Development of vegetation in localities of pedunculate oak dieback in Croatia.
Dieback of pedunculate oak (Quercus robur) forests in lowland Croatia is currently an important forestry problem. The dieback is due to a synergistic interaction of various adverse factors, and has resulted in the enforced logging of some 600 000 m3 of stemwood on 20 000 ha of the most badly affected areas in the NW of the country over the last thirty years. Dieback has been most severe in the forest association of pedunculate oak and Genisto elata (Genisto elatae-Quercetum roboris). In most locations, this association was developing towards an oak/hornbeam (Carpinus betulus) forest association (Carpino betuli-Quercetum roboris). Forest vegetation changes due to oak dieback have led not only to the disappearance of pedunculate oak, but also many species of the well-structured phytocoenosis, and has also resulted in the expansion of some pioneer herbaceous species. Among the latter, those growing on more humid, waterlogged and open (degraded) sites are particularly prominent, e.g., Amorpha fruticosa, Bidens tripartita, Filipendula ulmaria, Carex riparia, Myosotis scorpioides, Galium palustre, Peucedanum palustre, Juncus effusus, Polygonum hydropiper, Lythrum salicaria, Carex elata.