The Berlin area was formed during the Quaternary and is mostly covered with Weichselian and Holocene sediments. The primeval vegetation, as reconstructed by pollen analysis, soil conditions, historical reports and recent vegetation patterns, has totally changed due to the large city development since the second part of the 19th century. Today about 3.5 million people are living in the city of Berlin on 889 sq km. To understand the relationship between the plant species and the environment, it is necessary to see the present flora and biotopes as a result of the historic development. Plants can exercise a positive influence on both the climate and the air in the surroundings. Through transpiration, humidity is increased (it is often too dry in towns), and the heat required for evaporation avoids excess temperatures. Thus green areas can help to produce cool air, which is a necessary compensation in highly built-up areas. In addition, plants in vegetation belts help, to some extent, to absorb noise. Arguments for the conservation of wild plants in the cities also lead to some remarks concerning nature conservation practices in Berlin.