With their species diversity, their population abundance and their integrator characters, higher plants represent useful tools to solve problems concerning the environment analysis and management. As they are good bioindicators, plants integrate many environmental parameters and can help to reveal the misworking of the ecosystems. Within this framework, a recent and complete survey of the phanerogamic flora of the Brussels area was carried out by the method of the floristic grid-map based on 1 km - squares. A comparison with earlier data has allowed us to appreciate the consequences of half a century of human activities on plant diversity in the urban ecosystem. The basic aim is to present a method of diagnosis and mapping that has been used, so as to turn the descriptive information about the biological environment of the area into a series of guidelines for land-use regulation and management within the city. Ellenberg's indicator values were used to express the relationship of flora to soil nitrogen, moisture content, reaction, light and temperature. Considering the biological characteristics of new floristic components and plants which have become rare or disappeared, it was possible to draw conclusions about the alterations in environmental conditions in Brussels. Our results show that the number of species did not differ significantly from 1940 until now. However, considerable changes have appeared during this period: there is a clear increase in the number of alien species; the flora of the Brussels area is becoming more nitrophilous and tolerant to shade, while it does not differ with respect to soil moisture, reaction and temperature. Human activities have disturbed the distribution and abundance of many species, inducing a decline or disappearance Of some of them, principally those which are associated with cropland, with marshland and woodland. On the other hand, numerous species have recently appeared in the city, many of which are aliens. The comparison between indigenous and alien species has revealed that their occurrence depends upon their ecological requirements: alien species are more tolerant of nitrogen, light, drought, heat and alkaline soils. The response of the flora to human impact is clearly demonstrated. Such sensitivity has obvious implications for both conservation and management. Circumstances, where Brussels plant monitoring is carried out permitting the avoidance of potential disaster and the saving of valuable biological resources, are developed. Arguments for the conservation of wild plants in cities also lead to some remarks concerning nature conservation practices in Brussels. © 2001 Elsevier Science B.V.
