Perspectives on general trends of plant invasions with special reference to alien weed flora of Shanghai

Abstract

Plant invasions are unintended consequences of globalisation, which facilitates the transglobal movement of plant species across all geographical and physical boundaries with the vastly increasing movement of people and commercial goods. As an internationalised city that has various channels through which plants′ movements occur, Shanghai has been subject to a heavy invasion of plants. This paper firstly deals with some characteristics of plant invasions in Shanghai. It is concluded that: 1) alien plants play an important role in the flora of Shanghai, accounting for 57.4% of the total flora; 2) annual and biennial plants are the major components of Shanghai′s alien flora, representing 69.1%; 3) most alien plants belong to a relatively few families (e.g. Asteraceae and Poaceae); 4) monocotylous families tend to have a higher proportion of alien plants with respect to their world′s number of species than do dicotylous families; and 5) plant invasions will continue to sweep across literally every part of Shanghai as the consequence of its further urbanisation and increasing global trade (c.f. China′s entry into WTO by November 2001). These patterns of plant invasions reflect the role of humans as global plant dispersers and of human disturbance in plant invasions. In the rest of the paper, we briefly review other issues in the field of plant invasions, including attributes of invasive species, habitat invisibility, environmental and economic costs of plant invasions, and future research directions.