Talk Invasion by Asian knotweed Fallopia spp along linear landscape features: spatial dynamics and perspectives in mountainous environment

According to IUCN, biological invasions are the second cause of species extinction right after habitat destruction. Among the great variety of alien plant invaders, Asian knotweeds (Fallopia spp.) are considered to be among the worst invasive species in the world, including Europe and North America. A lot of researches have focused on the biology of invasive knotweeds and on the factors explaining their presence, but the factors governing their spatial and temporal dynamics are still poorly known, especially along dispersal and disturbance vectors such as roads or rivers. The same statement could be made for researches on management and control techniques (except for chemical treatments, which are generally unfit for riparian management). Moreover, to our knowledge, there are very few studies that focus on invasive knotweeds dynamics in mountainous environment, and almost none that does it over medium or long time periods.

The diachronic study presented here is part of an on-going project called DYNARP, which aims at evaluating the respective roles of management, biotic and abiotic, and perception factors in the spatial and temporal dynamic of exotic Asian knotweeds at the stand and the landscape scales. More precisely, this study intended to highlight the respective roles of biotic, abiotic and management factors on the spatial coverage evolutions of knotweed stands over 7 years.

We strongly believe that a more accurate understanding of both “natural” and anthropogenic factors governing Fallopia spp. spatial and temporal dynamics is a prerequisite for better knotweed control.

We monitored the evolution of more than 200 knotweed stands distributed over more than 50 sites of the French Alps. Almost every stand was located near a linear landscape features (e.g. roads, rivers) and they were all situated above 800 meters a.s.l.

For each date, stands outlines were drawn using precise GPS records and several vigour attributes were measured to estimate knotweeds performance and the stands’ spatial evolutions. Afterwards, biotic and abiotic data were collected in four directions around the stands, and anthropic influences were assessed by both field analysis and managers surveys. Data were then analysed using regular and advanced statistical techniques.

First results show truly interesting opposite trends of spatial expansion or reduction, explained by different ecological and management processes. Indeed, it appears that if most stands expanded between the 7 years period, a third of them have known a reduction of their surfaces (up to -150m2 when maximum expansion reached +90m2). If human-induced disturbances and the distance from a transport infrastructure seem to play a role on these dynamics, exact effects of studied factors appear to be context-dependant.

Altogether, these results are particularly relevant to improve management strategies especially those that try to prevent the invasion of the still preserved but highly threatened alpine environments.

Exotic knotweeds (Fallopia), invasion ecology, roads, rivers, management, soil, neighbouring vegetation, spatial expansion, performance, landscape, moutains