China has undergone enormous economic growth in the last 25 years, largely as a result of greatly increased international trade. This burgeoning trade has triggered environmental threats from an expanding list of biological invaders: nonnative species previously unknown in China (e.g., the American vegetable leaf miner, the fall webworm) have arrived and are already causing damage to China's environment and economy. Huge construction projects, such as the Three Gorges Dam and the recently completed rail link to Tibet, could further spread invasive species to once-isolated portions of the country. The environmental risks from this onslaught are immense: China is one of the world's hotspots of biodiversity with about 30,000 native species of vascular plants and at least 2340 species of native terrestrial vertebrates. Fostering governmental and public awareness in China of the costs of invasive species and the multiple benefits of their prevention and control will be key to countering this menace.
Each nation receives and contributes to the worldwide pool of immigrant species through its international trade (Ruiz and Carlton 2003); some of these immigrants become invasive and wreak enormous damage in their new ranges (Mack et al. 2000). The list of species native to China that are now invasive elsewhere includes such well-known pests as the Asian long-horn beetle (Anoplophora glabripennis [Motschulsky]), the emerald ash borer (Agrilus planipennis [Fairmaire]), the multiflora rose (Rosa multiflora [Thunb.]) and white pine blister rust (Cronartium ribicola [J. C. Fisch.]). In turn, China has received alien species that have become naturalized and even invasive (tables 1, 2).
Dates of introduction and outbreak for 17 invasive plant species in China.
Dates of introduction and outbreak for 22 invasive animal species in China.
These invaders could be merely the forerunners of an onslaught into China. The rate at which introduced species arrive, including those that become invasive, is accelerating in step with China's surging economic growth since implementation of its landmark “Reform and Opening” policy in 1978. In the last 10 years, China has had the world's highest growth rate in gross domestic product (GDP), such that the total value of its imports and exports grew from US$20.6 billion in 1978 to a staggering US$1422.1 billion in 2005 (NBSC 2006). Such phenomenal growth in international trade portends environmental damage on a potentially huge scale, because the volume of a nation's international trade and the numbers of recently arriving invasive species form a strongly positive correlation (Levine and D'Antonio 2003).
The effects of an invasive species can be immediate, conspicuous, and profound. For example, Beijing, the host for the 2008 Summer Olympic Games, launched a concerted campaign in 2006 against the introduced fall webworm (Hyphantria cunea [Drury]), a recent invader from North America that has swiftly devastated Beijing's urban landscape by defoliating more than 200 plant species, including valued ornamental trees (Jia 2006). This introduced insect is however only one of more than 400 alien species now considered invasive in China (Xie et al. 2001).
Although all nations face a growing threat from biological invasions (di Castri 1989), the challenge for China in blocking these invaders' advance may be especially formidable. The growth of China's industrial and transportation infrastructures, including many mammoth construction projects, are facilitating introduced species' dispersal and establishment throughout the country, thereby setting the stage for potentially rampant environmental damage. For China, as well as for any other nation, both the causes and potential solutions of these pending environmental crises deserve enhanced research, public education, and governmental attention (Lodge et al. 2006).
Growth of transportation networks: Increasing pathways for invaders
As any nation opens its borders more to commerce, it automatically increases the opportunities for the entry of invasive species. A total of 253 airports, seaports, and railway and motorway stations in China—double the number in 1987 (CC 2007)—are now international ports of entry. China's exports and imports by seaports have risen from 311.5 million metric tons in 1985 to 2538 million metric tons in 2004 (Cui 2005), and potentially invasive species can be accidentally transported as hitchhikers in or on cargo containers, as well as deliberately transported (primarily plants and vertebrates). International travelers can also deliberately or accidentally introduce species that later prove to be invasive (Ruiz and Carlton 2003). Here again, the magnitude of this travel in China has increased enormously, to 16.93 million passengers in 2004 (NBSC 2006), almost triple the number in 1995. China's expanding domestic transportation networks almost certainly facilitate the spread of potentially invasive species across the country through myriad deliberate and accidental modes of transport (Ruiz and Carlton 2003). For example, the total length of express highways in China has grown from 1000 kilometers (km) in 1988 to 40,700 km in 2005 (NBSC 2006). These improved roadways serve an escalating number of the nation's civilian vehicles, which have increased to 26.93 million—a 20-fold increase since 1978. Simultaneously, the number of passengers on domestic flights was 138.27 million in 2005, compared with just 2.31 million in 1978 (NBSC 2006) (for other transportation changes, see figure 1). The transportation record in the last 25 to 30 years for Shanghai, China's largest commercial port, is emblematic of the greater facility with which nonnative species can move inland. The volume of domestic-bound freight transported from Shanghai via roads increased to 326.84 million tons in 2005 from 72.84 million tons in 1980 (SSB 2006); similar increases have occurred for freight carried by other modes of transportation (figure 2). Among such rapidly expanding systems of distribution, the opportunity for the accidental domestic transport of non-native species is substantial because the system of cross-provincial plant and animal quarantine and inspection is inadequate (Wang 200