CONCLUSIONS This contribution includes the results of four-years of research of the epigean Heteroptera in floodplain forests (assoc. Salici - Populetum) in the region of the Gabcikovo project. Bugs were collected during 1991-1994 at eight monitoring sites using square method. Collected 947 individuals belong to 59 species and 10 families. Evaluation of Heteroptera taxocoenoses was based on their quantitative representation as expressed by the average abundance values per 1 m2, taking into account the qualitative structure with emphasis to the constancy and dominance values and according to determined characteristic species and individuals.The occurrence of epigean Heteroptera is not equally distributed at individual study sites and during the year. The occurrence of Heteroptera is influenced by natural and also antropogenic factors. The decrease of the average abundance and the increase of species diversity, caused by a long-lasting drought in 1993 and by changes in the hydrological regime and following ruderalisation, was only a temporary phenomenon.

INTRODUCTION

From this aspect we have used the following main criteria for the evaluation of the epigean Heteroptera taxocoenose structures:

1. Quantitative representation expressed by the average abundance values to an area of 1 m².
2. Qualitative composition expressed by species with accent on their constancy and dominance.
3. The relation of the biotope to the species with regard to the occurrence of species, which are characteristic for floodplain forest biotopes and which are possible, from the aspect of fidelity, to evaluate as eucoennic elements.

METHODS The research of epigean Heteroptera took place at eight monitoring areas (MA) within the forest community of Salici - Populetum during the years 1991 to 1994. The basic data (number, name, locality and year of research) is presented in Tab.1. Tab. 1. Monitoring areas - basic data

Indication	Name	Locality	Observation period
MA No. 1	Ostrov Kopáč	Podunajské Biskupice	1991-1994
MA No. 3	Ostrovné lúčky	Čunovo	1993-1994
MA No. 6	Dunajské kriviny	Dobrohoš	1991-1994
MA No. 9	Bodícka brána	Bodíky	1991-1994
MA No. 10	Krá3/4ovská lúka	Trstená na Ostrove	1991-1994
MA No. 14	Istragov	Gabčíkovo	1991-1994
MA No. 18	Sporná Siho	K3/4účovec	1991-1994
MA No. 23	Starý les	Číčov	1993-1994

Material of Heteroptera was collected by sifting. At each MA 16 squares of material samples containing leaf litter and the upper part of the soil, each of an area 25x25 cm, was collected, at 3-4 week intervals from April till October. The numbers of occurring individuals are expressed in values of the average abundance to an area of 1 m². Some species obtained by individual sifting of the soil, individual sampling and collection using the method of earth traps were used for the evaluation of the qualitative structure of Heteroptera.

RESULTS

The average abundance of bugs in individual years reached the following values: 1991 - 5.88 ex.m^-2, 1992 - 5.78 ex.m^-2, 1993 - 3.94 ex.m^-2 and in 1994 - 4.19 ex.m^-2. On the basis of quantitative representation of Heteroptera in each individual MA it is possible to place them into three categories. The highest values of the average abundance were recorded at MA No. 6 - 7.35 ex.m^-2 and No. 9 - 9.53 ex.m^-2, average ones at MA No. 1 - 5.60 ex.m^-2, No. 18 - 4.38 ex.m^-2, No. 23 - 5.00 ex.m^-2 and the lowest ones at MA No. 3 - 2.16 ex.m^-2, No. 10 - 1.16 ex.m^-2 and No. 14 - 2.67 ex.m^-2.

To estimate the reason for such variable quantitative distribution of bugs at individual MA's, we recorded the values of their average abundance in individual years, separately for each MA. The decrease of the quantitative representation of epigean Heteroptera was manifested in the whole territory in 1993 (except for MA No. 14). After the subtraction of individuals from MA No. 3 and 23, where there in 1991 and 1992 research was not realised, up to about 42 % less individuals occurred in 1993 than in 1991 and about 33 % individuals less than in 1992. It was shown, that the synergism of the influence of natural and anthropogenous factors and long-lasting drought and changes of the hydrological regime was manifested negatively in the decrease of the population density of more hygrophilous bug species, and a decisive decrease in their quantitative representation in 1993. Results from 1994 show, that this state was not irreversible, because in areas, mainly MA No. 6, 9 and 10, which are situated in the influenced territory, the values of the average abundance of epigean bugs again increased.

Evaluation of the qualitative structure of Heteroptera taxocoenoses show that in the first two years of research the numbers of ascertained species were nearly the same (1991 - 30 spp., 1992 - 29 spp.), in 1993 the number of species decisively increased (42 spp.) and in 1994 again decreased (26 spp.). The increase of epigean bug species in 1993 was connected with changes in the hydrological regime in the floodplain forests, with a decrease in soil moisture, but also with the ruderalisation of vegetation and other, probably climatic impact. The consequence of these facts, even if in isolated numbers of individuals, there occured more meso- to xerophilous species of Heteroptera in the epigaean of floodplain forest. For example the species Metopoplax origani, Graptopeltus lynceus, Xantochilus quadratus, Peritrechus geniculatus and some others, occurred only in our collections in 1993, (Tab 2.).

Apart from the situation in 1993, the species spectrum of epigean Heteroptera taxocoenoses of floodplain forest is possible to characterise by a low degree of homogeneity, which was manifested by a high number of accidental and accessory species. These occurred in number 44 spp., which is 74.58% of all species found. There were 11 (18.64 %) constant species and only 4 species (6.78%) were euconstant. There are more reasons for such heterogeneity of the qualitative structure of epigean Heteroptera taxocoenoses. First of all it is necessary to stress that floodplain forests of the association Salici - Populetum have a different character on individual monitoring areas, which is not only influenced by present human activities. Jurko (1958) stated, that within the frame of the association Salici - Populetum in this territory, there are four variants; according to the depth of the groundwater, the depth and duration of floods and the relief configuration, from the most humid places to the driest ones (relatively). The driest variant occurs at MA No. 1 and 3, where the floodplain forest is situated close to the Danubian forest steppe (Crataegetum danubiale). More xerothermophilous species have penetrated to the forest community from this area and this mainly in spring and later in summer and autumn, in connection with hibernation. Only in such a way it is possible to explain the occurrence of such stenoecious species as for example Ceraleptus gracilicornis, C. lividus, Coptosoma scutellatum, Thyreocoris scarabaeoides, Odontoscelis fuliginosa and Dyroderes umbraculatus in the floodplain forest. A lot of them are rare in the Slovak territory and till now they were only found in xerothermophilous biotopes.

Apart from the above-mentioned species, occurring only at MA No. 1 and 3, we also recorded at the other monitoring areas more epigean species, which are not typical for biota of floodplain forest and are known as species of settled xerothermophilous biotopes with calcarious or sandy substrate. Some of them occurred only sporadically and created accidental and accessory elements, as for example Stygnocoris sabulosus, Rhyparochromus phoeniceus, Megalonotus sabulicola, Emblethis griseus and Trapezonotus arenarius. Some other species were recorded at the majority of MA's and in every year of the research. From the aspect of constancy there are constant species (Emblethis denticolis, E. verbascii, Arenocoris falleni) and euconstant ones (Eremocoris podagricus and Meganolotus chiragra), but from the aspect of dominance they are always only of subrecendent to recendent species. An occurrence of these species is obviously interconnected with the presence of alluvial plant communities, which exist in floodplain forests on sandy or gravel-sandy soils. In times of long-lasting drought these small populations have suitable conditions. All presented species, but also some other sporadically occurring species, create a group of accompanying or occasionally occurring species in the taxocoenose of epigean Heteroptera of floodplain forests.

During the research into the relationship of biotopes special attention has been devoted to species, which are characteristic for floodplain forest and from the aspect of fidelity, represent eucoennic elements in the epigean Heteroptera community. Of such species, indicated first of all hygrophilous ones, which occupy leaf litter and soil surface, but also hygrophilous herbicola and arboricola, which occur in leaf litter at a certain period of the post-embryonic development. So the following characteristic species were recognized: Aradus distinctus, Cymus claviculus, Holcocranum saturejae, Drymus brunneus, D. ryeii, Scolopostethus affinis, S. thomsonii, S. pictus, Legnotus limbosus and Podops inuncta. Some of them occurred in our collections only sporadically (Aradus distinctus, Cymus claviculus, Holcocranum saturejae, Scolopostethus pilosus, Podops inuncta), but other species were recorded regularly at more monitoring areas. The majority of them created dominant and subdominant elements in the taxocoenose of epigean Heteroptera. The share of the characteristic species in the quantitative distribution of bugs was for the whole territory during individual years of research as follows: in 1991 - 82.90%, in 1992 - 83.68%, in 1993 - 60.15% and in 1994 - 70.82%. Given data confirms, that the population of characteristic species have a dominant position in epigean Heteroptera community and they create an important part of the epigeon of floodplain forests. The percentage distribution ratio of characteristic species is shown in Fig. 2., where their prevalence is visible at MA No. 23, but even in other areas (except MA No. 3) was the quantitative distribution of characteristic species high (44 to 88%) (number of characteristic species increased from 15% to 39%). In order to present the differences in individual areas, a percentage distribution of characteristic species and their individuals are shown separately for every year of research in Table 2. The quantitative-qualitative distribution of characteristic species was the lowest at MA No. 1 and 3, the highest at Ma No. 23 and high values were recorded in 1991 and 1992 at MA No. 18 and in 1992 at MA No. 9.

The population of an eudominant Drymus brunneus has the main share of the high quantitative distribution of characteristic species, which is a typical element of litter in humid forests, where it feeds on the sap of mosses and fungi [5]. This species is possible to characterise as an indicator of a sufficient humidity of floodplain forests and its presence or absence has in this sense a sufficient significant value. The dominance of imagoes and nymphs of Drymus brunneus in individual years of research reached the following values: in 1991 - 59.58%, in 1992 - 62.34%, in 1993 - 32.92% and in 1994 -40.20%. If we compare the percentage values of the characteristic species quantitative representation and the values of the dominance of Drymus brunneus, we find that in both cases a decrease happened in 1993. This can be interconnected with the influence of negative natural and anthropogenous factors, and a decrease in the groundwater level in the spring of 1993. Results, attained in 1994, allow us to state that in comparison with the previous year it is possible to observe in more areas a certain degree of revitalisation, the consequence of which, despite a long-lasting drought, the structure of the epigean Heteroptera has stabilised in the observed territory.

DISCUSSION AND CONCLUSIONS

On the basis of data obtained from four-years of research it is possible to state that the results of the epigean Heteroptera study have a bioindicating validity, at judging the degree of preservation of the natural environment in forest communities, as observed in gradual time-step of eventual changes. The structure of the epigean bug taxocoenoses is influenced by natural factors, mainly humid conditions of substrate which are influenced by the groundwater level, surface floods, long-lasting drought etc., and by anthropogenous factors - the cutting of forests and the devastation of the terrain with following desiccation of the soil substrate, the ruderalization of vegetation and other negative phenomena. It follows from our results, that in the majority of monitoring areas, which represent a relatively preserved type of floodplain forest, the structure of the epigean Heteroptera taxocoenoses is influenced mainly by natural factors, the consequence of which it arose some differences in species composition and representation of characteristic species in various areas.

The impact of anthropogenous factors, which were negatively manifested mainly in 1993, can be indicated as temporary. We can state this fact on the basis of our results reached in 1994, that the structure of the epigean bug taxocoenoses has gradually stabilised in more areas and begins to returns to the state of 1991.

Acknowledgement

REFERENCES

[1] Jurko, A., 1958: Soil-ecological conditions and forest communities of the Danubian lowland (in Slovak). SAV Bratislava, 264 pp.

[2] Puckov, V., 1969: Lygaeidae (in Ukrainean). Fauna of Ukraine, 21, Kyjev, 388 pp.

[3] Stehlik, J. L., Vavřinova , I., 1993: Results of the investigations on Heteroptera in Slovakia made by the Moravian Museum (Pentatomoidea II.). Acta Mus. Moraviae, Sci. nat., 77, p. 157-208.

[4] Stepanovicova, O., 1994: Heteroptera-Pentatomomorpha of characteristic habitats in the Moravian floodplain area. Ekológia (Bratislava), Suppl. 1, p. 163-174.

[5] Wagner, E., 1966: Wanzen oder Heteroptera I. Pentatomorpha. Die Tierwelt Deutschlands, 54, 235 pp.

C-constancy
As-accessoric species
*-not ascertained specie by quadrate method
EK-euconstant species
Ad-accidental species
K-constant species
N-no research