Improving management of Asian knotweeds alongside transport routes

In France and across Europe, Asian knotweeds are some of the most invasive species. Once transferred from their area of origin to a new area, they develop quickly and profusely, limiting the growth of other plants. In addition to their impact on biodiversity, the knotweeds that prefer spaces shaped by humans and especially transport routes (roads, railways, inland waterways) also present a risk to the safety of these structures. Currently, actions taken to manage these risks are expensive. However, despite current methods, the plants continue to spread.

To provide insight into the growth of knotweeds around transport routes, the Dynarp project took place over four years and involved a group of ecologists, geomaticians 1, sociologist-geographers and space management experts. "The Dynarp project is unusual due to its interdisciplinary approach and unique because of its objective to understand the behavior of knotweeds, specifically in relation to transport infrastructure, and to consider better management methods," specifies André Evette, project leader and researcher at the Irstea Grenoble Center. Scientists approached the research in three ways:

  • Analyzing the way in which infrastructure managers perceived knotweeds and how this perception affected their actions;
  • Defining the links between the form and density of knotweed beds or "patches," the type of infrastructure and the associated management methods, along with the environmental factors that encourage their growth;
  • Evaluating the relevance of remote sensing tools to map the beds and their application to on site management methods.

A national survey of infrastructure managers

The study included a particularly original approach, a survey of the organizations responsible for managing roads, railways and inland waterways throughout the country (interdepartmental road divisions, municipalities, motorway managers, SCNF network, Voies Navigables de France, etc.). Following the results of a questionnaire (over 200 answers collected) and an image questionnaire to analyze the perception of managers, several lessons were learned. These included:

  • different perceptions according to the type of infrastructure being managed. Road and river managers were prepared to act earlier in the plant's development compared to railway managers. Additionally, river managers were more motivated by biodiversity and landscape conservation issues than their railway and road counterparts, who were more focused on safety.
  • Most managers were dissatisfied by current action methods (lack of action, coordination and means) and discouraged by the poor effectiveness of actions undertaken.


Multiple scientific advances

Striking results were obtained for plant ecology in infrastructure landscapes. After mapping 600 knotweed patches using centimetric resolution on sites crossed by the three types of infrastructure (total surface of 7 hectares), relationships between the shape and size of the patches and the type of infrastructure (and associated management methods) were defined. Knotweed plants were found closer to rivers than roads, and they were more spread out along roads than railways. This important information helps us evaluate knotweed responses to the management methods used.

Monitoring the spatial development of the plant itself was used to identify the influence of various factors, such as the initial size of patches (as their growth is proportional to the surface area covered seven years earlier) or the distance between plants and the road (proximity limits growth). By monitoring plants over several years and using data relating to the speed of patch growth and spatial organization, work was carried out to define models simulating species dynamics to help improve management practices over time.

Finally, remote sensing tools were assessed, confirming the relevance of satellite and drone imaging in mapping knotweed beds, although their use is difficult to transfer to land management.

New tools for managers

Using results from the study and expertise from the project's partners, a guide was created for managers of transport infrastructure. Its aim is to provide recommendations for implementing knotweed management plans adapted to each structure. Divided into five invasion levels, these recommendations aim to guide managers in deciding whether to intervene or not, and to help them chose an appropriate response in relation to the situation (density and surface area of beds compared to risks). "We hope this guide will lead to more efficient management by helping stakeholders ask the right questions to take cost-effectiveness into account. The aim is no longer to reject knotweeds, as we can't eradicate them, but to study the most appropriate and reasonable solutions," concludes André Evette. The guide and GIS mapping tools (and video tutorials) developed during the project are now available for managers.

Project profile
  • Name: DYNARP - Dynamics and management of Asian knotweeds across landscapes, impacts and perceptions
  • Scientific coordination: André Evette, Irstea Grenoble
  • Dates: September 2014 - January 2018
  • Partners: Irstea, CEREMA, UMR 5600 Environment City Society, Concept Cours d’Eau
  • Total cost: €490,000
  • Funding: Ministry for Environmental and Inclusive Transition and ADEME, ITTECOP program / Foundation for Biodiversity Research / Linear and Biodiversity Infrastructure Club / Irstea

For more information

1 - Geomatics refers to the tools and methods used to acquire, analyze and distribute geographical data, also known as spatial or geospatial data.