Around 40% of the Slovak territory is covered by forests of diverse composition. Photo: Š. Macko

Originally, almost the entire territory of present Slovakia was covered by forests. Open areas were an exception sustained by extreme ecological conditions. For instance, subalpine brushes with dwarf pine (Pinus mugo) extend in climatically adverse areas above the upper timberline and in higher elevations give way to alpine meadows.

Yellow adonis (Adonis vernalis) is a representative of the forest-steppe flora. Photo: P. Plesník

Meanwhile, on the southern sun-exposed slopes with shallow soil profiles in the warm areas of the Slovak territory steppes and transitive forest-steppe forms have developed due to an intense evapotranspiration and relatively high soil temperatures. Small areas without forest are also swamps, riverine gravel deposits, localities with saline soils as well as sand dunes. On the chernozem soil in warm lowlands presumably true steppes existed too but have disappeared as a result of land cultivation.

The current character of Slovak forests reflects the expansion of vegetation into this area following the last glacial age. It is based on the balance that established itself between the environmental conditions on one side and the overlapping ecological amplitudes of expanding species on the other side. It is noteworthy that the fir - beech belt expanded to this territory no earlier than in the atlantic, i. e. 5000 - 3000 years B.C.. This belt wedged in between the zones occupied by spruce (Picea abies} and oak (Quercus petraea).

Vegetation stages

Due to the shape of the Slovak territory and its "alignment" along parallels rather than meridians, it is far more the arrangement of altitudinal vegetation stages than the lattitudinal vegetation zonality that gives rise to the vegetation differentiation. According to the climatic conditions changing with the rising altitude the following seven forest vegetation stages have been distinguished:

1. oak 100 - 400 m a.s.l.
2. beech-oak 200 - 550
3. oak-beech 250 - 700
4. beech 450 - 800
5. fir-beech 650 - 1050
6. beech-fir-spruce 850 - 1300
7. spruce 1100 - 1550
8. (dwarf pine) 1450 - 1900

The constituing tree species or carriers of the vegetation stages altitudinal arrangement are therefore durmast oak (Quercus petraea), European beech (Fagus sylvatica), silver fir (Abies alba), Norway spruce (Picea abies) and dwarf pine (Pinus mugo). The above vegetation stages are also differentiated by typical plant species.

First three vegetation stages are accompanied by dominating grass species with high demand on light. At the same time, the occurence of xerophilous grass species marks the first vegetation stage whereas both the first and the second stages feature typically abundant presence of thermophilic oakwood herbs. Beside oaks (mainly Quercus petraea and Quercus cerris) and beech, also hornbeam (Carpinus betulus), field (hedge) acer (Acer campestre) as well as small and large-leaved lime-tree (Tilia cordata, T. platyphyllos) make themselves felt in these stages.

An oak - hornbeam forest. Photo: P. Plesník

In the 3^rd vegetation stage it is already intensively shading beech that begins to assert itself. Parallel to that, the role played by species able to withstand shade and requiring higher soil and air moisture levels increases whereas the proportion of oak and its accompanying plants diminishes. Beech along with so-called beechwood species find their optimum in the 4^th vegetation stage, but remain abundant in both the 5^th and 6^th stages as well.

In the 5^th stage, along with beech also fir becomes an important species, accompanied by submountain and mountain species, ferns a and tall herbs well adapted to lower temperatures, a shorter vegetation period and species demanding higher soil moisture levels. In the Carpathian forest, sycamore maple (Acer plseudoplatanus), common ash (Fraxinus excelsior) and wych elm (Ulmus glabra) have also established themselves as an important forest admixsture. These forests belong to the most productive ones in Slovakia.

Mountain spruce forests atop Poľana Mts., a former volcanic massif. Photo: V. Pichler

In the 6^th stage beech is weaker and less competitive compared to fir and spruce. Spruce eventually takes over in the 7^th stage with a typical admixture of rowan (Sorbus aucuparia) or larch (Larix decidua) whereas species from the lower stages are entirely absent due to harsh climatic conditions and a very time-limited vegetation period. In the 6^th and 7^th stages subalpine light - requiring species demanding a high and sustained soil humidity are present too, even though they only descend over here from the 8^th stage.

Upper timberline in the Vysoké Tatry Mts. (High Tatras). Photo: P. Plesník

Along the upper timberline (around 1450 m a.s.l.) spruce is no longer able to establish a closed canopy and its stands gradually give way to dwarf pine (Pinus mugo) stands.

Upper timberline in the Belianske Tatry Mts. Photo: V. Pichler

The above stated scheme of the vegetation stages vertical arrangement doesn't apply fully in Slovakia's highest mountains, in the High Tatras. Massive and high mountain ranges extending above the upper timberline feature an increased continentality, which doesn't meet ecological demands of fir and beech that prefer a more oceanic climate. On the southern slopes of the High Tatras beech is not present at all (unlike on the northern side, where islands of beech stands can be found) and fir is rather rare. At the same time, spruce forms forests from the bottom of the depressions up to the upper timberline that reaches 100-250 m higher than in other Slovak mountains due to higher summer temperatures. Occassionally, spruce is accompanied by more windbreak and windthrow - resistant larch (Larix decidua), cembra pine (Pinus cembra), white birch (Betula pubescens) and rowan tree (European mountain ash, Sorbus aucuparia). Along the upper timberline and above it there is a higher concentration of cembra pine individuals that stick conspicuously out of the dwarf pine carpets. Quite differently, fast-growing spruce trees were planted on the Polish High Tatras' northern slopes during the 19th century, following the clear-cutting of the original beech and fir forests (a more oceanic or less continental climate).

However, it must be stressed that such a vertical arrangement of vegetation stages exists in full scale only on normally developed soils with rain water supply.

Plant and tree communities with an azonal and less pronounced zonal character

Rank vegetation lines the Danube's dead arm (backwaters) with an adjacent flood plain forest. Photo: P. Plesník

So-called azonal communities come on sites influenced by ground water or sites bearing poorly developed soils. Parts of lowlands and rivers alluvia were originally covered by extended flood-plain forests: willow-poplar forests with white willow (Salix alba) and crach willow (Salix fragilis) as well as with white poplar (Populus alba) or black poplar (Populus nigra) settled the areas adjacent to meandering streams that are subject to long lasting inundation during vegetation periods. On sites with stagnant water black alder (Alnus glutinosa) prevailed.

A floodplain forest with black alder. Photo: P. Plesník

Localities, where floods usually last shorter, sustained hard-wooded floodplain forests featuring a dominant common (English) oak (Quercus robur) along with common ash (Fraxinus excelsior), narrow-leaved ash (Fraxinus angustifolia), European white elm (Ulmus laevis), smooth-leaved elm (Ulmus campestre), field acer (Acer campestre) and numerous shrubs. In mountain areas smaller streams are usually lined by common alder (Alnus glutinosa) along the lower course and by speckled alder (Alnus incana) along the upper course.

Other types of forest communities occur on less developed talus stony soils, rich in nitrogen and having enough moisture. In hills at lower elevations these forests are constituted by field acer (Acer campestre), Norway maple (Acer platanoides), large-leaved linden (Tilia platyphyllos), small-leaved lime-tree (Tilia cordata) and hornbeam (Carpinus betulus). In mountains they are replaced by sycamore maple (Acer pseudoplatanus), common ash (Fraxinus excelsior) and wych elm (Ulmus glabra).

Tartar bread plant (Cambre tatarica) - a steppe runner

Still other plants and trees grow on dry shallow, well draining soils with low water retention capability, mainly on limestone, dolomite or volcanic slopes adjacent to lowlands, where there is a mosaic of communities with xerothermophilous herbaceous and shrub species such as corneham cherry (Cornus mas) or mahaleb cherry (Cerasus mahaleb) altering with stands of pubescent oak (Quercus pubescens) or Turkey oak (Quercus cerris).

Relict sand dune with a Scotch pine stand. Photo: P. Plesník

The common (Scotch) pine (Pinus sylvestris) stands with an admixture of durmast oak (Quercus petraea) can be regarded as a specialty ) on wind blown sands and dunes containing very little nutrients and suffering from the lack of water that drains rapidly through sand with a high hydraulic conductivity. It is interesting to see that due to specific physical properties of sand, the infiltrating water cools off, springs again at the foot of sand hills and creates favourable conditions for psychrophilous plants, such as Siberian iris (Iris sibirica), a glacial relict.

Alpine aster. Photo: P. Plesník

Pines also grow on extreme mountain sites e.g. steep rocky galleries where other tree species are unable to establish closed canopy. These stands represent a relict of the boreal and preboreal periods and feature lots of typical plant species, for instance mountain avens (Dryas octopetala).

Statice gmelinii is typical of saline sites. Photo: P. Plesník

In several depressions of warm areas with a low precipitation, where - due to capillarity - ground water reaches the soil surface and evaporates, salts precipitate in the topsoil. Such places with saline soils can be occupied only by halophilous plants that can resist a high salts concentration, e.g. Statice gmelinii (Limonium gmelinii).

Last but not least, there are alpine plants growing above the carpets of the dwarf pine vegetation stage. They had to adapt to special and harsh climatic conditions such as low temperatures, short vegetation period, long-lasting snowpack, strong UV radiation etc.. Such factors encouraged diverse mat-forming, pillow-like, carpet like or lane-like growth forms and an intense coloration functioning as a kind of UV filter. Some of these adaptations can be seen in plants like mountain avens (Dryas octopetala), Alpine Butterwort. (Pinguicula alpina), Edelweiss (Leontopodium alpinum), moss campion (Silene acaulis), least primrose (Primula minima), alpine buttercup (Ranunculus alpestris), alpine aster (Aster alpinus) etc..

Daphne arbuscula. Photo: P. Plesník

Furthermore, a couple of endemites have their home in Slovakia. One of them is a paleoendemic species Muran daphne (Daphne arbuscula) growing in the relict pine and pine - larch stands, another one is a neoendemic golden drop of Turňa (Onosma tornense) that can be found in the karstic area.

To sum it up, 41% of the Slovak territory is covered by forests. Despite an advanced forest management (or rather thanks to it), a large portion of original forest communities has been preserved up to the present day. Above all, indigenous tree species have never been substituted by spruce on a scale comparable with many other European countries.

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