Yoshiko Shimono1, Mafumi Ikeda1, Takeshi Nishi1, Motoaki Asai2 and Tohru Tominaga1
1Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
2Tohoku Agricultural Research Center, NARO, 50, Harajikuminami, Arai, Fukushima, 960-2156, Japan
e-mail: email@example.com (Yoshiko Shimono)
International trade of grain commodities is a major pathway for the unintentional introduction of alien plants because the seeds of various weed species contaminate grain commodities. These seeds spill out of grain commodities during unloading, transportation and usage, and some of them are naturalized in grain-importing countries. Although propagule pressure (the number of individuals arriving at a new location and the number of arriving events) is considered one of the most important driver of invasion success, little is known about the effects of weed seed contaminants on local vegetation at their introduction sites. Therefore, we analysed the relationship between the quantity of weed seeds included in grain commodities and their establishments at international trading ports which are primary introduction sites for the contaminating weed seeds.
We conducted vegetation surveys at 21 international trading ports in Japan, including 11 ‘grain importing ports (GIPs)’ and 10 ‘non-grain importing ports (NGIPs)’. We also investigated weed seed compositions in grain commodities imported into Japan and a contamination percentage was calculated for each species based on our survey and previous studies on weed seed contaminants.
Vegetations at GIPs were clearly different from those at NGIPs. More alien species established at GIPs than at NGIPs. An indicator species analysis showed that more than 20 species belonging to the family Poaceae, Brassicaceae, Amaranthaceae, and Convolvulaceae were characteristic of GIP vegetation. These species showed high contamination percentages. On the other hand, only seven species were characteristic of NGIP vegetation and these species were not detected from grain commodities. Our study revealed that invasion of alien species through weed seed contaminants in grain commodities strongly affects local vegetation at international trading ports.