The process of ecosystem fragmentation influences diversity and ecological stability in a significant way. This paper presents the results of analysis of changes in fragmentation and the ecological stability of the floodplain forest geobiocenosis in the Vrapač National Nature Reserve, a model area used for research into optimal forest reserve management methods in the Czech Republic (Simon, 2007). Using GIS methods, it was determined that fragmentation within this floodplain forest area decreased slightly between 1938 and 2006, and that the ecological stability of the landscape remains high. The results speak in favour of those theories advocating anthropogenic conditioning of floodplain forest ecosystems and show that even strongly anthropogenically modified geobiocenoses may show a high level of ecological stability, which is especially characteristic of the geobiocenoses of floodplain forests (Maděra, 2003).