Article

First data on the adventive plants in Serbia date from XIX century, but the intensive studies begin in the lasl fifty years. At the beginning the records of new ad venti ve species were commented as one way of enriching flora. It was, however, noted that some species spread sub spontaneously, and rarely even spontaneously, but that was not considered very important. Today, when we know how important it is to preserve the natural diversity ofthe autochthonous flora and vegetation, the presence of the adventive plants must be considered to be a threatening factor. As a rule, these plants come from the remote biogeographic areas, -and in the new habitats have neither natura I enemies nor competition. They mostly have the low ecological requirements and the high level of ability to adjust. Some of these species spread very aggressively, especially in areas where the natural vegetation is disturbed or destroyed, and habitats devastated. By occupying that space, they disable the natural reversible processes of the autochthonous flora. After they enter the natural vegetation, they cause the relationship changes within communities, and lead to the serious disturbance ofthe natural succession. Factor ofthe introduction and further spreading of the adventive plants, both direct and indirect, is always anthropogenous. The urban and periurban areas, where the anthropogenous influence is most intensive and diverse, are the real "nurseries" ofthe adventive plants. From these habitats many species spread sub spontaneously, and some ofthem have already conquered habitats ofthe natural vegetation. It is unrealistic to expect total protection ofthe diversity of autochthonous flora and vegetation from the negative influence ofthe adventive plants. However, through use ofthe appropriate preventive and protective measures, the role of urban and periurban habitats in the appearing and spreading of the adventive plants could be significantly reduced.