**1. Introduction**

We analyzed the sandy vegetation along the Danube in the central area of the Carpathian Basin, notably the calcareous sandy grasslands, which neighbor forest-steppe patches. The Pannonian–Pontic environmental zone (PAN) of the Carpathian basin, the Middle and Lower-Danube Plains and the Black-Sea. This area within characterized by natural forest-steppe and steppe vegetation [1–3]. The western borders of the Palaearctic steppe zone stretches across Eastern Europe, with high coverages of steppe and steppe-like grasslands in Bulgaria, Hungary, Moldova and Ukraine. The most important grassland types and subtypes in Eastern Europe [4] are the steppe grasslands (*Festuco-Brometea: Festucetalia valesiacae*), which are primary grasslands in the Eastern European region associated with the steppe and forest steppe zones. They are typically distributed in lowlands and at the foothills, and characterized by the dominance of *Festuca* and *Stipa* species.

The origin and history of the vegetation in the Pannonian zone are not always clear [5]. In the last centuries the original zonal appearance of the vegetation went through significant changes and became mosaic-like [6]. In the Carpathian Basin the zonal arrangemen<sup>t</sup> of the soil types and climate disbands completely, giving the place a mosaic-like landscape [6,7]. As a result, a mosaic-like vegetation types appeared. In areas with calcareous soil in the central area of the Carpathian Basin the environmental factors are also mosaic-like [8–10]. According to [11], in the sandy areas of the Danube-Tisza Interfluve, di fferent vegetation patches are formed along environmental gradients. These gradients can be physical parameters, such as soil moisture, soil structure, exposure or temperature [12–14].

According to [15], in natural forest steppe transitions, trees can have a major e ffect on herb vegetation composition. In the understory of the forest and grove patches the species composition is di fferent but instead of being a refuge of forest-specialized herbs other grassland-specialized species appear, contradicting the stress-gradient hypothesis [16,17], which states that competitive partners can change to facilitative ones at higher stress levels.

The regeneration potential of steppes is considerably lower than that of wet meadows, so mowing alone or intensive grazing is not e ffective in maintaining the diversity of the vegetation, though its more effective than abandoning it [18,19]; complex methods of low-level grazing and mowing should be used [20]. Ref. [21] also mention that richness of the soil can be a negative factor in the regeneration of arid steppes, since on more fertile soils the ruderal competitors make the natural recovery of specialist species nearly impossible.

According to [22,23], 45% of woody cover can be considered to be a threshold level, above which grassland specialist herbs give way to forest-related ones. They state that forest-steppe mosaics, closed forests and open grasslands also form a mosaic on higher altitudes, which also has to be taken into consideration when the managemen<sup>t</sup> and conversation of these complex habitats are planned.

Refs. [24,25] summed up the main features and characteristics of Eurasian forest-steppes in an extensive review in which they describe the highly diverse fine-scale grassland-forest mosaics in the Carpathian basin as forest-steppes with characteristic species (among others) such as *Quercus* spp., *Acer tataricum*, *Populus alba* and herbs like *Chrispopgon gryllus*, *Festuca vaginata*, *F. rupicola*, *F. valesiaca*, *Stipa* spp. and *Astragalus* spp.

In the past few centuries, significant changes occurred in the relationship of forests and grasslands between the Danube and the Tisza. Grasslands appeared to replace forests and some swamps disappeared [26,27]. In the

contact zones or rather, according to the present results, in places once covered in forests, open sandy surfaces formed then became inhabited by vegetation in a relatively short period of time [21,28–30]. At the same time, effects of human interventions can be detected long after they ended [31]. In places once covered in forests succession begins as a natural way of the regeneration of vegetation [32–36].

The soil-vegetation relationship in the sandy regions of the Danube–Tisza Interfluve was described and assessed by [37,38]. Ref. [39] also performed a botanical study of the Juniperetum of the Bugac area, in which he characterized the di fferent vegetation types, compiled flora descriptions supplemented with coenological data and provided a guideline for the evaluation of the location of the vegetation types of the Hungarian Great Plain. Járó [40] (1974) summarized the types of habitats of the Danube–Tisza Interfluve and described soils as an important factor in determining its development.

The close surface geology of the Danube–Tisza Interfluve region is determined by mainly carbonatic eolian sediments of the Danube River. Based on the grain size distribution of the parent material (from coarse, medium and fine sand to the silty loess) and the hydraulic conditions (particularly the depth and quality of the water table) di fferent soil types were developed in the area. At the high and dry landscape positions carbonatic shifting sands and humic sandy soils (Arenosols) can be found, which are characterized by unfavorable physical and chemical properties (high permeability and low water and nutrient storage capacity), thus they have low fertility [41,42].

Due to the regular redistribution of the eolian sandy deposits in the past buried soil horizons are quite frequent in the sandy soils of the region. The properties (i.e., grain size distribution, organic carbon content or the present soil structure) and the depth of the buried horizons may improve the fertility of the surface sandy soils and can provide information of the former soil forming environment as well [42]. The presence of soil structure or the di fferent colors at di fferent depths of the sands are also good indicators of former soil development under di fferent conditions and vegetation cover of the past [43,44].

The climate of the region is continental with a sub-Mediterranean influence. The annual precipitation is 500–600 mm (maximum in June) with a mean temperature of approximately 11 ◦C, and increasing aridity from north to south [45–47].

Ref. [48] separated several new series within the *F. ovina* group. *F. vaginata* and *F. pseudovaginata* belong to the *F. psammophila* series [49,50]. The other newly described series is *F. trachyphylla,* which *F. tomanii* belongs to, according to its morphological features [51].

We posed the following questions: (i) How does the present vegetation reflect the original, natural vegetation? (ii) Are there any proof that there were forests patches in the area? (iii) Could the present grassland vegetation be a hint of the forest-steppe character? (iv) What inferences can be drawn when paralleling the present state of the vegetation with soil data?

In order to answer these questions we analyzed the pedological background of the vegetation types and used the survey of [52], which is the longest examination of sandy grasslands in the Pannonian Region, being conducted after shrub cutting and a fforestation for 14 years continuously.

#### **2. Materials and Methods**

Coenological records were made in the central part of the Carpathian Basin, in 4 geographic units from northwest towards south and southeast. In the 4 areas dominant *Festuca* taxa were *Festuca vaginata, F. pseudovaginata* and *F. wagneri*, which were used as a baseline when di fferentiating records. The selected grasslands stretch along the Danube (Figure 1): 1. Little Hungarian Plain, Csallóköz; 2: northern part of the central area of the Carparthian Basin (Kiskunság); 3: southern part of the latter (Kiskunság) and 4: the southernmost sandy area of the Basin (Deliblát). Preferably, we chose sample areas on 3 di fferent plain in each vegetation type.

**Figure 1.** Location of the sample areas.

Taking this into account, our sample areas were the following:

*Festuca vaginata* grows everywhere along the Danube, and it appears in every studied geographic units. We could examine 3 sample areas in each northern part: the Little Hungarian Plain (I.1.Fv); northern part of Kiskunság (I.2.Fv) and southern part of Kiskunság (I.3.Fv). On the southernmost part (Deliblato, Serbia) only 1 sample area could be analyzed (I.4.Fv).

*Festuca pseudovaginata* grows only in the Carpathian Basin, on the northern plane. We examined 3 vegetation types dominated by it, based on the clearly visible physiognomical differences. The first one was a degraded type dominated by weeds at Vácrátót (II.1.Fp): The other one was more diverse, containing also arboreal species at Újpest (II.2.Fp): the third one was a natural grassland at Kunpeszér-Kunadacs (II.3.Fp).

*Festuca wagneri* was also found everywhere along the Danube in the Pannonian Region of the Carpathian Basin: in the Csallóköz (III.1.Fw), Northern part of Kiskunság (III.2.Fw), Southern part of Kiskunság (III.3.Fw) and in the southernmost part, at Deliblát (III.4.Fw).

The following relative ecological indicators [53] were used: relative temperature requirements (TB):



1: Plants with high drought tolerance often in areas that are completely dehydrated or persistently extremely dry (rocky, semi-desert);


Nitrogen requirements (NB).


Taxon nomenclature was used according to [54]. Association nomenclature was used according to [5]. Values of digesting extreme climatic conditions (continentality, KB) were also used based on the 9-level scale of [55], which was based on [56]:


Spatial heterogeneity of soil cover was investigated by the use of a Dutch auger soil sampler and 2 soil profiles were opened and described in order to characterize the soil types of the study area. Morphological descriptions and classification of soil profiles were made on site according to international standards [57,58]. Based on our survey of soil and vegetation cover, 3 sampling sites were selected. Composite soil samples from the depth of 0–15 and 15–30 cm were collected for laboratory analysis from each selected sites and soil parameters that might be connected to vegetation were determined. Soil pH was measured in 1:2.5 soil–water suspension and in 1 M KCl, CaCO3 was obtained by the Scheibler Calcimeter, salt concentration

was determined by measuring the electrical conductivity of saturated paste [59] and soil organic carbon content (%) was determined by the wet chemical oxidation method given by [60]. The Walkley and Black method [61] utilizes a specified volume of acidic dichromate solution reacting with a known quantity of soil in order to oxidize the organic carbon. The oxidation step is then followed by titration of the excess dichromate solution with ferrous sulfate, then the organic carbon content is calculated using the di fference between the total volume of dichromate added and the volume titrated after reaction.

For data analysis and presenting the results, the PAST [62,63] statistical software was used. For comparing the vegetation of the di fferent localities, multivariate hierarchic cluster analysis (UPGMA—unweighted pair-group average [64]) was conducted using Euclidean mean distance. In the present study the diversity of vegetation is particularly important, therefore after collecting, contracting the data based on vegetation types, they were also analyzed using <sup>R</sup>ény<sup>i</sup> diversity profiles [65].
