The fragments of forest gene bases (FGBs) play an important role in gene pool preservation in Slovak lowland areas with changing hydrological regimes. A FGB fragment of gene base is defined as a complex of forest stands of autochthonous tree species in an intensively managed agricultural landscape. In spite of the fact that FGBs do not ensure full autoreproduction forest tree species in situ due to the limited sizes (5-50ha) they contain representative fragments of their regional populations. In the course of 1992 to 1997, we demarcated 19 FGB in the south of Slovakia of which 3 are situated on the alluvial sites of lower Morava river (22.61 ha), 6 of the Danube (108.9); 5 of Váh (11.86) and 3 of Hron (18.82) rivers and 2 are at East-Slovakian rivers (50.13). Tree willows and poplars occupy 33 per cent while almost 67 per cent of FGPs are hardwood riparian forests. In each fragment, the plus trees and registered seed stands of II-A or II-B category suitable for seed harvesting were selected. Obtained reproduction material has been cultivated in the nursery of the Forest Research Station Gabčíkovo and on field research plots.