A CONTRIBUTION TO STUDIES OF THE RUDERAL VEGETATION OF SOUTHERN SREM, SERBIA

Floristic research investigating the presence and phytocoenological differentiation of ruderal vegetation, and how it is conditioned structurally and anthropogenically, was undertaken over a period of several years (2007-10) in the south Srem region. The ruderal flora of the research area comprised 249 plants categorized into 63 families, of which the most frequent were: Asteraceae (36), Poaceae (29), Fabaceae (18), Lamiaceae (15), Polygonaceae (15), Brassicaceae (11) and Rosaceae (11). Three ruderal communities are analyzed in this work: Asclepietum syriacae Kojić et al., 2004, as well as Chenopodio-Ambrosietum artemisiifoliae ass. nova and Amorpho-Typhaetum ass. nova, which are described for the first time. It was established that the level of moisture at the habitat, anthropogenic factors, and the immediate proximity to cultivated areas had the most pronounced effect on the differentiation of the researched vegetation.


IntrODuctIOn
ruderal vegetation represents a highly dynamic floristic/vegetational complex, which develops most often in human settlements, but also in other environments which are permanently or temporarily exposed to anthropogenic influences.Anthropogenic factors are of key significance in the formation, survival, distribution, diversity and dynamics of this type of vegetation.The specificity and diversity of ruderal habitats are conditioned by their location.
In this work, three communities are analyzed: Asclepietum syriacae ass.nova Kojić, 2004, developed on raised flood defense levees and in expan-sive meadows, Chenopodio-Ambrosietum artemisiifoliae ass.nova in abandoned fields and along roadsides, and Amorpho Typhaetum ass.nova in the zone of drainage canals.the aim of this research is to establish: the floristic composition of the associations found; the abundance and cover of species; the phytocoenological differentiation of the associations into appropriate syntaxa; life forms; floral elements; syntaxonomic elements; the impact of ecological factors on the differentiation of ruderal vegetation; and the presence of non-native plants.

MAterIAl AnD MetHODS
The research area (between the village of Boljevci and the Forest estate Management unit 'Progarska ada -crni lug -Zidine -Drenska') lies in the borough of Surčin and is situated 72-74 m above sea level (Fig. 1).relevés of the described communities were marked on the flood defense levee, in meadows, in abandoned fields, along roadsides, and in the zone of drainage canals.
During the analytical phase of the research, the qualitative and quantitative composition of the plants in each relevé was established.The recorded plant species were established on the basis of several literary sources (Josifović, 1970(Josifović, -1980;;Javorka and chapody, 1975;tutin, 1964-1980;Aichele and golte-Bechtle, 1997;grey-Wilson and Blamey, 1979), and their abundance in the analyzed relevés was determined by the Westhoff and van der Maarel combined abundance/cover scale, which is an entirely numerical method and, as such, is completely applicable in the mathematical processing of data (Westhoff and van der Maarel, 1973).During the synthetic phase of research, which was based on the association table method (Müller-Dombois and ellenberg, 1975;gauch, 1982), groups of those relevés most similar in terms of flora were selected.The software package 'FlOrA' was used for rearranging the phytocoenological tables (Karadžić et al., 1998).literary sources were used to establish life forms (raunkiaer, 1934;Stevanović, 1992) and floral elements (gajić, 1984;Stevanović, 1992a), as well as the connection be-tween the recorded plant species and the corresponding syntaxonomic units (ellenberg, 1979;Kojić et al., 1997Kojić et al., , 1998)).The correlation between environmental factors and the ruderal communities described was established by using canonical correlation analysis ccA (ter Brak, 1986(ter Brak, , 1988(ter Brak, , 1994)).

reSultS AnD DIScuSSIOn
The phytocoenological tables which show the floristic composition and differentiation into lower syntaxonomic categories (subassociations and facies) of the newly-described communities Chenopodio-Ambrosietum artemisiifoliae ass.nova and ass.Amorpho-Typhaetum ass.nova, as well as ass.Asclepietum syriacae Kojić et al., 2004, can be obtained from the authors via email: nena2000@ibiss.bg.ac.rs The ruderal habitats where this research was undertaken can be grouped into three categories in relation to the complex of anthropologic influences, as the key to the development of this vegetation type: trampled ruderal areas, untrodden ruderal areas, and wet, hydrophilic ruderal areas (Jovanović, 1994).The ruderal flora of the research area comprised 249 plants categorized into 63 families, the most frequent of which were: Asteraceae (36), Poaceae (29), Fabaceae (18), Lamiaceae (15), Polygonaceae (15), Brassicaceae (11) and Rosaceae (11).

Ass. Asclepietum syriacae Kojić et al., 2004
The association Asclepietum syriacae was found at the flood defense levee and in meadows and was differentiated into subass.stellarietosum (at the levee) and vicietosum sativae (in the meadows), Appendix 1. Moisture is the basic ecological factor leading to its differentiation, and in the syntaxonomic spectrum hygromesophytic species of the vegetation class Molinio-Arrhenatheretea predominate.

Structural characteristics
The ass.Asclepietum syriacae was determined on the basis of 11 phytocoenological relevés and is a graminoid ruderal community.Within the research area, it colonizes places which have been covered with soil, such as the levee, but also meadow areas which directly adjoin the levee.This association comprises 142 plant species, 131 of which are present in the composition of two or more relevés (92.3%).The ediphicator of the community is the non-native plant Asclepias syriaca and the typical set includes 49 (34.5%) more species.The species with the highest frequency are quite uniformly present in all relevés, which points to the existence of a relatively homogenous set of plants.The following species were recorded in all the relevés of the ass.Asclepietum syriacae: Galium mollugo, Alopecurus pratensis, Poa palustris, Cirsium arvense, Rumex palustris, Silene vulgaris, Holcus lanatus and Trifolium pratense.In addition to these species, other species characterized by high abundance are: Rubus caesius, Bromus mollis, Arrhenatherum elatius, Achillea millefolium, Plantago lanceolata, Medicago lupulina, Potentilla reptans and Dactylis glomerata.characteristic species are of great diagnostic importance because they give the association a specific appearance through their habitus, while their high levels of abundance and cover point to the stability of coenotic relations.twenty species from the family Poaceae also contribute to the physiognomy of the ass.Asclepietum syriacae.Among them are 10 from the group of characteristic species, which gives it a special quality.This is also the fundamental reason why the areas on which these stands have developed are mown from time to time, so as to use the existing biomass for fodder or bedding for animals.In addition, the other xenobionts of the association also have a direct influence on its structural/coenotic and physiognomic characteristics.

Ass. Chenopodio-Ambrosietum artemisiifoliae ass. nova
The association Chenopodio-Ambrosietum artemisiifoliae ass.nova was recorded along the edge of roads and in abandoned fields; it was differentiated into the subass.bidentetosum and rubetosum caesiae, as well as the facies lepidiosum.(v, Iv), the species mentioned are also characterized by high levels of abundance and cover, all of which conditions the specific physiognomy of this association on whose formation and survival anthropogenic factors (mowing, treading, etc.) have the greatest influence.

Ass. Amorpho-Typhaetum ass. nova
The association Amorpho-Typhaetum ass.nova was recorded at the habitats of the drainage canals, including the canals themselves, their banks, and the areas around the banks.It is differentiated into facies: typhosum, butomosum and sambucosum, and almost all ecological factors have virtually the same impact on its differentiation, as these are completely open habitats where the only fluctuating variables during the year are the water levels in the canals or the degree of moisture in the riparian areas.The syntaxonomic spectrum is dominated by hygromesophytic species of the vegetation class Molinio-Arrhenatheretea tx.1937.

Structural characteristics
The association Amorpho-Typhaetum was established on the basis of 10 phytocoenological relevés and is rich and varied in terms of flora: it comprises 178 plant species, 136 (76.4%) of which are present in the composition of two or more releves, Appendix 3. The ediphicators of the association are the nonnative species Amorpha fruticosa and Typha latifolia.A typical set comprises 38 species (21.35%), and in each of the stands of the association, besides the characteristic species Amorpha fruticosa, the follow-ing were also noted: Stenactis annua, Lolium perenne, Lythrum salicaria, Mentha aquatica, Bidens tripartitus and Calystegia sepium.The high presence of the species in the typical set and their high abundance and cover is an indicator of the stable coenotic relations of the fully formed association Amorpho-Typhaetum.A significant feature of the community is the presence of aquatic species in the drainage canals, and their abundance is a direct result of ecological factors, above all water level, the amount of nitrogen, and water temperature.

Biological spectrum
The biological spectrum of the vegetation of the recorded ruderal associations in the southern Srem region is hemicryptophytic in character and the most common hemicryptophytes are: Galega officinalis, Cichorium intybus, Plantago major, Plantago lanceolata, Ranunculus repens, and Lythrum salicaria (Fig. 2).
The high proportion of hemicryptophytes is in keeping with the dominant presence of this life form in the flora of Serbia, which, according to turrill and raunkiaer, makes the climate of this region, as well as that of the whole temperate Zone, 'hemicryptophytic' (Diklić, 1984).A particular characteristic of the biological spectrum of the researched vegetation is the presence of therophytes, which is directly connected to the instability of the majority of ruderal habitats where man hinders the development of plants (particularly perennials) through his activities, thus removing time as an ecological factor.As a rule, the less the impact of anthropogenic factors on a particular ruderal habitat, the lower the percentage of therophytes and the greater the proportion of biennial and perennial plant species in the composition of the biological spectrum (Kojić, et al., 1997).The most invasive therophyte in the research area is Ambrosia artemisiifolia.Thero-hemicryptophytes also constitute a high proportion of the biological spectrum of the described associations.The most frequent of these are: Daucus carota, Dipsacus laciniatus, Dipsacus sylvester, Erigeron canadensis, Stenactis annua and Pastinaca sativa.In terms of the total number of representatives, the geophyte life-form category is the second most numerous in the ass.Amorpho-Typhaetum and has a great influence on the physiognomy of the association, where hygro-helophyte geophytes (Alisma plantago-aquatica, Butomus umbelatus, Iris pseudacorus, Sparganium ramosum, Typha angustifolia and Typha latifolia) are especially prominent.The most frequent geophytes in the ass.Asclepietum syriacae and Chenopodio-Ambrosietum artemisiifoliae are: Asclepias syriaca, Cirsium arvense, Calystegia sepium, Convolvulus arvensis and Sorghum halepense.In terms of quality and quantity, the presence of phanerophytes in the identified associations is not high; most often they are present sporadically along roadsides and in the riparian zone of the drainage canals.A significant feature of the ass.Amorpho-Typhaetum is the presence of aquatic helohydrophytes (4.5%): amphibian and floating hydrophytes (Salvinia natans, Trapa natans, Nymphoides flava, Lemna minor, Lemna trisulca and Hydrocharis morsus-ranae) and submerged hydrophytes (Ceratophyllum submersum and Potamogeton fluitans).The percentage of the other life forms (dc, np, pl, zc) is low in terms of presence, occurring only sporadically in the stands of the research area.

Phytogeographic analysis
A phytogeographic analysis of the ruderal vegetation of the associations Asclepietum syriacae, Chenopodio-Ambrosietum artemisiifoliae and Amorpho -Typhaetum in the research area shows the high diversity of floral elements (25), as well as the domination of geoelements of wide distribution (evr., Subevr., Subse.) (Fig. 3).habitats, which are not stable enough in terms of coenology and competitiveness, and are mainly open, sunny, thermophilic, hygrophilically unstable habitats, and as a rule nitrophilous (Jovanović, 1994).The adventitive area type, a conditional chorological category, is represented by 22 species and is third in terms of total presence in the spectrum of floral elements, while the following cosmopolites are prominent in terms of their quantitative presence: Convolvulus arvensis, Polygonum aviculare, Typha latifolia, and Verbena officinalis.Among the circum-Holarctic species (cirk, Subcirk.), the majority are hydrophytes and hygrophytes, which only serves to confirm the fact that water environments lead to the equalization of ecological conditions on a wider geographical plan (Polygonum lapathifolium, Polygonum hydropiper, Stachys palustris, Typha angustifolia, Juncus articulatus, Juncus conglomeratus).The presence of other geoelements (primarily Subj.Sib., Subm.and Subpont.-subm.), as well as the entire biological spectrum is a direct result of the geographic position of the research area, which is situated on the main belt for the spread of Mediterranean ruderal species from the eastern Mediterranean towards europe on the one hand, and from central europe and the Pannonian Basin on the other.

Syntaxonomic spectrum
The associations Asclepietum syriacae and Amorpho-Typhaetum are dominated by hygromesophytic syntaxa represented by the class Molinio-Arrhenatheretea, while the ass.Chenopodio-Ambrosietum artemisiifoliae is dominated by syntaxa of segetal weed communities of crops and small grains represented by the class Stellarietea mediae (Fig. 4).
The similarity between ruderal and segetal vegetation is also shown by the presence of the vegetation class chenopodietea, within which the association Chenopodio-Ambrosietum artemisiifoliae exists.The high presence of segetal species in ruderal habitats is The spectrum of syntaxonomic affiliation of the ruderal vegetation in the identified phytocoenoses is a reflection of the ecological conditions of the habitat itself, the influence of surrounding vegetation, and the impact of anthropogenic factors.

Ecological differentiation of ruderal vegetation
The results of the ccA show that moisture plays the key role in the differentiation of ruderal vegetation (Fig. 5).
temperature has a somewhat lesser, but nonetheless important influence on differentiating these associations.Due to the mosaic layout and complete openness of those habitats where the moisture is greatest, in a great number of cases the temperature is also highest, and vice versa.
The remaining ecological factors (soil pH, light, and the nitrogen content of the habitat) have similar values, and hence the habitats of ass.Amorpho-Typhaetum ass.nova are the most nitrophyllic, acidic and heliophyllic, which is to be entirely expected as these are 'open' habitats.
The ruderal flora and vegetation of the research area has a number of similarities with that of Belgrade (Jovanović, 1994), Pančevački rit (Stanković-Kalezić, 2007) and eastern Srem (Kojić et al., 2004).Similarities can be seen in the following areas: in the large number of common species, because it is the same type of vegetation; in the domination of species from the family Asteraceae; in the greatest presence of hemicryptophytic and therophytic life forms; in the high presence of floral elements of wide distribution (evr., Subevr., Subse., Submed., cirk., Kosm.and Adv.); and the presence of a significant number of non-native plant species.The ass.Asclepietum syriaca Kojić et al., 2004 has been described in eastern Srem, close to new Belgrade and Zemun, in abandoned fields, along roadsides and in the areas between cultivated fields, as well as on the slopes of the flood defense levees along the river Sava, and it is floristically similar [ISs=38%] to the association with the same name found in the southern Srem region, because it colonizes similar habitats (the slopes of levees and expansive meadows).
The ruderal flora and vegetation of the research area, unlike that found in the urban part of Belgrade, is characterized by a significant presence of segetal plants, which is the result of it being in the immediate vicinity of agrophytocoenoses.However, the reverse process is also pronounced -the invasion of ruderal plants into cultivated areas.edaphic conditions and strong anthropogenic pressure, with elements of a land cultivation system and the application of suitable measures for weed control in cultivated areas, have an indirect influence on the development and survival of this type of vegetation.Moisture as an  Appendix 3. continued and Trifolium pretense.These species have the main influence on the physiognomy of the analyzed types of ruderal habitats, which is confirmed by the presence of the corresponding syntaxonomic elements, above all of the predominant vegetation classes Molinio-Arrhenatheretea and Stellarietea mediae.
The significant presence of non-native plant species ( 22) contributes to the study of the biodiversity of the research area: 14 in ass.Asclepietum syriacae, 16 in ass.Amorpho-Typhaetum ass.nova, and as many as 21 non-native species in ass.Chenopodio-Ambrosietum artemisiifoliae ass.nova.neophytes predominate in the chronological spectrum (15), and in terms of invasivity status, invasive plant species are dominant (11) (trinajstić, 1977).The presence of non-native species in the research area is above all the result of continual or temporary anthropogenic intervention which hinders the development of perennial plants and encourages the presence of annuals which prefer open habitats with favorable temperature and light regimes.
The ruderal vegetation of the south Srem region is characterized by a great diversity of plant species, distinctive dynamics, microfragmentation in distribution and the high morphoanatomic variability of its xenobionts.Studying this type of vegetation is not only important from the floristic and phytocoenological aspects, but it is also of great significance for direct plant production, because it is from these ruderal habitats that many species of weed invade cultivated areas and create great competition for crops.

Fig 1 .
Fig 1. geographical position of investigated area