Plant Time Bombs: Invasive Species Can Remain Dormant for Extended Period and Pose Hidden Ecological Threat

Invasive plants can remain dormant for decades or centuries after being introduced into an environment before expanding rapidly and wreaking ecological havoc. This was revealed by a new study by experts from the University of California, Davis.

(Photo: Wikimedia Commons/ Michel Langeveld)

How are Invasive Plants Introduced?

Generally, nonnative species are introduced in two ways: by accident or through intentional importation for ornamental, medicinal, agricultural, and other purposes. For example, around 65% of invasive plants were introduced knowingly in California.

According to Mohsen Mesgaran, an assistant professor in the Department of Plant Sciences at UC Davis, this lag phase may have played a significant role. The increase in trade, transportation, and tourism likely contributed to the introduction of non-native plant species.

The longer they stay dormant, the more likely humans are to ignore them. This latency enables them to be overlooked, contributing to their emergence as a serious invasive threat. In short, these plant species act like invasive time bombs.

In the US, ribwort or buckhorn plantain was found to have the longest dormancy. Also known as the common lawn weed Plantago lanceolata, this plant species is noxious to native plants and livestock. It was introduced in the US in 1822 and is now found widely across the country.

Another invasive plant species in the US is the velvetleaf, which was introduced as a possible fiber crop. This plant can be dormant for 50 years before it expands, posing threats to soybean, corn, and other crops as it sucks up water and nutrients from the soil.

Determining Plant Dormancy Periods

Led by Philipp Robeck, the research team investigated over 5,700 species of invasive plants in nine regions worldwide. The study "Invading plants remain undetected in a lag phase while they explore suitable climates" represents the most comprehensive analysis of plant invasions.

The team discovered that almost one-third of the invasive plants they analyzed showed lag periods between introduction and rapid expansion at an average of 40 years. The longest dormant period was 320 years, recorded in sycamore maples in the UK.

The research team generated a list of invasive plants in Great Britain, Japan, Madagascar, Japan, Australia, Ireland, New Zealand, South Africa, and the United States. They used digitized herbaria records to obtain global data on the location and time of species observations.

After that, they looked at trends to determine whether invasive plant species exhibited dormant phases. They also applied a time series analysis to detect lag periods, followed by a second analysis comparing the climate during dormant and expansion phases.

Some plant species that invaded other regions exhibited dormancy periods that varied by location. In 90% of cases, different climate conditions existed during the times when the plant species spread. This indicates that the plants waited for the ideal environmental conditions or learned to adapt to survive a once unsuitable environment.

Considering the future impact of this problem is key to pest management and preventing widespread invasion and economic losses in the coming years. Plant growers, policymakers, and other agencies should also learn to consider dormancy periods in their action plans.