Invasive Plant News

A recent article reviews trees and shrubs around the world that are considered invasive.  The article summarizes an exhaustive review of regional and national databases and literature.  Some of the important woody invasives are the twenty-one woody plant species featured on the widely cited list of “100 of the World’s Worst Invaders” (Lowe et al., 2000).The article concludes that only between 0.5% and 0.7% of the world’s tree and shrub species are currently invasive outside their natural range, but the importance of woody plant invasions is rapidly increasing.

The article is free.  The authors are David M. Richardson and Marcel Rejma´nek.  Here is the link: Trees and shrubs as invasive alien species – a global review.

Road graders may spread the seeds of invasive plants. Researchers at Penn Staten looked at Japanese stiltgrass. Left alone, the plant spreads only a few feet a year, but foresters in Rothrock State Forest in Pennsylvania saw much more rapid advances. The researchers used colored seeds (heated to prevent sprouting) to track movement of seeds next to rural gravel roads. The reseachers found that the seeds could move as far as 250 meters in two years. Here is a longer article on the research in Science Daily.

Why are some invasive species so successful in their new environments?  A group of researchers recently examined invasive velvetgrass, Holcus lanatus and its effect on the seaside daisy, Erigeron glaucus. Rather than looking at single mechanisms, the researchers looked at multiple.  They studied direct competition, changes to the soil community, indirect competition from  changes in herbivore feeding, and interference competition due to allelopathy (i.e., biochemicals produced to affect the growth, survival, and reproduction of other organisms).  The study found that direct competition had the strongest effect but that changes to the soil community continued to harm native species even after the removal of the velvetgrass.

The authors are Dr. Alison Bennett and Dr. Sharon Strauss at the University of California Davis, and Dr. Meredith Thomsen at the University of Wisoconsin, La Crosse.  The findings are published in the American Journal of Botany.