BIODIVERSITY OF THE HERCYNIAN MOUNTAINS OF CENTRAL EUROPE

The vegetation of temperate Central Europe north of the Alps is mainly of low diversity broadleaf and conifer forest. The occurrence of three azonal habitat types: mires with their numerous microhabitats, the georelief of the karst and its deeply-cut river valleys, and ecological islands with a distinct vegetation near the treeline of the middle-mountains causes local areas of high diversity. These high species diversity spots are the result of an interplay between physical, biotic and historical factors. A model of an anemo-orographic system with its underlying factors is described to explain the high plant and animal diversity in the corries (glacial cirques) of the Hercynian mountains.

SUMMARY.-The vegetation of temperate Central Europe north of the Alps is mainly of low diversity broadleaf and conifer forest.The occurrence of three azonal habitat types: mires with their numerous microhabitats, the georelief of the karst and its deeply-cut river valleys, and ecological islands with a distinct vegetation near the treeline of the middle-mountains causes local areas of high diversity.These high species diversity spots are the result of an interplay between physical, biotic and historical factors.A model of an anemo-orographic system with its underlying factors is described to explain the high plant and animal diversity in the corries (glacial cirques) of the Hercynian mountains.

Introduction
Biodiversity is manifested at all levels of the biological hierarchy: from genes to species, communities and ecosystems (SOLBRIG, 1991;GROOMBRIDGE, 1992).Whilst shidies of diversity at the gene level require experimental procedures which can only be applied to a limited number of model organisms, at the species and community levels diversity is studied using observational-comparative methods (MAYR, 1982).The latter enables a satisfactory evaluation of regional and global diversity, and the management and conservation of biotic resources.An assessment of biological diversity in practice is therefore often reduced to observations and comparisons of species presence or absence.Identification of the centres of biodiversity (WWF & lUCN, 1994) and various hotspots of species biodiversity have received much attention lately.Most mountain regions, owing to their physical and biotic diversity, belong to the species-rich centres and hotspots.
The priorities identified at the EST Workshop at Monte Bondone in 1995 for European mountain biodiversity research were: (1) a synthesis of current data with regard to the biodiversity in mountain habitats in Europe, (2) an identification of gaps in scientific knowledge and (3) the initiation of cooperative research programmes.
The availability of data for synthesis is a result of centuries long natural history research in Europe.A cursory look at the data would reveal that both plants and animals showed a contrast between lowlands and uplands with regard to the number of species and variety of community types per unit area and how impacts of present-day immigrations and historical factors affected the speciation, immigration and survival of viable populations.In a wider context, the importance of mountain diversity for human society and in general, its influence on the development of natural history can be shown (JENÍK, 1996).
In Europe, the highest biological diversity is associated with the Pyrenees, Alps and Caucasus; i.e. the high-mountain systems situated at the transition zones between the temperate and submediterranean zones (MEUSEL et al., 1965).The Alps have a particularly long history of scientific exploration in western Europe (OZENDA, 1988) with an active natural history research predating the Linnaeus period.The geomorphological and plant diversity of the Alps with their c.350 endemic species of vascular plants (PAWLOWSKI, 1970) has much attracted botanists and plant sociology and the syntaxonomy of communities of the Zurich-Montpellier School were born in these mountains (BRAUN-BLANQUET, 1951).
In the scientific shadow of the Alps remain the so called middlemountains of Central Europe.These lower ranges (see map on the inner side of the cover in OZENDA, 1994) belong geologically to a much older Hercynian (Variscan) system than the Alps.They stretch from the Massif Central in France to the westernmost outliers of the Western Carpathians in Poland and Czechia.They rise only marginally above the altitude of natural tree growth today and provide excellent examples of refuges of arctic-alpine populations of the present Post-glacial era.They offer, in the absence of strong human impacts, a system to study the interaction between physical and biotic factors.These middle-mountains have also played an important role in the development of universities and other learned institutions of Germany, France, Austria, Czechia and Poland.

Brief historical notes
The exploration of species diversity in the Central European middlemountains began by the activities of herbalists L. Camerarius and P. Jesenius in the Ore Mountains at the end of the ló^'^ century (HEYNERT, 1964).C. SCHWENCKFELDT first published enumerations of biota occurring in the Sudetes in 1600.After the 30-year war, in the second half of the 18* century floristic research became active again (e.g.: MATTUSCHKA, 1776-1777).A unique scientific expedition of the Royal Bohemian Society into the Giant Mountains in 1786 (JIRASEK et al, 1791) returned with long lists of plants from species-rich sites.It also discovered new species for science, e.g.Poa laxa, a species later recognised as a typical component of the distant North American mountains (JENÍK, 1986).Numerous flora works covered the northern (Silesian) side of the Sudetes (for a list see JENÍK, 1961).
Comparative studies in the 19"^ century highlighted essential differences in species composition between lowlands and uplands and described the distribution of various formations (today's biomes) in certain mountain ranges.Botanical research had always been more advanced than zoology, mainly owing to the efforts of physicians, herbalists and apothecaries searching for medicinal herbs.Early exploration of wildlife was made by hunters and naturalists, who described game and predatory mammals, birds and reptiles, but modern zoological research can only be dated back to the beginning of the 19'^ century.The study of the invertebrate fauna -concentrating on some groups of insects-started much later (KIESENWETTER, 1847) and slowly, the difference in biodiversity between high-mountains and particular middle-mountain ranges became more apparent.
During the 20* century, a number of taxonomic summaries reconfirmed the high species-richness in some of the Hercynian ranges, particularly in those which rise above the timberline.A summary of their characteristics is given in the Appendix.Progress in animal and plant taxonomy and the availability of floristic data with a good coverage over the whole of Central Europe enabled comparative studies and the compilation of plant distribution maps (MEUSEL et al., 1965;1978).Other developments included small-scale vegetation mapping (MIKYSKA, 1968), description of communities (by using phytosociological relevés) and a classification of syntaxonomic units (OBERDORFER, 1977(OBERDORFER, -1992;;MORAVEC et al., 1983), and comparative ecological evaluations of mountain ecosystems, based on the latter (JENÍK, 1961).
Presenting an overview of the biodiversity is fraught with difficulty arising from Central Europe's centuries long political fragmentation.Administrative boundaries dividing ridges into sovereign territories have constrained field studies, separated collections of specimens and forced unnatural boundaries in mapping.For example, individual geographic (landscape) units were often divided and each side's biotic communities were described in local publications at opposite sides of borders, sometimes in different languages with the information seldom crossing the border.Research has been fraught v^ith semantic inconsistencies, and topographic names, nomenclature of plants and animals, and mapping units of vegetation have varied much.In addition, about half the 20* century has been affected by militarisation, the two World Wars and later by the erection of the Iron Curtain.
Biogeographical research suffered from the absence of unified toponyms and relevant topographical maps.The Central European middle-mountains still lack a consensus on oronyms (JENIK, 1998).For example, the prominent range situated along the border dividing Austria, Germany and Czechia is called Bohmerwald in German speaking Austria, but Hinterer Bayerischer Wald in Germany, and Sumava in Czechia.The usage of these oronyms often overlaps and much confusion is caused in the relevant data banks, regional literature and when an English equivalent is required (a suitable one for the above may be Bohemian Forest).Another lower range to the NW along the same national boundary is called Oberpfalzerwald on the German side, yet the Czech side bears the name Cesky les, a homonymous equivalent of the Austrian name Bohmerwald.It is worth noting that in the maps of Claudius Ptolemaios the same area was called Silva Gabreta, a forgotten unifying name only recently reintroduced for a new natural history book series.Owing to the above, information about the diversity of species, communities and ecosystems, is scattered in the scientific literature of the four neighbouring countries: Austria, Czechia, Germany and Poland.Only a few large-scale synthetic works, such as those of HEGI et al. (1966 et seq), TUTIN et al. (1964-1983), FIRBAS (1949;1952) and ELLENBERG (1996) provide integrated information over the entire area.Two recent publications by UNESCO and lUCN (PRICE, 1995;lUCN, 1995) have also given a transboundary treatment of the Hercynian middle-mountains.

Species diversity in Central Europe
There are about 80000 known species of all organism groups (Table 1) in the Czech part of Central Europe (e.g.VAVROUSEK & MOLDAN, 1989;PLESNÍK, 1999).This is only about 5 % of the world total number of species described so far (GROOMBRIDGE, 1992).In temperate Europe, the most species rich groups (fungi and invertebrates) are associated with old growth forests and can have a high richness within a single community, i. e. high alpha diversity (sensu WHITTAKER, 1970).However, old growth forest stands are rare and the majority of the remaining woodlands have been transformed into monodominant stands with few tracheophyte species.Azonal non-forest ecosystems, whose species composition substantially varies along environmental gradients and over patchy soils (beta diversity sensu Whittaker, 1970), also have a high biodiversity.The diversity of autotrophic tracheophytes may be used as an estimator of overall biodiversity and the non-forest forbs and graminoids with their numerous associates can provide a proxy in estimating species-richness in the mountains.
Closed woodlands covered > 90 % of the landscape north of the Alps (domaine Centre-Européeen, sensu OZENDA, 1994)   woodlands in the lowland and colline belt, (2) closed beech and fir forests in the lower montane belt, and (3) monodominant spruce taiga in the upper montane belt.The forest formations comprised about 35 tree species, 300 vascular herbs, and correspondingly low numbers of consumers at the lower trophic levels.Actual and potential composition of these forests is described in detail in the phytosociological (e.g., OBERDORFER, 1977OBERDORFER, -1992;;ZLATNÍK, 1959;ELLENBERG, 1996;MUCINA etal, 1993;MORAVEC et al, 1983) and palynological literature (FIRBAS, 1949;1952;HUNTLEY & BIRKS, 1983).The Pleistocene glacial periods inhibited migration and the flora and fauna became relatively impoverished in Central Europe in contrast to the more species-rich Eastern Forests of North America.
The floodplain woodlands and colhne oak-hornbeam woods at lower and warmer altitudes have been reported to contain 50 vascular plant species per relevé (about 400 m^ in size), however, most of the zonal vegetation in the foothills of Hercynian mountains consists of oligotrophic oak forests, beech forests and spruce taiga, with < 20 vascular plant species per relevé.There is a high beta diversity in azonal woodlands along deeply-cut river valleys and on limestone (karst).On hill sides, the north facing slopes tend to host psychrophilous beech (Fagus sylvatica) communities, whilst the warm southern slopes on limestone host durmast-oak (Quercus pubescens) woods where plant and animal species of a diverse geographical origin occur together.
The biodiversity of the Central European landscape is higher in patchy and treeless azonal habitats, where plants and animals do not face the adversity of closed-canopy shade and root competition by trees is reduced.
The closed woodlands of Central Europe become patchy naturally in extreme environments such as the dry and hot south-facing slopes along the river valleys, in the karst areas and on exposed cliffs of volcanic hills.These xero-thermic habitats are found along the large rivers, such as the Berounka, Danube, Sázava, Saale, Vltava and Weser, on limestone, e.g.: Swabian Jura, Bohemian Karst, Moravian Karst, in the basaltic Doupov Hills and on the neovolcanic cones of NW Bohemia (Ceské Stredohorí) in the rain shadow of the Ore Mountains.The treeless patches are dominated by Festuco-Brometea grasslands, containing a mixture of relics and forerunner species, including some continental elements left from the Late Glacial when this biome was widespread in Central Europe.
Waterlogging, particularly in depressions and areas of permanent springs and mires produces a variety of wetlands which may occur locally in forests.There is a variety of life forms present in wetlands which interact with the physical environment and influence microhydrology and microtopoclimate, and thus create favourable conditions for enhanced beta diversity.Soligenous mires of the Scheuchzerio-Caricetea fuscae class (fens) and ombrogenous mires (c) Consejo Superior de Investigaciones Científicas Licencia Creative Commons 3.0 España (by-nc) http://pirineos.revistas.csic.es of the Oxycocco-Sphagnetea class (bogs) make remarkable contribution to biodiversity in Central Europe, particularly with regard to bryophytes and invertebrates.For example, on the Cervené Blato bog in South Bohemia, SPITZER & JAROS (1993) identified 570 species of butterflies over an area of less than 3 km^.The drying out of these wetlands creates favourable conditions for tree growth, and thus a high reduction in beta diversity.The adverse effects of waterlogging on trees may combine with effects of low temperature in the montane and subalpine belts of the Hercynian mountains.This is the case for mires and flushes in the High Sudetes (particularly in the Giant Mts.), where numerous arctic-alpine plant and animal species have survived the pressures of forest succession in the Holocene and contribute to today's biodiversity.
Cold wind-exposed habitats, particularly at high altitude with a short growing season can prevent the successful establishment of trees by delaying the hardening of the xylem tissues.Common in the neighbouring Alps and Western Carpathians, this treeless bald or alpine tundra is a rarity in the Hercynian middle-mountains.They mostly occur as small treeless islands on top of some ridges and peaks, in snowbeds and corries.Some of them can be viewed merely as azonal islands within the montane belt: e.g.Plesné Lake, Cerné Lake, Certovo Lake and Gross Arber-See corries in Bohemian Forest, the Zechengrund in the Ore Mts., or the summit bald of the Harz.However, the larger treeless areas on top of the Vosges, Black Forest, Giant Mts., Snow Mts. and Jesenik Mts.form a true altitudinal belt, sometimes referred to as subalpine or even alpine.Their diversity is best reflected by the number of habitats and communities.For example, in the three ranges of the High Sudetes, about 70 plant communities have been distinguished in 11 phytosociological classes (habitats): Asplenietea trichomanis (crevices), Thlaspietea rotundifolii (scree), Juncetea trifidi (summit tundra), Salicetea herbaceae (snow beds), Mulgedio-Aconitetea (tall-herb communities), Montio-Cardaminetea (flushes), Scheuchzerio-Caricetea fuscae (fens), Oxycocco-Sphagnetea (bogs), Nardo-Callunetea (mat-grass and heath communities), Betulo carpaticae-Alnetea virids (subalpine scrub), and Vaccinio-Piceetea (krummholz).The species richness of these habitats is well documented in floristic and faunistic works; SOUREK (1969) enumerated 1150 vascular species in a single range of the Giant Mountains, which equals half the total estimated for Czechia (Table 1).

The human vegetation history of the Hercynian mountains
Human-induced fragmentation of the continuous forest cover in the warm lowlands of Central Europe began in the Neolithic, about 5,000 B.P. resulting in today's mosaic of natural, semi-natural and cultivated forests, pastures, meadows, arable land and patches of treeless clearings (for a summary see ELLENBERG, 1996).Forest clearing and the expansion of agriculture have progressively moved into the montane belt and to the ridges of the Hercynian mountains.Pasturing at the summits of the Vosges has been mentioned as early as the 9* century (SCHMITT, 1963), whilst the uplands of the High Sudetes were not exploited until about the 16* century (LOKVENC, 1978).Using the evidence of archives and old charts, JENÍK & HAMPEL (1992) pointed out some differences in the exploitation of summit tundra on various estates in the Jesenik Mts., where the 16th century, too, appeared to be the beginning of pasturing.The application of artificial forest regeneration, cultivation of monodominant stands of Norway spruce (Picea abies (L.) Karsten) and Scots pine {Pinus sylvestris), and the introduction of exotic tree species such as Pseudotsuga menziesii, Pinus strobus, Robinia pseudoacacia for example have caused large changes in the foothills of Hercynian mountains over the past 200-300 years.The intensive management has not caused forest loss in the montane belt in most of the Hercynian ranges, but species diversity has declined mainly through the expansion of coniferous stands.
Altitudinal zonation in the Hercynian mountains differs in the west from that in the east.In the Vosges and in the Black Forest, European beech (Fagus sylvatica) and silver fir {Abies alba) had primarily dominated much of uppermost montane belt up to the tree-limit, however following tree cutting, burning and air pollution it has been transformed into monodominant plantations.In contrast, in the Bohemian Forest, the Ore Mts. and Sudetes, beech forests seldom reached an altitude of > 1000 m and coniferous taiga with Norway spruce predominated up to about 1300 m.However, forest clearing and logging, followed by either natural regeneration or plantation in the last 300 years have resulted in monodominant spruce stands over most of these mountains today.The loss of broadleaf stands caused an impoverishment of soils and reduced both below-and aboveground species richness (preliminary data on fungi and bacteria are available at Charles University).Wind throws followed by bark beetle outbreaks were another factor in changing forest composition with prominent effects on biodiversity.
Norway spruce, European beech and silver fir form a krummholz in the transition towards the treeline in many Hercynian ranges where there is no naturally occurring dwarf pine {Pinus mugo).Monodominant stands of P. mugo form a krummholz only in the Giant Mountains with small patches also in the Bohemian Forest and Iser Mts.Remarkably, the Jesenik Mts. were never colonised by dwarf pine, though it is widespread to the west, in the Giant Mts. and to the east, in Babia Góra (the westernmost Carpathian range with

Pinus mugo).
The are no altitudinal limits to tree growth in the Ore Mts. and their species-rich Zechengrund is probably only a small island in the snowrich leeward side (see below).
The position of the treeline and the presence or absence of the competitive dwarf pine have played an important role in the development of biodiversity in the Hercynian mountains (JENÍK & LOKVENC, 1962).Not only altitude, but general relief and topoclimate (irradiation, wind action, duration and distribution of snow, snow creep and avalanches) have diversified the pattern of the alpine-like belt with its wide range of plant and animal species from either the Alps and the boreal/subarctic region (SOUKUPOVÁ et al, 1995).In the mid-Holocene period, marked by the expansion of Central European woods above, their current altitudinal limits, only the highest summits, steep flanks and corries remained treeless.Treelessness has been a prerequisite for the development and maintenance of fragile plant populations and communities of alpine character.In a similar context, CARBIENER (1966) prefers to write about subalpine vegetation in the Vosges, and BOGENRIEDER et al. (1982) have coined the term subalpine island for the highest area of Feldberg in Black Forest.
The long-term maintenance of the local alpine-like areas without relict forest species and their continued treelessnes remain a puzzle for the palaeoecologist.Palynological data have suggested that during the climatic optimum, about 5,000 years ago, forest vitality in Central Europe increased and the alpine timberline ascended 200 to 400 m above its present-day position (FIRBAS, 1952;de VALK, 1981;HÜTTEMANN & BORTESCHLÀGER, 1987).This means that all Hercynian ranges would have been covered by forests and their heliophilous arctic-alpine populations should have become extinct.Also, there would have been no place for the microevolutionary processes which resulted in the differentiation of some non-forest plant taxa in the Holocene period (for details see JENÍK, 1983).

The causes of the distribution pattern of biodiversity
As a whole, the Hercynian mountain ranges lack high altitude, the diversity of rocks, large areas of limestone, and complexity of relief, they only exceptionally surpass the natural tree-limit, and their acid, nutrientpoor parent rocks seldom create a fertile substratum for eutrophic ecosystems.This is reflected in the species-poor zonal vegetation with a small number of tree species and few competitive ferns and grasses, ericaceous shrubs and a modest cryptogamic flora.The fauna is similarly species poor.However, there are some localised centres of high biodiversity in certain localities which harbour enhanced numbers of PIIUNEOS 151-152 species, many infraspecific taxa, and curious hybrids between parents derived from ecologically distant habitats.
An example of localities which repeatedly appear in floristic and faunistic lists is the three ranges of the High Sudetes.The corries (or cirques) of KoteLné Jámy, Labské Jámy, Sniezne Kotly, Kotly of Great and Little Staw in the Giant Mts, or Velká Kotlina corrie in the Jesenik Mts. have several hundreds of vascular plant species, whilstthe"^species-poor communities on neighbouring slopes are composed of only a dozen vascular species (JENÍK et al., 1983a;b).The above corries also have a high number of mosses, hepatics, molluscs and insects.Environmental and phytosociological analyses (JENÍK 1961;JENÍK et al., 1980) have identified some common features in the topographical position of these species-rich sites.They are mainly (i) on east-facing slopes at the eastern margin of large summit plateaux or on the eastern side of prominent saddles, (ii) across the summit plateaux on the adverse side of a prominent funnel-shaped valley, (iii) in the hollows of corries or snowbeds, (iv) situated under prominent cornices, covered regularly by deep snow drifts and affected by frequent avalanche action (JENÍK, 1990).
The driving force behind this special biodiversity pattern is the prevailing westerly winds, a feature well documented by summit meteorological stations on Snezka Peak and Szrenica (MÍGALA et al., 1995).The westerlies are streamlined and accelerated in funnel shaped windward valleys, and sweep across the corresponding summit plateau or saddle areas.This wind action is documented by flag-trees, unilaterally eroded turf and ablation forms in the snow surface in winter.Over the sheltered lee slopes, the laminar air flow changes to turbulent eddies, a process clearly detectable by the movement of clouds, airborne snow crystals and by the deposition of drift snow (STURSA et al., 1973).In summer, deposition of other airborn particles, such as soil, litter and seeds has also been documented.Similar topographical configuration and related air currents appear in the summit areas of all Sudetic ranges and there are 10 prominent areas of enhanced species diversity related to them.JENIK (1961) has described a model called anemo-orographic system, which consists of three interdependent components: (1) windward funnel-shaped valley, (2) acceleration summit zone, and (3) leeward turbulence zone.The validity of this model has later been confirmed in the Vosges (CARBIENER, 1966;1969;de VALK, 1981), in the Bohemian Forest (SOFRON & STEFAN, 1971) and in the Feldberg region in Black Forest (JENÍK, unpublished).It is the leeward turbulence zone that coincides with the centres of high biodiversity.Current weathering and locally outcropping base-rich rocks, which are kept bare by the secular action of avalanches and water erosion improve nutrient availability at these sites.In the summer, dissected turf and exposed soil are invaded by seed and spores transported Despite the avalanches and erosion by melt water the leeward habitats of the anemo-orographic systems have, maintained a stable microhabitat diversity and, in the course of millenia, accumulated a genetically diverse assemblage from rather different mountain and sometimes lowland ecosystems.Relicts from the Late Glacial and early-Holocene grow together with sub-thermophilous species of the mid-Holocene.These sites function as micro-evolutionary workshops where gene recombination and hybridization produce new infraspecific taxa or microspecies (JENIK, 1983).The corries of the Sudetes, for example, have been the speciation centres for the apomictic Hieracium genus (20 endemic species).The Velká Kotlina in the Jesenik Mts., is in the lee of a double anemo-orographic system, and has accumulated about 500 vascular plant species (some of them have recently become extinct).It also has a rich vertebrate and invertebrate fauna, which makes this place the most species rich locality in the whole of the Hercynian mountains of Central Europe (JENIK et al., 1983a;b).Similarly, a prominent anemoorographic system makes possible the presence of biogeographically outstanding species in the back wall of the corrie near Great Arber Lake in the Bohemian Forest (JENÍK et al, 1998).

92( c )
Consejo Superior de Investigaciones Científicas Licencia Creative Commons 3.0 España (by-nc) http://pirineos.revistas.csic.essometimes from afar, thus further increasing the richness of flora and fauna.Treelessness has been maintained by avalanches, which even occurred during the climatic optimum of the mid-Holocene due to snow swept from the large summit plateaux.

Table 1 .
by the end of the late-Holocene.Three forest formations dominated: (1) mixed broad-leaved Estimated numbers of indigenous species in Czechia.Data are from various sources.