruit orchards flourished here and the meadows were mown regularly. At present these activities have stopped mostly. The wide árka Brook is polluted considerably, as in its upstream part it flows through extensive neighbourhood units and intensively exploited agricultural areas. The pollution is contributed to also by the nearby airport. árka has become an important suburban recreation area in which some activities, particularly mountaineering, exceed the limits of its capacity. At present it is covered by a network of small protected areas in árka protecting the most valuable areas, primarily the rocky steppes and xerothermal slopes. Of no smaller value is its geomorphology including the instructive exposures of Proterozoic rocks. Although its living nature has suffered considerable losses, árka still is a rich and remarkable area requiring special nature protection.
In the past the árka Brook eroded a remarkable canyon and has preserved its strong and wild flow until the present.
The central part of the árka Valley near the Vizerka natural monument (PP).
The lydites have formed interesting shapes in the árka Valley.