Distribution of Asian knotweeds on the Rhône River basin, France: A multi-scale model of invasibility that combines biophysical and anthropogenic factors.

Biotic and abiotic factors are important drivers of the introduction, dispersal and establishment of an invasive species in fluvial corridors. In this study, we propose to better understand the spatial distribution of Asian knotweeds and to model their invasibility at the river basin scale in the Rhône Mediterranean and Corsica regions, France. We implemented a multiscale analysis of biophysical and anthropogenic factors related to the presence of knotweeds. Subbasins were sampled (50-600 km2), a large dataset on knotweed occurrence and biotic/abiotic factors was collected, and logistic regression was applied. A robust logit model (accuracy: 90%; false positive rate: 13%) estimated the probability of the occurrence of knotweeds at the river basin scale. We found clear evidence of: i) spatial scale-dependent water availability for knotweed implantation (e.g., summer vs. winter rainfalls > 250 mm); ii) an important role of hydrogeomorphic forces in dispersal; and iii) interspecific competition in riparian areas. The occurrence of knotweeds is also closely related to human-derived pressures. The management of knotweeds on roads and railways in the vicinity of rivers may be a major source of propagules. Hydraulic infrastructures (dikes and mill weirs) may also have served as locations of knotweed introduction since the end of the nineteenth century and may play a major role in the propagule transfer of knotweed; to date, these infrastructures have provided favourable conditions for knotweed establishment. Despite local water authorities' increasing awareness of invasive plants, local management practices for flood mitigation, low awareness of roads/railway managers, and negative representations of knotweeds have probably largely contributed to their dispersion over decades. The final model intends to integrate these biophysical and human factors by providing an operational tool to help river managers determine the sensitivity of their river basins to knotweed invasion.

Landscape perceptions and social representations of Fallopia spp. in France.

Choices have to be made to manage invasive species because eradication often is not possible. Both ecological and social factors have to be considered to improve the efficiency of management plans. We conducted a social study on Fallopia spp., a major invasive plant taxon in Europe, including (1) a survey on the perception of a landscape containing Fallopia spp. using a photoquestionnaire and (2) an analysis of the social representations of Fallopia spp. of managers and users in one highly invaded area and one less invaded area. The respondents to the photoquestionnaire survey appreciated the esthetics of the landscapes less when tall Fallopia spp. were present. Few people were able to identify and name the plant, and this knowledge negatively affected the appreciation of the photos containing Fallopia spp. The central core of the social representation of Fallopia spp. was composed of the invasive status of the plant, its density, and its ecological impacts. The peripheral elements of the representation depended on the people surveyed. The users highlighted the natural aspect whereas the managers identified the need for control. In the invaded area, the managers qualified the species as "unmanageable," whereas the species was qualified as "foreign" in the less invaded area. Those results provide insights that have to be included when objectives of management plans of these species are selected.

Effects of endogenous ABA levels and temperature on cedar (Cedrus libani Loudon) bud dormancy in vitro.

Axillary and apical buds of in-vitro-propagated cuttings of Cedrus libani are unable to burst at 24 °C, but this inhibition was overcome at 30 °C. Here we have used cedar microcuttings to investigate whether the levels of endogenous hormones vary with bud dormancy and temperature. We analysed the levels of abscisic acid, indole-3-acetic acid, zeatin, isopentenyladenine and their major metabolites using HPLC purification and fractionation of the samples coupled to an ELISA method for hormonal quantitation involving several antibodies elicited against each hormonal family. Abscisic acid levels in microcuttings with dormant buds were higher than those in microcuttings with growing buds. At 24 °C, needles accumulated more abscisic acid than at 30 °C. In addition, when needles were removed, but growth release was achieved at 24 °C. Abscisic acid supplied at 30 °C induced the formation of dormant buds. These results suggest that abscisic acid accumulation in the needles can explain the bud dormancy of cedar microcuttings at 24 °C.