Contribution of remote sensing for the inventory of Japanese knotweed (Reynoutria complex) along watercourses: the example of the Azergues River

Abstract

Monitoring Japanese knotweed along watercourses is an important management component for communities. Its objective is to identify the first patches of Japanese knotweed at an early stage before they spread in the environment. When they are already well established, exhaustive cartography monitoring of its propagation along the corridor is often necessary to better contain it. Remote sensing techniques have recently been proposed in the scientific literature, they would significantly reduce the costs related to its monitoring. This paper presents an evaluation of this remote sensing tool along the Azergues, a tributary of the lower Saône already heavily colonized by these plants. A detection of knotweed using IGN (acronym for the French National Institute of Geographic and Forestry Information) aerial orthophotos in the visible and infra-red was conducted and evaluated at two spatial scales: a few hundred meters of watercourse and then at the scale of the watercourse, i.e. several tens of kilometers. This analysis enabled us to identify the current advantages and limitations related to the use of this tool by scientists and managers.