ECOLOGICAL AND FLORISTIC CHARACTERISTICS OF THE NEW SUBASSOCIATION ACERI HELDREICHII-FAGETUM SUBASS. CARPINETOSUM BETULI ON MT. RUDNIK

Ecological and floristic characteristics of the new subassociation of the Balkan beech and Greek maple plant community with hornbeam (Aceri heldreichii-Fagetum subass. carpinetosum betuli) were studied. This subassociation is recorded and described on Mt. Rudnik, where it occurs at the elevations 9501,050 m, on moderate to steep inclinations (10-30°), and cold aspects: northern, northwestern and northeastern. Bedrock consists of sandstones and mudstones. The biological spectrum, ecological spectra and spectrum of distribution types of this community were calculated. The community has phanerophyte–hemicryptophyte character, it is mesophilous regarding soil moisture requirements and temperature requirements, it is neutrophilous to soil acidity, according to light requirements it is tolerant to semi-tolerant. The most numerous group of distribution types is Central European, which confirms the mesophilous character of this community.


INTRODUCTION
Greek maple (Acer heldreichii Orph.) is an endemic tree species of the Balkan Peninsula. It is distributed in Serbia, Montenegro, Bosnia and Herzegovina, FYR Macedonia, Bulgaria, Greece and Albania. It grows only in mountain zones, in Serbia it occurs at the elevation span of 1,000-2,000 m, but mostly between 1,200-1,800 m. Among native species of genus Acer L., Greek maple is the most adapted to cold climate. It could be found on all aspects, but mostly on northern ones, on milder slopes and in moist valleys, with deeper, more humid soils, with a prolonged snow cover (L a k u š i ć , 1964).
On Mt. Rudnik, Greek maple was first recorded by Gajić in 1955, on one part of the peak Mali Šturac, at the elevation of 950 m. He initially found only one deformed tree, 3 m high (G a j i ć , 1955). Later on, he found a group of Greek maple trees at this locality. G a j i ć (1959,1961) concluded that Greek maple grew on the mountain beech site.
Greek maple in Serbia grows as a dominant species in plant communities, almost exclusively in association with Balkan beech (Fagus moesiaca (Domin, Maly) Czeczott) (To m i ć , 2004). The plant community of beech and Balkan maple in Serbia was first described by Jovanović on Mt. Goč (J o v a n o v i ć , 1957) and it was named Aceri heldreichii-Fagetum.
The highest abundance of Greek maple is in the belt of subalpine beech forests, where it forms, alone or with subalpine beech, endemic communities of the Balkan Peninsula: Aceri heldreichii-Fagetum B. Jov. 1957in central Serbia, Aceri heldreihii-Fagetum subalpinum Jank. et Stef. 1983in Kosovo and Metohija, Aceri visianii-Fagetum Fuk. et Stef. 1958in Bosnia and Herzegovina, Fago-Aceretum visianii Bleč. et Lkšć. 1970in Montenegro (To m i ć , 2004. The plant community Aceri heldreichii-Fagetum subass. carpinetosum betuli is recorded on Mt. Rudnik and it represents a new subassociation of Greek maple and Balkan beech, with hornbeam (Carpinus betulus L.) as a differential species (Pe r o v i ć , C v j e t i ć a n i n , 2009). The site on Mt. Rudnik is the northernmost site of Greek maple in the world, and at the same time it is the site where Balkan beech and Greek maple community grows at the lowest elevations in Serbia. This research includes the analysis of ecological and floristic characteristics of this community.

MATERIAL AND METHODS
Five phytocoenological records were taken on Mt. Rudnik in the plant community of Balkan beech and Greek maple using the standard Braun-Blanquet method. The analysed elements were: floristic composition, biological spectrum, spectra of ecological characteristics according to K o j i ć , Po p o v i ć , K a r a d ž i ć (1997), as well as the spectrum of distribution types according to G a j i ć (1980,1984). Climatic data were given on the basis of the data of the meteorological station Rudnik, for the period 1965-2004. The Thornthwaite's index, Lang's rain factor, De Marton's drought quotient, and Kerner's quotient were calculated (Pe r o v i ć , 2007) based on the above data.

Study area
Mountain Rudnik is located in the central part of Serbia, in Šumadija region. The highest summit is Cvijićev Vrh (Veliki Šturac) at 1,132 m a.s.l. Mt. Rudnik stretches in various directions. To the east, south, southeast and northwest, this massif is clearly defined, while to the west and north its border is unclear and it descends in various lower hills. This massif is rich in streams and brooks, but most of them get dry during summer in the lower courses. The streams which do not get dry are: Despotovica, Jasenica and Gruža (G a j i ć , 1981).
Balkan beech-Greek maple plant community (Aceri heldreichii-Fagetum subass. carpinetosum betuli) on Rudnik is researched in the area of the peaks Mali Šturac and Srednji Šturac. The stands grow at the elevation of 950-1,050 m, the aspect is northern, northwestern and northeastern, and the inclination is moderate to steep (10-30 °). Greek maple trees are averagely 19-24 m high, with the diameter of 24-30 cm (1996).

Climatic data
Climatic data are given on the basis of the data of the Rudnik meteorological station (700 m above sea level) for the period 1965-2004. Mean annual temperature is 9.4°C, Greek maple on Mt. Rudnik Слика 1. Заједница балканске букве и планинског јавора на Руднику  the warmest month is August with the mean temperature 18.7°C, and the coldest month is January, with the mean temperature -0.6°C. Average temperature in the growing season is 15.2°C. The absolute maximal temperature in this period is 36.0°C, and the absolute minimum -18.2°C. Annual precipitation is 939 mm; the rainiest month is June with 131 mm, and the driest month is February with 55 mm. During the growing season, there is averagely 558 mm of precipitation. Annual relative air humidity is 76.5%; relative air humidity is the highest in January (84%), and the lowest in May and August (72%).
The value of Lang's rain factor is 100, which characterizes humid climate, represented with high forests. The value of Kerner's quotient of climate continentality is 9.8%, which represents the transition from mildly continental to littoral climate, which is in accordance with general climatic conditions of our mountain areas, where this quotient varies between 6% and 12% (K o l i ć , 1988). De Marton's drought quotient is 48.4 which shows that this is a typical forest region. Thornthwaite's index is 50.5 which indicates the intensified humid climate (B3) (Pe r o v i ć , M. 2007).

Geological characteristics
The bedrock of Mt. Rudnik is composed mostly of flysch sediments. Sediments of the golt-Cenomanian and the Senonian are also represented, as well as the sediments of the Hauterivian ⁄ Barremian, Barremian-Aptian, ugonic, sandstone-chert, Tertiary, etc. The most abundant sedimentary rocks are sandstones, marls, conglomerates, mudstones and diabases. Apart from sedimentary rocks, there are also volcanic rocks, mostly daciteandesite (A n đ e l k o v i ć , 1957).
On the basis of the collected rock samples from the researched area, it was ascertained that the community of Balkan beech and Greek maple on Mt. Rudnik grew on sandstone and mudstone bedrock (Pe r o v i ć , 2007).

Phytocoenological characteristics
Five phytocoenological releves were sampled aiming at the identification of phytocoenological characteristics. On the basis of floristic composition, it is ascertained that Greek maple forms a plant community with Balkan beech and hornbeam which is named Aceri heldreichii-Fagetum subass. carpinetosum betuli. That is a new subassociation of the association of Greek maple and Balkan beech in Serbia. The total number of 21 species is recorded in phytocoenological releves.
The canopy cover in the tree layer is 0.7-0.8, average heights are 11-20 m, average diameters 20-45 cm, average distance between trees is 3-6 m. Apart from Balkan beech and Greek maple, the following tree species are present in this layer: hornbeam (Carpinus betulus L), Sycamore maple (Acer pseudoplatanus L), Norway maple (Acer platanoides L.) and Small-leaved lime (Tilia cordata Miller).
The canopy cover in the shrub layer is 0.1 to 0.3, average heights are 2-5 m. The dominant species in this layer is Balkan beech (Fagus moesiaca (Domin, Maly) Czeczott). In addition, Black elder (Sambucus nigra L.) and Hazelnut (Corylus avellana L.) are also found.
The coverage of grass layer is 0.6 to 1.0. Apart from the regeneration of the tree and shrub species, another 13 species were identified. The most widespread is Raspberry (Rubus hirtus Walds. et Kit), which was registered in all phytocoenological records and which has the highest abundance and coverage. Apart from raspberry, the presence of Common male-fern (Dryopteris filix mas L. (Schott)) was also high.
According to soil moisture requirements, the community is mesophilous, because sub-mesophytes comprise 81% and typical mesophytes 19% of all plant species.
According to the requirements to soil acidity, community is neutrophilous, because neutrophilous species account for 86% of all species, neutrophilous-basophilous 10%, and acidophilous 5%.
According to soil nitrogen requirements, mesotrophic species account for 76%, mesotrophic-eutrophic 10%, oligotrophic-mesotrophic 10%, and eutrophic 5%, so it can be concluded that community has moderate requirements to soil nitrogen.
According to light requirements, tolerant-semitolerant species are the most numerous species (62% of the total number), semitolerant (29%), typical tolerant (10%), so the community has tolerant to semitolerant character.
The most important in the spectrum of distribution types is the Subcentraleuropean distribution type (29% of all species), then Central-European (19%), cosmopolitan (14%), Moesic and circumpolar (10% each), while Pontic-Eastsubmediterranean, Sub-Eurasian, Eurasian and Central-Balkan comprise 5% each. The most numerous group is that of Central-European distribution types (Central-European and Subcentraleuropan) with 48% of all species, then cosmopolitan and Submediterranean (Moesic and Central-Balkan) with 14% each, circumpolar and Eurasian (Eurasian and Subeurasian) with 10% each, and Pontic-Centralasian with 5%. It can be concluded that plant species of mesophilous character have the highest occurrence (Central-European group of distribution types) with 48%, then the species of broad ecological amplitude (Eurasian and cosmopolitan group of distribution types) with 24%, xero-thermophilous species (Submediterranean and Pontic groups of distribution types) with 19%, and, finally, plants of northern areas (circumpolar group of distribution types) with 10%.

DISCUSSION
Greek maple (Acer heldreichii Orph.) is an endemic tree species of the Balkan Peninsula. In its range it grows exclusively in mountain zone, in Serbia its elevation span is 1,000-2,000 m, but mostly between 1,200-1,800 m. According to L a k u š i ć (1989), mean annual temperatures on its sites are between 2 and 7°C, mean relative humidity is between 65% and 80%, absolute minimal temperatures drop to -35°C (-40°C), and absolute maximal temperatures rise to 30°C. Greek maple can be found on all exposures, but mostly on northern, on milder slopes and valleys with prolonged snow cover (L a k u š i ć , 1964). Among native species of genus Acer L., Greek maple is the best adapted to cold climate. Above the subalpine beech belt, Greek maple can be found in the form of low shrubs in the community of Blueberry (Vaccinium myrtillus L.) and Mountain juniper (Juniperus sibirica Burgsd.) which indicates its vitality and resistance to low temperatures (L a k u š i ć , 1964).
In the area of the former Yugoslavia, Greek maple grows as the dominant species in plant communities, almost exclusively with subalpine beech. The following communities are described: Aceri heldreichii -Fagetum B. Jov. 1957in central Serbia, Aceri heldreihii-Fagetum subalpinum Jank. et Stef. 1983in Kosovo and Metohija, Aceri visianii-Fagetum Fuk. et Stef. 1958in Bosnia and Herzegovina, and Fago-Aceretum visianii Bleč. et Lkšć. 1970. in Montenegro (To m i ć , 2004. Greek maple is among the best species for the differentiation of the subalpine from montane beech forests (M i š i ć , 1997). Very rarely it forms plant communities with Spruce (Picea abies (L.) Karst.) (S t e f a n o v i ć , 1970).
The association Aceri heldreichii-Fagetum subass. carpinetosum betuli described on Mt. Rudnik is the Greek maple -Balkan beech community recorded at the lowest elevations (950-1,050 m) in Serbia, and at the same time it is the northernmost Greek maple site in the world. Mean annual temperature measured in the meteorological station Rudnik (elevation 700 m, period 1965-2004.) is 9.4°C, which indicates that the stands of Greek maple and beech on Mt. Rudnik grow in a somewhat warmer climate than it is usual for this community. Relative air humidity (76.5%) is within the average values for this community. The absolute maximal temperature is 36°C, and the absolute minimum -18°C, which is significantly above the lowest temperatures recorded at Greek maple sites (-40°C) (L a k u š i ć , 1989). Such climatic conditions influence the floristic composition of Greek maple-Balkan beech community on Mt. Rudnik, which resulted in the higher occurrence of typical mesophilous species which do not grow in frigoriphilous conditions of typical Greek maple-Balkan beech stands. First of all, it is connected with the occurrence of hornbeam (Carpinus betulus L.) which is a differential species of this sub-community. The dominance of Central-European group of distribution types, the dominance of mesophilous species according to temperature and soil moisture requirements, and the phanerophyte-hemicryptophyte character of the community biological spectrum also indicate the typical mesophilous character of this plant community.

CONCLUSION
A new subassociation of the association of Greek maple and Balkan beech (Aceri heldreichii-Fagetum subass. carpinetosum betuli) is described on Mt. Rudnik, at the localities Mali Šturac and Srednji Šturac. This community grows at the elevation of 950-1,050 m, on cold aspects: northern, northwestern and northeastern. Inclination is moderate to steep (10-30°). This is the lowest elevation in Serbia at which Greek maple and Balkan beech community grows and, at the same time, the northernmost site of Greek maple in the world.
The climate is warmer than in the typical stands of Greek maple and Balkan beech.
The bedrock is composed of sandstones and mudstones. According to biological spectrum, the community is phanerophytic-hemicryptophytic, according to moisture requirements, the community is mesophilous, according to soil acidity -it is neutrophilous, according to soil nitrogen content -mesotrophic, according to the light -tolerant to semitolerant, according to temperature requirements -mesophilous.
As for the spectrum of distribution types, the most numerous is the group of Central-European distribution types. The most important floristic difference of this plant subassociation from the typical Aceri heldreichii-Fagetum B. Jov. 1957 association is the presence of typical mesophilous species, hornbeam (Carpinus betulus L), which is a differential species of this sub-community. The dominance of Central-European group of distribution types, the dominance of mesophilous species regarding the temperature and soil moisture requirements, and the phanerophyte-hemicryptophyte character of the community biological spectrum also indicate the typical mesophilous character of this plant community.