A recent study led by scientists at UC Santa Barbara’s National Center for Ecological Analysis and Synthesis demonstrated how globalization and the demand for drought-resistant plant species threaten to overcome native plants in the United States. Based on these findings, the scientists proposed that bio-imports be screened before entering the U.S.

The paper, co-authored by UCSB environmental studies professor Carla D’Antonio, was published in the online edition of Frontiers in Ecology and the Environment.

According to D’Antonio, human interference with dams, roads, pollution and agriculture can create environmental changes for native plants and give exotic ones an ecological advantage.

“The places that an exotic plant species dominates have been altered by a disturbance or some kind of environmental stress usually induced by humans,” D’Antonio said.

In Santa Barbara, coastal sage scrub habitats are particularly susceptible, as are wild grasslands, which have a tendency to catch on fire during drier months, allowing non-native species such as Mediterranean grasses and mustards to invade.

As a result, scientists involved in the research have encouraged the U.S. Dept. of Agriculture to implement preemptive management practices like those adopted in Florida, Hawaii and Australia, where non-native species ravaged the environment. The suggested rule, “Not Authorized Pending Pest Risk Analysis,” would require travelers and international businesses to alert the USDA about possible exotic imports. This law would allow scientists at the USDA to perform controlled experiments in order to study how foreign plants interact with native species.

Frank Davis, director of NCEAS and professor at UCSB’s Bren School, explained the philosophy behind the screening process.

“The lesson from past experiences is that the best way to reduce the impact of nuisance exotic species is to prevent their introduction in the first place, or at least manage them deliberately to reduce the risk of spread,” Davis said in an email. “To do this takes help from the horticultural industry and increased public awareness.”

While as much as 40 percent of non-native species were introduced accidentally by humans, nearly 60 percent of invasive plants owe their success to gardeners looking for more drought-resistant plants in the face of increasing temperatures. According to the study, “Climate change is likely to increase demand for drought- and heat-tolerant landscaping plants in the U.S. Emerging trade partners have warm, dry climates that are well matched to this future demand and could supply many new and potentially invasive species.”

However, the problem is twofold, according to Deputy Director of NCEAS Stephanie Hampton, since exotic plants may grow better than native plants in some areas.

“As climate changes, it alters not only the environment that non-native species encounter, but also society’s demand for exotic imports,” Hampton said.

In addition to plants, insects and pathogens also pose a threat to certain plants native to California. For example, pathogens from Asia have killed oak trees, especially in northern California. As international trade increases, opportunities for non-native plant and insect infestation also arise, which remains a major concern among environmental scientists.