Zurich

Abstract

Zurich, which is the largest city in Switzerland, is situated to the north of the Alps and at the northern end of Lake Zurich in an area with a rather cool sub-oceanic climate. More than 1,400 indigenous or naturalised species of higher plants have been recorded in the city, of which almost 200 (mainly archaeophytes) have become extinct within the last 160 years. The extinctions were caused by habitat loss resulting from the intensification of agricultural production and residential and other forms of development. On the other hand 300 new species have been able to colonize and become established in the city. The reasons for this being general climatic warming and the “heat-island effect” that is a characteristic of the urban environment. The previously relatively cool summers prevented many species from achieving their life cycle, which the recent warmer temperatures now allow them to. Also the milder winters enable many species to survive in the city, over winter, particularly in sheltered places. The absence of really cold winters for more than 20 years has enabled some sub-tropical plants to survive throughout the winter and even set fruit and regenerate from seeds, for example, the palm Trachycarpus fortunei.