SEGETAL FLORA OF THE ŁUKÓW PLAIN

The aim of the study was to characterize and analyze the segetal flora of the Łuków Plain. The study was carried out from 2003 to 2006 in 182 towns and villages. Vascular flora of the arable fields in the area under study consists of 305 species belonging to 39 families and 168 genera. The analysed flora is characterised by the prevalence of native species (64.6%) over alien species (35.4%). Archaeophytes dominate among anthropophytes, whereas meadow species are the most frequent in the group of apophytes. Annuals and biennials show a slight prevalence over perennials. The analysis of the life-form categories shows the dominance of therophytes (52.8%) as well as a relatively high share of hemicryptophytes (34.4%) and geophytes (12.5%). In the analysed flora, rare and very rare species constitute a vast majority (61.7%), whereas the common and very common species reach 13.1%.


INTRODUCTION
Segetal flora of the Łuków Plain so far has not been the object of a complete study.Data on the occurrence of vascular plants in the area can be found in the papers by C i o s e k and S k r z y c z y ń s k a (1989), C i o s e k et al. (1997), C i o s e k and P i k u l s k i (1997), but these data mainly concern other kinds of vegetation.The geographical ranges of some Sub-Atlantic species, e.g.Arnoseris minima and Teesdalea nudicaulis, run across this region.They are considered rare and endangered plants in many regions of Poland and in Europe (F i j a ł k o w s k i and N y c z , 1998; U r b i s z et al. 1998; S i c i ń s k i , 1998; K u b a t and K a p l a n , 2001; P r a s s e et al. 2001; C h e ff i n g s and F a r r e l l , 2005; P i n k e et al. 2006).
The reason for their regression is an increase in the area of fallow lands, afforestation of poor soils and their high sensitivity to herbicides, and high fertilization level (F i j a ł k o w s k i , 1994; F i j a ł k o w s k i and N y c z , 1998; S i c i ń s k i , 1998).The Łuków Plain is a typically agricultural mezoregion of rather traditional farming methods.For this reason, the numerous occurrence of speirochoric species in segetal flora of the studied area was noted.
These features of the area as well as the lack of studies on the flora of arable fields inspired the author to undertake this study on the Łuków Plain area.The aim of the study was to investigate and analyse the flora of the Łuków Plain, with a special attention to speirochoric and Sub-Atlantic species.

THE AREA UNDER STUDY
The Łuków Plain covers an area of about 2600 km 2 and stretches from Adamów and Kock to the Bug River Valley between Terespol and Mielnik (K o nd r a c k i , 2002) over the territories of several districts: Łuków, Siedlce, Łosice, Radzyń, and Biała Podlaska Districts.According to the physiographic division, the area belongs to the macroregion of the South Podlachian Lowland, which is a part of the province of the Central Polish Lowlands.It is the furthest to the east area of the Central European Lowland.The land features are not significantly diversified.The areas of denudation plains, sometimes slightly undulating, prevail here.The sediments of the Central Polish glaciation, mainly of the Odra Stage, primarily clays and sands of the basal moraine, were mixed and diluted during periglacial processes related to transgression and regression of the glacier.Fluvioglacial sands lying on different sediment levels in some areas are visible on the surface in the form of sands and clays.Sand forms are usually mixed with dust fraction.In the river valleys and land hollows, contemporary sediments developed in the form of peat on the mineral base and boggy soil.Poor soils prevail in the studied area (class IVb -29% and V -29%), whereas the best soils are extremely rare.From the floristic point of view, the Łuków Plain is an area of great interest, which mainly results from the fact that the north-eastern range boundaries of many species, for instance Abies alba and Daphne cneorum, run through this area.

METHODS
The field studies were carried out from 2003 to 2006 in 182 towns and villages in 19 communes.The studied region is shown in Fig. 1.Lists of plant species and 815 phytosociological relevés made according to the Braun-Blanquet method in cereal and root crops as well as in stubble fields constituted the material for flora analysis.The studies were carried out in cultivated fields, excluding balks, roadsides, and fallow lands.Taxonomic differences, the biological spectrum and geohistorical structure of the flora, along with stability and frequency of occurrence of the species, are presented in the paper.The used taxonomy is according to R u t k o w s k i (1998) and species nomenclature follows M i r e k et al. (2002).In defining the features of the species, the following papers were used: A n i o ł -K w i a t k o w s k a (1974), K o r n a ś (1968,1977), K o r n i a k (1992), R u tk o w s k i (2007), S o w a and W a r c h o l i ń s k a (1987), Z a j ą c (1979), Z a j ą c and Z a j ą c (1975,1992), Z a j ą c et al. (1998).The frequency of occurrence of the taxa is given according to the pre-arranged formula stating that the number of stands is equal to the number of towns and villages, where the following categories: very rare, rare, quite rare, frequent, quite common and very common, occur in 1-3, 4-14, 15-36, 37-72, 73-109, 110-145 and 146-182 stands, respectively.

RESULTS
The segetal flora of the Łuków Plain consists of 305 species belonging to 39 botanical families and 168 genera.Over 70% of the taxa are in the ten families most abundant in species.The most numerously represented families are as follows: Asteraceae (51 species and 34 genera), Poaceae (33 species and 20 genera), Fabaceae (24 species and 6 genera), and Brassicaceae (22 species and 18 genera) (Table 1).

DISCUSSION
The segetal flora of the Łuków Plain is abundant and diverse.When it comes to the number of species, it is far above the florae of Żuławy Wiślane Region (H o ł d y ń s k i , 1991) and Wielkopolska Region (L a t o w s k i et al. 1979) or the area of arable lands of Bolimowska Primeval Forest (W a r c h o l i ń s k a , 1988) and others.However, the number of species recorded in the investigated area is slightly lower than in the segetal florae of the neighbouring mesoregions: considerably smaller than that of Podlaski Przełom Bugu -346 species (S k r z y c z y ń s k a and R z ym o w s k a , 2001), and similarly compared to the Siedlce Upland area -320 species (S k r z y c z y ń s k a , 1994).The floristic abundance of the area under study stems not only from its considerable size but also from the diversity of habitats, the patch-like system of small fields, and relatively traditional agriculture.The influence of similar factors on segetal florae has also been mentioned by: K o r n i a k (1992), S k r z y c z y ńs k a and R z y m o w s k a (2001), W a r c h o l i ńs k a (1991), and others.Most of the above-mentioned factors also result in the prevalence of apophytes over alien species.These correlations are confirmed by investigations from other regions of Poland (K o rn i a k , 1992; B o m a n o w s k a , 2006; W a r c h ol i ń s k a , 1991).The significance of the considerable contribution of light and acid soils in the Łuków Plain is also undeniable, as they make a favourable habitat for native species that occur here abundantly, especially those from sand habitats and dunes.The phenomenon of dominance of apophytes was observed in the Masovian Region by W ó j c i k (1968), who is of the opinion that in these habitats apophytes successfully compete with specialised, typical field weeds, particularly archaeophytes.
The extensive method of farming and habitat characteristics also influence the biological spectrum and stability of the species.The proportion of therophytes is slightly over 50%, with a substantial representation of hemicryptophytes and geophytes.The percentage structure of life-forms is similar to that observed in Podlachian Bug River Gap (S k r z y c z y ńs k a and R z y m o w s k a , 2001) and north-eastern Poland (K o r n i a k , 1992).S z o t k o w s k i (1989) explains the decreasing rate of hemicryptophytes by the effect of human activity defined as changes in agro-technology.A relatively small prevalence of annuals and biennials over perennials was observed in the investigated area.This fact indirectly stems from the dominance of apophytes and a considerable representation of hemicryptophytes and geophytes, which is caused by the same factors that contribute to the prevalence of apophytes over anthropophytes.

REFERENCES
A n i o ł -K w i a t k o w s k a J . , 1974. Flora

Fig. 1 .FloraFig. 2 .Fig. 3 .Fig. 4 .Fig. 5 .
Fig. 1.Location of the Łuków Plain against a background of physical-geographic division of Poland In the flora in question, the most numerously represented families are Asteraceae and Poaceae.The same tendency is observed not only in the segetal florae of different regions of Poland (R a t u s z n i a k and S o b i s z , 2006; S k r z y c z y ń s k a , 1994; B o m an o w s k a , 2006), but also in the florae of other European countries, both in the south and north of Europe (G l e m n i t z etal.2000).Sub-Atlantic species occur in the Łuków Plain with different frequency.Arnoseris minima is a frequent species; though, it is less frequent in the east of the mesoregion, whereas Teesdalea nudicaulis is a very rare species.Stands of the latter species in the area under study were recorded by C i o s e k and S k r z yc z y ń s k a (1989) and C i o s e k etal.(1997).The narrow ecological amplitude and the decrease in the area of poor, acidic habitats (afforestation, fields lying fallow) result in regression of these species.Another reason for their disappearance is the high fertilization level and use of herbicides.The above mentioned species are considered to be rare components of the flora that are threatened with extinction in many regions of Poland and in Europe (F i j a ł k o w s k i and N y c z , 1998; U r b i s z etal.1998; S i c i ń s k i , 1998; K ub a t and K a p l a n , 2001, P r a s s e etal.2001; C h e f f i n g s and F a r r e l l , 2005; P i n k e etal.2006).Anthoxanthum aristatum also belongs to rare species.When studying rare species in the South Podlachian Lowland, C i o s e k and S k r z y c z y ń s k a (1989) did not record stands of this species in the Łuków Plain.The characteristic feature of the investigated area is the occurrence of abundant populations of rare speirochoric species that are becoming extinct in Poland, such as Agrostemma githago, Bromus secalinus, and Avena strigosa.These species are in regression in Poland as a result of use of certified seed material (W a r c h o l i ń s k a , 1981, 2002; F r e y , 1989; Ż u k o w s k i and J a c k o w i a k , 1995; A n i o ł -K w i a t k o w s k a , 1998; S i c i ń s k i , 1998; N ow a k etal.2003).The persistence of these species in the agrocenoses of the Łuków Plain arises from traditional farming methods, particularly from the growers' use of their own badly-cleaned sowing material, which results from poor financial conditions of many farms in the region.The connection between rare speirochoric species and extensive agriculture has been mentioned by K o r n a ś(1972, 1987), H o ł d y ń s k i and W o ź n i a k (1994), H o c h ó ł (1990), and others.