Floristic composition as an indicator of destabilisation of lowland forest ecosystems in Posavina

Background and Purpose: The succession of forests in the Posavina region follows a pattern from forests of black alder and ash through stands of pedunculate oak to pedunculate oak-hornbeam forests. In the past hundred years, this lowland area has been affected by a number of factors, among which anthropogenic influences hold a primary position. This has resulted in a considerable deviation from normal, natural succession. The purpose of this paper is to analyse the present condition, the degree of destabilisation and the future developmental trends of pedunculate oak stands by drawing on previous pedological, hydrological and vegetational research. One of the best indicators of the above is the ecoindicator values of the floristic composition. Materials and Methods: Phytocoenological relevés were taken in 25 localities of both stable and destabilised forest ecosystems of pedunculate oak in Žutica Forest. The principles of the Zurich-Montpellier School were applied for this process. The numerical analysis was carried out by means of SYN-TAX 2000 software. JUICE 6.3 and CANOCO 4.5 were also used to process the relevés, construct the phytocoenological tables and correlate species compositions and vegetation typeswith ecological factors. The obtained results were compared with the results of earlier ecological research. Results: Phytocoenological research revealed significant changes in the floristic composition. Ecoindicator values of plant species indicate a substantial change in ecological parameters and increased destabilisation, which leads to larger quantities of light, thermophilicity and humidity in sites. In addition, the sites are richer in nitrogen and the soil reaction becomes more basophilic, while central European species replace intermediary ones. Conclusions: The investigated plots show a regression process contrary to the normal direction of vegetation development in lowland areas. A return has been observed from the final community to transitional comm