SEGETAL FLORA OF THE MIDDLE VISTULA RIVER VALLEY

The objective of the study was to describe the segetal flora of the Middle Vistula River Valley. A total of 367 species were recorded in spring and winter cereals, tuber crops, and stubble fields. Such floristic abundance may be due to the fact that the study area is located in the proximity of a river where semi-natural communities interact directly with communities inhabiting cultivated fields and that fields are fragmented and characterised by different habitats. There were more apophytes (62%) than anthropophytes (38%) in the flora studied. Meadow apophytes were the dominant native species (35%) and archeophytes were the dominant anthropophytes (69%). The analysis of the life spectrum revealed that there were more therophytes (50%) than hemicryptophytes (39%). What is more, non-perennial species constituted 56% and perennials 44% of the segetal flora established in the Middle Vistula River Valley. The large proportion of archeophytes (26%) may indicate that traditional farming predominated in the study area.


INTRODUCTION
Soil and climatic conditions as well as anthropogenic factors affect the flora that establishes in cultivated fields.Changes in the floristic composition and structure of the communities have been observed for many years.Anthropogenic factors have the greatest influence on changes in segetal flora.They include the following: high mineral fertilisation, organic manuring, withdrawal of some plants from cultivation, the application of herbicides, reduced crop rotations, and the introduction of more efficient methods of seed material cleaning.Due to these factors, on the one hand, the area inhabited by specialised components of segetal flora is shrinking and some of them are even disappearing [1][2][3]; on the other hand, some species are increasing in number, their ranges are expanding, and they are penetrating new areas and habitats [4,5].
Studies on segetal flora have been conducted in Poland for a very long time.However, there are some regions where no such research has been attempted so far.The Middle Vistula River Valley is an example of such a region and W ó j c i k [6] is the only author who has reported some data for this area.

DESCRIPTION OF THE STUDY AREA
The Mesoregion of the Middle Vistula River Valley is located in east-central Poland.In physicogeographical terms, it has been classified by K o nd r a c k i [7] as a representative of the province of the Middle European Plain, sub-province of the Central Poland Lowlands, and macro-region of the Central Mazovian Lowland.
The Middle Vistula River Valley stretches from the Vistula gorge, runs through the Polish Uplands upstream of Puławy, and terminates at the valley's narrowing in Warsaw.The width of the valley is 10-12 km and its overall area is approximately 1350 km 2 .This section of the Vistula is around 120 km long; the river flows close to the left side of the valley and is quite wide (up to 1 km).According to Woś [8], the Middle Vistula River Valley belongs to two climatic regions: the Central Mazovian Region and the Eastern Lesser Poland Region.
The Middle Vistula River Valley has slightly worse climatic conditions than the adjacent areas.It is located low relative to the riverbed, which, coupled with shallow groundwater table, contributes to higher variations in daily temperatures.Also, air humidity is higher, winds are stronger, and fogs occur on 60 days per year.
The study area is located on two terraces.Fragments of oxbows with many temporarily or permanently flooded hollows are located on the first terrace, whereas the second terrace is composed mainly of sands with no water flows.
The persistence of groundwater depends on relative heights, geology and water level in the river.In the proximity of the valley, water is present at a depth of 3 to 5 m, whereas in the alluvial terrace groundwater occurs at a depth of 5 to 10 m.

MATERIALS AND METHODS
Fieldwork was carried out from 2003 to 2008 at 117 localities of the Middle Vistula River Valley (Fig. 1).Floristic and phytosociological observations were conducted in cereals, tuber crops, and stubble fields, using the widely approved Braun-Blanquet method; in addition, numerous floristic lists were compiled.The systematic layout follows R u t k o w s k i [9] and species names follow M i r e k et al. [10].A multifaceted analysis of the flora was performed taking into account the geographical and historical affiliation of species, their persistence, biological type and frequency of occurrence.It was based on the works by the following authors: R u t k o w s k i [9], Z a j ą c [11], J a c k o w i a k [12], K o r n i a k [13], and R o t h m a l e r [14].

RESULTS
The flora that accompanies cereals and tuber crops and grows in stubble fields in the Middle Vistula River Valley encompasses 367 species of vascular plants representing 45 botanic families and 201 genera (Table 1).The following families had the most species: Asteraceae, Poaceae, Fabaceae, Brassicaceae, Caryophyllaceae and Scrophulariaceae.Species of the most abundant families were mostly apophytes and anthropophytes, apart from Brassicaceae and Chenopodiaceae where anthropophytes dominated (Table 1).
The segetal flora in the Middle Vistula River Valley is very abundant.A total of 367 vascular species were found in cereals, tuber crops, and stubble fields.The flora in the study area seems to be much more abundant than in Mazovia [6], the Mazovian Landscape Park [22] or the Kampinos National Park [23].When compared with the rest of Poland, the study area has fewer species than the area of the Przeborsko-Małopolskie Range -393 species [24] and the Piotrków Plain -374 species [25].
Such floristic abundance was due to the fact that the study area is located along the banks of the Vistula River.A wide variety of habitats are found there, the dominant ones being fertile alluvial soils as well as acid and dry habitats.Also, the fields are fragmented and cultivated in quite a traditional way.
The analysis of the segetal flora demonstrated that apophytes were more numerous that anthropophytes.Such findings have been reported for other regions in Poland [6,13,22,[25][26][27].The opposite has been reported only for the Vistula delta area (Żuławy Wiślane) has [28].According to D ą b k o w s k a and S y g u l s k a [29], the fact that native species dominate over newcomers from different historical periods is indicative of a small effect of human pressure and slight transformation of segetal flora.Over 58% archeophytes of 165 taxons occurring in Poland [30] were found in the study area.Such a high share of this group of species in the flora of the Middle Vistula River Valley may be indicative of the dominance of traditional farming in the area.It has been reported in European literature that this group of species is receding due to the application of herbicides, the use of certified seeds for sowing, the abandonment of certain cultivation practices, the exclusion from cultivation of poor quality fields with infertile acid soils and oligotrophic carbonate-rich habitats, and changing the ways in which fields are used [2,17,31].Under Polish conditions, the fragmentation of fields may be an additional factor as it contributes to less competition with native species.In recent years, agrocenoses have also been effected by the increasing proportion of foreign invasive species which may threaten the native flora [32][33][34][35].The epecophytes that had a special influence on the composition and structure of communities in the study area included the following: Oxalis fontana, Veronica persica, Conyza canadensis, Galinsoga parviflora, and Anthoxanthum aristatum.

FloraFig. 2 .
Fig. 2. Percentage proportion of geographical and historical groups in the segetal flora of the mesoregion of the Middle Vistula River Valley.

Fig. 4 .
Fig. 4. Percentage proportion of individual groups of anthropophytes in the segetal flora of the Middle Vistula River Valley.

FloraFig. 5 .
Fig. 5. Percentage proportion of forms in the segetal flora of the Middle Vistula River Valley.

FloraFig. 6 .
Fig. 6.Percentage proportion life of species in the segetal flora of the Middle Vistula River Valley.