Seeds usually transported by air can be transported to unusually distant places through equally unusual transport methods - like getting sucked into the air intake of a refrigerated shipping container. A recent study that involved vacuum-cleaning air intake grilles of shipping containers at the Port of Savannah, Georgia, revealed the presence of these stowaway seeds.

A recent study was conducted by researchers from the United States Department of Agriculture (USDA) Forest Service, together with Arkansas State University and other organizations. The results of their findings are published in the journal Scientific Reports on September 14.

Identifying the Hitchhiking Seeds

In the introduction of the study, researchers noted the increase in biological invasions due to the increasing volume of economic trade, adding that these are often difficult to manage or contain from the receiving end.

The USDA Forest Service-led study focuses on "air-intake grilles of refrigerated shipping containers containing an agricultural commodity at the container terminal at the Port of Savannah, Georgia, USA." These shipping containers follow the route that starts from South America, then passes through the Panama Canal, staying for 16 to 72 hours, before continuing to the Port of Savannah.

During their first season of cleaning and collecting seeds, researchers were able to sample 5,537 seeds that were sorted into 27 morphotypes. In the following season, they sorted 5,509 seeds into 44 morphotypes, with common morphotypes between the two seasons totaling 59 unique morphotypes.

They then focused on the four most common monocotyledonous taxa: Saccharum spontaneum L(wild sugarcane), Typha sp(p) (cattail), Phragmites sp(p), and Andropogon sp(p). They then analyzed the odds of these seeds surviving and germinating in the United States. All four taxa were defined as prolific seed producers that survive on wind pollination and dispersal methods. Furthermore, these nonnative plants can survive in a wide range of environmental conditions.

Rima Lucardi, the lead author of the study from the USDA Forest Service, estimates that over 40,000 seeds of wild sugarcane entered the Garden City Terminal at the Port of Savannah. She added that the quantity of invading seeds is more than enough to establish the nonnative plant on US soil, even with precautions from shipping containers.

Strategies to Control Seed Invasion

The germination rates or viability of transported seeds can be of significant interest to federal regulatory and enforcement agencies. For example, the wild sugarcane is a grass listed under the US Department of Agriculture's Federal Noxious Weed List.

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The USDA list identifies plant species that pose "immediate, significant threats" to local agriculture, nursery, and forestry environments in the US. Despite its appearance, wild sugarcane can cause the same ecological effects as cogongrass, stiltgrass, and other nonnative invading species already widespread in the country.

Researchers propose several strategies to mitigate the adverse effects of these nonnative plant invasions. Aside from vacuum-cleaning air-intake grilles, which is described as a labor-intensive measure, port authorities can also administer liquid pre-emergent herbicides to minimize survival and germination rates.

"Investment in the prevention and early detection of nonnative plant species with known negative impacts results in nearly a 100-fold increase in economic return when compared to managing widespread nonnatives that can no longer be contained," Lucardi notes.

Check out more news and information on the USDA Forest Service on Science Times.