VegetatIon patterns of dry grasslands and rocky grounds on VIdlIč MountaIn (southeastern serbIa)

: This paper studies vegetation patterns of dry grasslands and rocky grounds on the limestone terrain of Mt. Vidlič, which borders the southern edge of the Balkans Mountain in Serbia, known as Stara planina. Having conducted field research, we presented the obtained results in the form of a phytosociological table. Dry grassland and rocky ground vegetation belongs to the familiar alliances of Festucion valesiacae (Festuco-Brometea) and Seslerion rigidae (Festuco-Seslerietea). Phytosociological data were analyzed using cluster analysis and evaluation of biodiversity indices. The stands of dry grasslands and rocky grounds were classified according to their floristic composition. Altitude proved to be the major factor in their grouping by floristic similarity. In other words, there is an increase in biodiversity with an increasing altitude. The importance of dry grasslands and rocky grounds of Mt.Vidlič lies primarily in their role in erosion control, but their diversity makes them an important source of medicinal herbs and grazing land.

Захвалница: Овај рад урађен је у оквиру пројеката Министарства просвете, науке и технолошког развоја Републике Србије ОИ 171025, ОИ 173029 и TР 31070. Желели бисмо да изразимо нашу искрену захвалност др Бојану Златковићу (Природно-математички факултет, Ниш) због његових критичких коментара овог рада. Abstract: This paper studies vegetation patterns of dry grasslands and rocky grounds on the limestone terrain of Mt. Vidlič, which borders the southern edge of the Balkans Mountain in Serbia, known as Stara planina. Having conducted field research, we presented the obtained results in the form of a phytosociological table. Dry grassland and rocky ground vegetation belongs to the familiar alliances of Festucion valesiacae (Festuco-Brometea) and Seslerion rigidae (Festuco-Seslerietea). Phytosociological data were analyzed using cluster analysis and evaluation of biodiversity indices. The stands of dry grasslands and rocky grounds were classified according to their floristic composition. Altitude proved to be the major factor in their grouping by floristic similarity. In other words, there is an increase in biodiversity with an increasing altitude. The importance of dry grasslands and rocky grounds of Mt.Vidlič lies primarily in their role in erosion control, but their diversity makes them an important source of medicinal herbs and grazing land.

VegetatIon patterns of dry grasslands and rocky grounds on VIdlIč MountaIn (southeastern serbIa)
Key words: Mt. Vidlič, dry grasslands, rocky grounds, floristic composition, index of biodiversity ject of numerous studies (Harrison et al., 2003;Alard et al., 2005). Their formation, floristic composition and structure have been determined by different anthropogenic, climatic and edaphic factors (Diklić, Nikolić, 1964).
The stands of dry grasslands and rocky grounds growing on limestones of eastern Serbia belong to Festucion valesiacae Klika 1931 (class Festuco-Brometea Br.-Bl. et Tüxen ex Soó 1947) and Seslerion rigidae Zoly. 1939 (class Festuco-Seslerietea Barbero et Bonin 1969) alliances. Although they are markedly steppe in character, they have certain Mediterranean and sub-Mediterranean floral elements in the composition, which points to complex living conditions prevailing in these areas (Diklić, Nikolić, 1964).
Thermophilic meadows, grasslands and rocky grounds on Mt. Vidlič were formed in the belt of oak forests after they had been felled, especially after a period of grazing which followed the fellings. They can be also found at higher altitudes in the belt of south-facing beech forests during the research conducted on the mountain of Vidlič, it turned out that the data obtained on the floristic composition and ecology of xerophilic meadows and grasslands could contribute to the results obtained in earlier studies of similar communities on limestone in eastern Serbia Jovanović-Dunjić (1955, 1956, Danon (1960), Diklić (1962), Diklić, Nikolić (1964), and in central and western Serbia where they occur in the form of fragments of extrazonal steppe vegetation (Marković, 1982(Marković, , 2007. The most common associations of dry grasslands and rocky grounds on Mt. Vidlič are: Carici humilis-Stipetum pulherrimae R. Jov. 1955., Potentillo-Caricetum humilis R. Jov. 1955., Sanguisorbo-Festucetum vallesiacae, Bromo-Festucetum valesiacae, Galieto-Festucetum valesiacae and Andropogono-Danthonietum calycinae. A great deal of attention was paid to the areas of dry grassland and rocky ground in highly eroded regions, where Euphorbio myrsiniti-Botrichloetum (Chrysopogoni-Satureion) community occurs, representing the final stage in the degradation of the thermophilic forest as one of the most important broader represented associations. These communities are composed of plants adapted to dry and warm sites with a shallow layer of soil that is poor in organic and mineral materials.
Carici humilis-Stipetum pulherrimae association has two edifying species: Carex humilis and Stipa pulherrima. A highly polymorphic species Stipa pulherrima with a significant number of subspecies and varieties is commonly found in dry, sunny and rocky areas of the southern and eastern regions of Europe, mainly on limestone (Jovanović-Dunjić, 1955). In Serbia, this association was described by Jovanović-Dunjić (1955) on Mt. Suva Planina. It was recorded on the southern slopes of Mt. Rtanj below its highest peak named Šiljak (Jovanović-Dunjić, 1956). It was further found by Diklić and Nikolić (1964) on Svrljiške mountains. With its great abundance and considerable coverage, golden feather grass (Stipa pulherrima) suppresses other species that make up this community. Golden feather grass (Stipa pulherrima) has virtually no nutritional value, so these grasslands are not used for grazing. However, it has an important role in soil binding on limestone rocky grounds.
Potentillo-Caricetum humilis is a forest community that occurs on gentler south-facing slopes of Mt. Vidlič which are at higher altitudes (about 1000 m) of the following localities: Basarski kamik and Golemi vrh above the villages of Gulenovci and Visočki Odorovci. The soil is loose, porous and quickly-drying. It is more compact and deeper than the soil in the association of Carici humilis-Stipetum pulherrimae. Site features and characteristics of the association of Potentillo-Caricetum humilis are very similar to the associations of the same name on Mt. Suva Planina (Jovanović-Dunjić, 1955) and Mt. Rtanj (Jovanović-Dunjić, 1956), and to artemisietosum subassociation on Leskovik (Diklić, 1962) and Svrljiške Mountains (Diklić, Nikolić, 1964), which shows that this community in eastern Serbia is primarily affected by the characteristics of the soil and topography. Potentillo-Caricetum humilis association is used as small livestock pasture in summer months. This plant community has a very important role in binding the soil on the southern slopes of the mountain, preventing landslides and removal of shallow and crumbly topsoil.
These diverse dry grasslands and rocky grounds have traditionally been used for livestock grazing, which was particularly the case in the last century. Today, rich diversity of meadow, grassland and rocky ground vegetation is an important source of medicinal (Marković et al., 2010), especially aromatic herbs (Marković et al., 2009), which have a wide and varied application in medicine, pharmaceuticals, cosmetics, perfume and food industry.

Study area
Vidlič Mountain is located in the southeast of Serbia, north of the river Nišava and belongs to the municipalities of Pirot and Dimitrovgrad. It stretches from the northwest to the southeast up to the Bulgarian border and from there extends through its territory all the way to Sofia Valley. Mt. Vidlič belongs to the Balkan mountain range. The mountain is characterized by dynamic topography, sloped terrain and vast barren areas that are exposed to strong erosion processes.
The whole limestone area of Mt. Vidlič is characterized by dry skeletal soil developed over deep parent rock. The prevailing soil type is nutrient-poor, calcareous rendzina at different stages of soil development. Clear-cutting and the subsequent period of grazing resulted in the formation of many types of meadows, grasslands and xerophilic vegetation of eroded rocky slopes. The marked species diversity of limestone grasslands is largely associated with low availability of plant nutrients in the soil and long-term species immigration dynamics (Poschold, Wallisdevries, 2002;Schrautzer et al. 2009).

Field research
Field studies of dry grassland and rocky ground vegetation on Vidlič Mountain, southeastern Serbia were conducted in 2008, 2009 and 2010. The plant material collected during the field research was labeled and preserved in the "Herbarium moesiacum Niš", Department of Biology and Ecology, Faculty of Sciences, University of Niš-HMN.
Categorization of the collected plant material was performed according to Josifović (1970Josifović ( -1986 and Velčev (1982Velčev ( -1989, and the nomenclature was done in accordance with Flora Europaea nomenclature system (Tutin, 1964(Tutin, -1980(Tutin, , 1993. Phytosociological studies of dry grassland and rocky ground vegetation on Mt.Vidlič were carried out using the method of Braun-Blanquet (1964). The results are presented in the form of a phytosociological table.
All the localities were georeferenced using Ozi explorer software and plotted on the map (Fig-ure1) using DIVA-GIS (5.2 software) (Hijmans et al., 2005).

Analysis of phytosociological data and diversity
The obtained phytosociological data were analyzed using the classification method (WPG-MA) of Statistica 8.0 software package (StatSoft, 2007).
The combined cover-abundance value was estimated for each species in a plot after they had been transformed into the numeric scale proposed by Westhoff and van der Marel (1973). Alpha diversity, or the species diversity within the smallest units, was calculated using `Flora` software package (Karadžić, Marinković, 2009). Species richness (the total number of species) and Simpson's diversity index (Whitaker, 1972) that includes species evenness were also calculated.

research results
Dry grasslands of Sanguisorbo-Festucetum vallesiacae type were recorded at the site of Basara at an altitude of 900 m, with Sanguisorba minor as the dominant species and substantial presence of wild strawberry (Fragaria vesca) (Table 1).
Thermophilic grasslands of Bromo Festucetum vallesiacae type occur over large areas of south-western and western slopes of Mt. Vidlič, at the following sites: Vučje (490 m), Crni vrh (810 m, 890 m) and Izvor (490 m) (Table 1). Dominant species Festuca vallesiaca and Bromus squarrosus are typical of dry meadow and grassland sites.   (Table 1), and they are very similar in species composition to the thermophilic meadows of the same name on the mountain of Ozren (Diklić, 1962) at similar low altitudes, whereas they are less similar to the thermophilic meadows of the same name on the mountain of Rtanj (Jovanović-Dunjić, 1956), where they were recorded at higher altitudes (800-1000 m).
The importance of Sanguisorbo-Festucetum valesiacae at Basara site, Bromo Festucetum valesiacae at Vučje, Crni vrh and Izvor sites and Galieto Festucetum valesiacace at Vučje and Izvor sites as a source of livestock food reduces the presence of certain chamaephytic, aromatic, toxic and weed species, although these phytocoenoses are used for early spring grazing when the dominant and most abundant species Festuca valesiaca is still young.
Andropogono-Danthonietum calycinae was recorded at Vučje (490 m) and Izvor (489 m) (Table 1), and its floristic composition is similar to the plant community of the same name on Stara Planina (Mišić et al,, 1978), to Danthonietum calycinae on Ozren Mountain (Diklić, 1962), where it was formerly used as agricultural land and to Asperuleto-Agrostidetum vulgare on Rtanj Mountain (Jovanović-Dunjić, 1956). The botanical and economic aspects of the association Danthonietum calycinae have been thoroughly described in western Serbia -on Rajac, Maljen, Suvobor and Divčibare mountains and in the area of Sjenica (Cincović, Kojić, 1962). Dichanthium ischaemum (L.) Roberty is the dominant species of the community on Mt. Vidlič. This grass species tolerates livestock trampling, which makes it well-adapted to the prevailing pasture conditions. Its presence reduces harmful effects of erosion. Andropogono-Danthonietum calycinae plant community on Stara Planina (Mišić et al,197) and on Vidlič Mountain shows considerable similarities in its ecology and floristic composition with the аndropogonetosum ischaemi subassociation of Brometo-Chrysopogonetum grylli in Šumadija (Kojić, 1959). In Šumadija, Dichanthium ischaemum-covered surfaces have scented grass (Chrysopogon gryllus) in high abundance and cover, while it isn't the case on Stara Planina and Vidlič, where it occurs only in semi-open sites, with a stronger presence of Bromus squarrosus species. Figure 1 shows the localities where phytosociological plots of thermophilic meadows and rocky grounds were taken on Mt.Vidlič.
The resulting phytosociological table (Table 1) shows dry grasslands and rocky grounds of Mt. Vidlič, at the altitudes ranging from 480 to 1100 m, with S, SE and W exposures and the terrain inclination of 5-40°. The number of species and subspecies is 46-66 per plot and the value of Simpson diversity index is in the range between 0.976 and 0.985. Ten plots comprise a total of 242 species and subspecies. One single plot comprises 86 species and subspecies, indicating great diversity.
There are numerous species of steppe, sub-Mediterranean and Mediterranean character on dry grasslands and rocky grounds of Mt. Vidlič. Adamović (1899) and Soó (1951)  Phytosociological classification of dry grassland and rocky ground vegetation based on its floristic composition is shown in Graph 1. According to environmental conditions, which are more or less homogeneous, the majority of plots (1-2, 6-10) proved to be similar. These are plots at low altitudes (635m) ( Table 1), grouped in the right-hand part of Graph 1. They belong to the zone of oak forests. The central part of the graph comprises dry grasslands and rocky grounds in the zone of mesophilic forests, i.e. in the transitional zone between the oak and beech forests at an altitude of 635m (plots 7, 9, 8, 6, 10 and 3). Rocky grounds are especially notable in the zone of beech forests above 1000m a.s.l (plots 4 and 5). Altitude was the major factor in the classification of stands on rocky ground according to their similarity.
The largest number of species and in this respect the greatest diversity was found in plots 4 and 5 which are in the zone of beech forests, followed by the plots at somewhat lower altitudes in the transitional zone between the  Table 2). The smallest number of species i.e. the smallest diversity was found in plots 1 and 2, which are located at the lowest altitudes of Mt. Vidlič in the zone of degraded thermophilic oak forest with hornbeam (Quercetum frainetto-cerris subass. Carpinetosum orientalis). As seen in Figure 1 the stands located at higher altitudes (F) are segregated from all the other stands. The stands located at lower altitudes (A, B, C, D, E) make one group, although there is a clear distribution along the elevation gradients within the group.
The largest number of species and consequently the greatest diversity (Whitaker, 1972) was found in the dry grasslands and rocky grounds formed at the highest altitudes of Mt. Vidlič (above 1000 m), in the beech forest zone. They were followed by the plots at medium altitudes between the oak and beech forest belts. The smallest number of species and consequently the lowest diversity was found in the rocky ground vegetation at the lowest altitudes in the zone of hornbeam brushwood, which belongs to the zone of oak forests. In that sense, the diversity of the vegetation of open habitat types of the studied area increases with increasing altitude.

dIscussIon
It is a general fact that diversity of dry grasslands and rocky grounds correlates with altitude.
An increase in altitude increases vegetation diversity. According to Alard et al. (2005) the depth of soil and carbonate bedrock is in direct correlation with diversity, while soil fertility has direct effects on the stages of succession and species diversity. This fact can explain the highest level of vegetation diversity in the highest parts of the mountain, on eroded slopes with the increasing presence of chamaephytes. In their research studies, Fuhlendorf, Smiens (1998) point out that changes in soil conditions affect the dominance hierarchy between woody and herbaceous species. The density of herbaceous species may decline during succession with rival phanerophyte competitors (Brown, Archer, 1999). Better availability of nutrients at lower altitudes, which is related to soil depth and increased humidity, can explain the increasing number of shrub and woody plants compared to herbaceous individuals. This fact contributes to the decline in the index of diversity at lower altitudes.
Bearing in mind its marked steppe character, with the presence of numerous Pontic and sub-Mediterranean species, vegetation of dry grasslands and rocky grounds is important for several reasons. First of all, it has an important role in controlling erosion processes on steep slopes not only of Mt. Vidlič and in eastern and southeastern Serbia, but also in other parts of western Bulgaria, eastern Serbia and the central parts of the Balkan Peninsula.
Dry grasslands and rocky grounds of this region are characterized by high floristic diversity, with the presence of numerous endemic and rel- Table 2. Orographic data, total number of species and diversity by Whitaker (1972)  conclusIons Dry grasslands and rocky grounds of limestone terrain on Mt. Vidlič belong to Festucion valesiacae (class Festuco-Brometea) and Seslerion rigidae (class Festuco-Seslerietea) alliances. The largest areas under the specified type of vegetation occur on the south and southwest-facing slopes of the mountain, with shallow and dry soil. There are numerous species of steppe, sub-Mediterranean and Mediterranean distribution. Stand classification, which was carried out according to their floristic composition, showed that altitude was the major factor in grouping stands by similarity. The number of species i.e. diversity increases with an increasing altitude which is followed by an increase in the number (of endemic and relict steppe specimens. Dry grasslands and rocky grounds have an important role in the prevention of erosion processes. Due to its great diversity, this type of vegetation is used for livestock grazing.
In the absence of other sources of animal feed in the rural areas of the southern slopes, the described dry grasslands and rocky grounds of Mt. Vidlič are of outstanding economic importance for this region.
Based on these results, we can suggest that future studies of the structure, dynamics and diversity of dry grassland and rocky ground vegetation would be of great scientific and practical importance.
Ackowledgements: This research was conducted within the project of the Ministry of Education, Science and Technological Development of Republic of Serbia OI 171025, OI 173029 and TR 31070. We would like to express our sincere gratitude to dr Bojan Zlatković (Faculty of Sciences and mathematics, Niš) for his critical comments of the manuscript.