In accordance with different climate a borderline was defined in the southern part of Prague between the phytogenetic regions of the Bohemian thermophyticum and the Bohemian-Moravian mezophyticum. In the framework of the Bohemian thermophyticum Prague area lies within the range of the following phytogeographic districts: Central Bohemian Tableau, Bohemian Karst, Lower Vltava Valley, Prague Plateau and slightly also Central Labe Basin. Bohemian-Moravian mezophyticum is represented by the district of Middle Vltava Valley and, in the direction of Libuš and Točná, the Říčany Plateau separated from the Prague Plateau by the line proceeding from Libuš to Krč via Chodov, Háje, Pitkovice, Koloděje, Běchovice and on to Klánovice (see p. 17).

Phytogeographic map of Prague (Centennial Prague XV, 1985, adapted).

Finally mention should be made also of the significance of the river phenomenon of the Vltava and its left-bank and right-bank tributaries for the flora and vegetation of Prague. The deep incision of the watercourses into the Tertiary plateau in the course of the Quaternary has produced the present ground relief in which the initial flat landscape is furrowed with the deep Vltava valley in the south-north direction and with euqally deep brook canyons in the west-east or east-west directions. The local difference of elevations is dramatic, often exceeding 100 m; we could almost speak about "submerged mountains".

Influence of slope orientation and inclination on solar energy input in kcal/sq.cm. It follows that the 5-30^o slope oriented to SW, S and SE is warmest in summer and the 60-80^o slope oriented to the South in winter.

The various directions of the main and the lateral valleys gave rise to the most varied slope orientations to the four cardinal points, the most varied angles and with a microrelief of small terraces and ridges corresponding with the weathering character of various rocks (limestones, shales, sandstones, lydites, quartzites, etc.). The slope orientation and angle are of principal significance for solar energy input in the course of the year, and particularly during the vegetation period (see p. 16). Solar energy is directly connected with the temperature regime in the soil and on plant surface which influences soil and vegetation evaporation. The sum of these ecological conditions has a long-term selective effect on plants and animals and generates specialized communities on sites of different types. At present, when Prague is a big city with all negative characteristics of this settlement type, the river phenomenon is the principal reason why the flora and vegetation of Prague are so rich: the steep slopes are natural inaccessible refugia for the elements of nature.
What outstanding elements can be found in Prague flora at present? The most important are undoubtedly the rock species and the species of xerothermal forestfree regions, typical of the thermophyticum. However, it is not a uniform group, each species having a different territory, development centre, glacial refugia and routes of postglacial migration. Therefore we can divide them only generally into several groups, such as the continental species with old migration period dating to the end of Pleistocene and beginning of Holocene. This group includes e.g. the walis fescue (Festuca valesiaca), steppe sedge (Carex humilis), sand cinquefoil (Potentilla arenaria), foetid meadow-rue (Thalictrum foetidum).
The most numerous group comprises the submediterranean species the probable refugia of which were in the western or eastern Mediterranean. Their propagation direction and their probable glacial refugium can be estimated on the basis of their present area. For instance the eastern boundary of the western - mediterranean - area of the hedge lily (Anthericum liliago) is in the very Prague region, in the Vltava valley, beyond which it can be found on a few solitary sites along the Labe (Elbe). On the other hand, the probable glacial refugium of Anthericum ramosum was probably near the Black Sea from where it propagated westwards, reaching as far as Western Europe.
Also the group of the character of Central European endemites has a great number of representatives, including e.g. Seseli osseum), the hedge-mustard (Erysimum trepidifolium) the Bohemian iris (Iris bohemica), the Bohemian meadow anemone (Pulsatilla pratensis bohemica), the bellflower (Campanula gentilis), the rock violet (Viola saxatilis), the blue mountain grass (Sesleria albicans), the milk trefoil (Chamaecytisus ratisbonensis), and others (see the map of occurence of some typical geoelements).

Section of the Tiché Údolí (Quiet Valley) near Spálený Mlýn with cryophilous heaths on northern slope and thermophilous rock communities on southern slope and a conserved fluvial plain on valley floor.

Section of the Džbán gorge in the Wild Šárka shows vegetation differences on rock faces of different orientation.

Until recently Prague has abounded in the flora of natural substitute sites - river bank, aquatic, meadow, wetland and fen flora. This flora was most heavily affected both by the change of the agricultural regime in marginal city parts and by the progress of construction and the planting of artificial woods, intended to provide recreation for the new city population. The previously numerous species of orchidaceous plants, among which Čelakovský (1870) mentioned the lesser butterfly orchid (Platanthera bifolia) and the green-winged orchid (Orchis morio) as most frequent, have practically disappeared from Prague, similarly as the gentians, gentianellas, the superb pink (Dianthus superbus), the globe flower (Trollius europaeus) and many others.
In the north of Prague the Central European forest flora is almost absent or occurs in minor fragments - a fact connected with very old settlement of this areas with rich loess soil lasting since the very Eneolithic. In the south of Prague with stony soils of poorer quality and colder climate some natural forest complexes have remained surprizingly well preserved, having never been entirely felled and converted into fields or coniferous monocultures (e.g. Radotín Valley, Břežany Valley, Komořany Woods, Chuchle Grove, Vidrholec) which enabled also the preservation of the natural forest flora species.
As Prague has numerous fragments of natural vegetation it was possible to compile a reconstruction map of its whole area (Moravec, Neuhäusl, et al. 1991). With regard to the relatively high diversity of bedrock, ground relief and climate it was possible to give the map a relatively small scale of 1 : 25 000 which has made it possible to differentiate 18 mapping units: the boggy alder woods (Alnion glutinosae) in wet ground depressions, anmoor soil type, the stitchwort-alder wood (Stellario-Alnetum glutinosae) and the bird cherry and common ash woods (Pruno-Fraxinetum) on the gleys, the elm and oak woods (Ficario-Ulmetum campestris) in the alluvia of major rivers, vega soil type, the cow-wheat oak and hornbeam woods (Melampyro-Carpinetum) on the plateaux and slopes with developed brown earths in three types differing according to the mineral composition of initial rocks, i.e. typical on loess, primrose on southern limestone slopes, woodrush on the slopes of silicate rocks, lime and oak wood (Tilio-Betuletum) on the terrace plateaux, gravelsands and shales with brown earth poor in minerals, hornbeam and maple woods (Aceri-Carpinetum) on steep scree slopes with ranker brown soil or rendzina, woodrush oak woods (Luzulo albidae-Quercetum) on markedly mineral-poor rocks - shales, quartzites, lydites with oligothropic brown earth, heather oak wood Calluno-Quaercetum) on steep rocky slopes of acid rocks, shales, quartzites, lydites, ranker soil type, molinia birch and oak woods (Molionic arundinaceae - Quercetum) on badly drained plateaux on pseudogley, woodrush beech woods (Luzulo-Fagetum) on the northern slopes of sandstones on higher sites of Prague basin, the hairy oak woods (Lathyro versicolaries - Quercetum pubiscentis) on southern slopes of limestones or diabases, soil type rendzina, swallow-wort and German catchfly oak woods (Cynancho-Quercetum + Viscario-Quercetum) on steep southern slopes of silicate rocks, soil type ranker, cinquefoil oak woods (Potentillo albae-Quercetum) on limestone, marlite and sandy marlites plateaux with variable soil moisture, soil type mull rendzina, grassy rocky communities (Festucion valesiaceae) on outcrops of limestones and basic silicate rocks, soils types rendzina or ranker, alison rock communities (Alysso-Festucion pallentis) on steep scarps of silicate rocks, soil type ranker.
The major part of the area of these natural communities were usurped by the city or various substitue non-forest communities or planted woods. In spite of that, however, all above mentioned types still exist except perhaps for the elm and oak woods which used to occupy the Vltava fluvial plain and whose traces can be found only in the Royal Game Preserve turned into a park. Practically all other communities have been preserved in the network of protected areas which will be described further on.
Apart from these forest communities there is in Prague a large group of non-forest communities ranging from natural rock, aquatic and river bank types over various man-influenced wood margins, bushes, pastures, mown meadows, orchards, to artificial parks, gardens, intensive field cultures and ruderal vegetation on dumps, construction sites, etc.
We shall deal with the most varied vegetation types when describing the individual protected areas.

At least 20 communities were described in markedly man-influenced areas to which detailed specialized study certainly would add many others. That, however, should form the object of another study of urban vegetation. In this work we shall concentrate on near-natural vegetation deserving protection and special attention.
In the past two decades a considerable decrement of even previously frequent species has taken place together with a change of structure of many plant communities, which resulted in the calls for some activites to stop these detrimental processes. A new field of nature protection originated - the care or management of protected areas. The State nature protection agency is publishing an extensive work at present - a manual of the care of protected areas according to individual communities or their groups.
In Prague special attention should be paid particularly to thermophilous lawns on rocks, concentrating most rare species, as well as valley meadows and wetlands. On these sites the traditional agricultural exploitation should generally proceed, i.e. the meadows should be mown, the thermophilous lawns grazed and protected against overgrowing with brushood (shrubs). Forest communities do not require regular interference, but circumspect managers who will assure reproduction by local seeds and in the ratio of principal wood species corresponding to the natural community structure. That means that e.g. in an oak and hornbeam wood there should be about 60 % of oaks and 30 % of hornbeams with an admixture of lime, beech, maple and pine trees, and not 80 % of pine trees with an admixture of leaf-tree species. Favourable structure of the tree level will assure adequate environment for the whole ecosystem of plants, animals and microorganisms without requiring any further care.

Also orchids, such as the white helleborine (Cephalanthera alba), can be found in Prague area.

Snow-drop windflower (Anemone sylvestris) grows on sunny shrubby slopes and forest steppes.

Aegonychon purpurocaeruleum grows on warm and sunny sites.

CONTENTS