Time bombs: Invasive plants can lie dormant for centuries

In a new study from UC Davis, researchers have discovered that invasive plant species can lie dormant for extended periods – spanning decades to centuries – before abruptly proliferating and causing significant ecological damage. 

The experts scrutinized over 5,700 invasive plant species across nine global regions, marking it as the most exhaustive study of its kind, according to senior author Mohsen Mesgaran, an assistant professor in the Department of Plant Sciences at UC Davis.

Invasive time bombs 

Mesgaran highlighted the deceptive nature of these dormant phases: “The longer it is dormant, we’re more likely to ignore it. This latency allows them to be overlooked, contributing to their eventual emergence as a serious invasive threat. They’re like invasive time bombs.”

The study’s findings reveal that about one-third of the analyzed invasive plants underwent a significant lag between their introduction and sudden expansion, with an average dormancy period of 40 years. 

Dormant invasive plants

The record for the longest dormancy was held by sycamore maples in the United Kingdom, clocking in at 320 years. 

In the United States, the common lawn weed Plantago lanceolata, also known as ribwort or buckhorn plantain, boasts the longest dormancy period. Introduced in 1822, this plant, detrimental to livestock and native flora, is now widespread across the country. 

Another plant, velvetleaf, introduced as a potential fiber crop, can remain dormant for 50 years before spreading and threatening vital crops like corn and soybeans by depleting water and nutrients.

More problems ahead

The experts argue that non-native species introductions occur either accidentally or through deliberate importation for uses such as medicinal, ornamental, or agricultural purposes. In California alone, approximately 65% of invasive plants were introduced intentionally. 

“This lag phase may have played a role,” Mesgaran said. “They didn’t know. With an increase in trade and transportation and tourism we’re going to have more problems.”

Waiting for favorable conditions 

To compile their data, the researchers drew from global herbarium records, which are digitized and publicly accessible, to track the occurrence and timeline of these invasive species across various regions, including Australia, Great Britain, Ireland, Japan, New Zealand, Madagascar, South Africa, and the United States. 

By analyzing these records and comparing climate conditions during dormant versus expansion phases, the team discovered that many species waited for or adapted to favorable conditions before spreading, indicating that climate plays a significant role in these invasions.

Dormancy and risk assessment

This knowledge is crucial for future pest management and invasion prevention strategies, suggesting that existing risk assessment models, which typically overlook dormant phases, need updating. 

“The problem is most of the models that we have for risk assessment to see if the species are going to be invasive and a pest problem in the future don’t account for this lag phase or this dormant phase,” Mesgaran said. “It’s not that they’re not going to be a problem, it’s just the calm before the storm.”

As the research progresses, the team plans to investigate how the native climates of these invasive species compare to their new environments, shedding further light on the mechanisms behind their spread and dormancy.

The study is published in the journal Nature Ecology & Evolution.

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