Invasives Blog

Sentinel forests are becoming an important and useful tool for monitoring pest behaviours on non-native trees to help predict potential invasive threats in the future (© Pexels)

With increased levels of human development, transportation and changing climates, we are seeing greater instances of invasive species introduction and spread across all continents. Such invasive species can cause significant ecological and economical impacts in targeted areas, for example the elm bark beetle (Hylurgopinus rufipes) which spread across Europe from North American log transports and acted as a carrier for Dutch elm disease which resulted in losses of over 60 million elm trees and its near extinction in countries such as the UK.

The key to reducing the negative impacts of exotic introductions is knowing what species are a threat and what is at risk natively. It is this thinking that has resulted in a group of researchers from Europe, China and the United States to develop and trial a new approach to the early warning of potential threats. The concept is to plant “sentinel trees” native to a specific region and plant them in a non-native location, continuous monitoring of these trees will provide insights into what pests and diseases from the non-native area may be a threat if they were to ever spread into the tree’s land of origin.

A team led by entomologist Alain Roques of the French National Institute for Agriculture, Food and Environment led this approach from 2007 to 2011.  In which time seven species of European trees were planted in Fuyang and Beijing, China. Following years of monitoring, the researchers had identified over 100 species of insects on the European trees, five of which were considered to be a threat. Specimens were taken back to Europe to study further on broad leaved trees under quarantine, which showed that one in particular, the bagworm moth could destroy numerous adult trees in its lifetime. 

Invasive pests and diseases cause major ecological and economic damages globally, by developing monitoring tool such as the sentinel programme, countries and regions can help prepare for new potential invasions (© Pexels)

Although the monitoring and study of these sentinel plantations required many years to complete, the results so far are already having an impact of international policies, notably in trade. In one such sentinel study near Shanghai, a beetle was found feeding on American sweetgum trees, this species is of particular economic and ecological importance for parts of North America therefore if it was to spread onto the continent it could cause major losses. This discovery was reported in 2017 and within the year China banned the import of the trees to avoid the risk of spreading due to human transportation. This spurred the development of further plantations across China in 2018 housing pines, oaks and citrus trees which has resulted in eight species of concern so far.

Governments and funding agencies are recognising the importance of these sentinel schemes, and are boosting support for such projects. The latest approval in Europe with the Holistic Management of Emerging Forest Pests and Diseases is expected to run till 2025 due to recent funding. The U.S. Forest Service is funding several sentinel-themes projects, such as one being led by Ohio State University which will be planting the first sentinel plantation of Asian and European trees (including hollies, maples and pines) in multiple locations across the US.

If you would like to read more on this subject, please see the links below:

Sentinel Trees as a Tool to Forecast Invasions of Alien Plant Pathogens

Sentinel Tree Reporting & Monitoring

The sentinel tree nursery as an early warning system for pathway risk assessment: Fungal pathogens associated with Chinese woody plants commonly shipped to Europe

For information on CABI’s work in this area:

Sentinel nurseries as early warning system against alien tree pests

CABI offers global guidance to help protect the world’s trees and forests from harmful pests and diseases

Field guide for the identification of damage on woody sentinel plants

The unique role of sentinel trees, botanic gardens and arboreta in safeguarding global plant health.

Safeguarding global plant health: the rise of sentinels

Sentinel nurseries to assess the phytosanitary risks from insect pests on importations of live plants

Spotting the pests of tomorrow—Sampling designs for detection of species associations with woody plants

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