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Modelling and mapping

Modelling and mapping risks of invasive forest pests

Invasive species of forest insects, diseases and plants have threatened Canada’s forested areas and urban environments for well over a century. Pests such as chestnut blight and Dutch Elm Disease, have had severe impacts on certain native Canadian tree species, in some cases almost eliminating them. Today, the emerald ash borer, first observed in Canada in 2002, poses a serious threat to ash trees across North America.

Strategies to eliminate or slow the spread of these destructive pests can be costly. However, risk assessment and mapping tools can lead to more timely decisions, effective deployment of resources for pest surveillance and control, and the development of sound policies for dealing with new and anticipated invasive pests.

Models for calculating risks from alien invasive forest species recreate a dynamic process of pest invasion across large, geographically diverse areas, based on what is known about current locations of the pest, points of entry, distribution of susceptible hosts and potential human-assisted movement pathways along major transportation corridors.

The resulting maps give a picture of the predicted rate and pattern of spread, providing managers with an important decision support tool for immediate control or slow-the-spread measures. The information generated can also be useful in raising awareness about new invasive pests.

A tool to help manage the risk

The Forest Invasive Alien Species (FIAS) Pathway Explorer is a web-based tool that maps probabilistic pathways along which invasive pests could be introduced by human activities such as international and domestic trade, transportation and recreation.

Mapping risks and uncertainties of new invasive threats

Developing risk models for recently established invasive pests is challenging, however, because information about their behaviour, life cycle and likelihood of survival in the North American climate is generally scarce.

In collaboration with researchers from USDA Forest Service, North Carolina State University and Technion (Israel Institute of Technology), Canadian Forest Service (CFS) researchers have developed new risk mapping techniques that incorporate knowledge gaps about an invasive pest.

The new approach takes into account what is known and what has to be known about the pest to make reliable assessments and estimates how much uncertainty the risk maps can tolerate without losing their value for decision-making.

The new methodology incorporates an uncertainty model that characterizes what is believed to be unknown about the new threat. Analyses consider the potential knowledge gains from unexpected finds of the invasive organism—detections that were not predicted by the standard risk model.

The new approach has been used to map risks and broad-scale surveillance priorities for Sirex woodwasp in eastern North America.

Broad-scale surveillance priorities for Sirex woodwasp in eastern North America. A comparison of the two maps shows that as knowledge about the pest increases (from poor to average), surveillance priorities change.

Figure 1. Broad-scale surveillance priorities for Sirex woodwasp in eastern North America. A comparison of the two maps shows that as knowledge about the pest increases (from poor to average), surveillance priorities change.

Predicting the human-assisted spread of invasive pests

In addition, CFS researchers in collaboration with their counterparts in the U.S. have developed maps that portray the potential human-mediated dispersal of alien invasive species across both Canada and the U.S. The models take into account human-assisted movement of invasive pests through transportation corridors, as a result of international and domestic trade and other economic activities (such movement of firewood with recreation and campground visits).

These analyses are particularly helpful in finding ways to mitigate human-assisted introductions and movement of new invasive pests. They identify the most likely gateways for human-assisted arrivals and movement of the pests, information that is essential for prioritizing surveillance and regulation efforts once a pest has arrived or is anticipated to enter North America. They can also assist in making regulatory decisions, such as potential phytosanitary restrictions or domestic quarantines.

Assessing economic impacts

Another important component of risk assessment is predicting the critical points at which an outbreak becomes economically threatening. CFS researchers have developed a forest-sector risk metric for alien species invasions that quantifies the impact of an invasion on economic activities that may be threatened by an outbreak.

The researchers examined the possible infringements on regional annual allowable cut levels as a way to estimate the potential economic impact of the invasive pest to the forest products sector. Their dynamic model for Sirex woodwasp takes into account invasion spread, host tree mortality, wood supply distribution and present-day harvest activities and can be adjusted as new information about the pest becomes available.

The point at which the invasion begins to threaten sustainable forest harvesting levels at a broad scale could become an important indicator for decision-makers and regulators, particularly in developing and instigating control measures.

Developing user-friendly tools

The new risk mapping techniques still require significant technical expertise. However, CFS researchers are working to develop more practical, user-friendly risk mapping and assessment tools that can help analysts, forest practitioners, pest management professionals and regulators to better estimate risks and uncertainties of new invasive threats.

Ultimately, these models will also incorporate future changes in climate, economic activities, changes in regulations, levels of international and domestic trade and the availability of new biological control techniques.

Canadian Forest Service key contact

Denys Yemshanov, Research Scientist - Quantitative Spatial Modeler

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