Monitoring and distribution modelling of invasive species along riverine habitats at very high resolution

Monitoring and species distribution models (SDMs) are increasingly used to support conservation planning but rarely projected at a very high resolution for conservation management. In this study, we compared population distribution and size of five invasive plant species along an 18 km alluvial system in Switzerland, over a period of 11 years. Exhaustive inventories of past (2001) to current (2012) populations showed a massive increase in invaded areas in eleven years. Impatiens glandulifera and Reynoutria japonica were the species with the largest increase in population number and size. The ecological preferences of each species were then modelled at 1 m resolution, using environmental variables expressing topography, disturbances, dispersal, soil texture and light availability. SDMs successfully depicted the niches at very high resolution. Some of the important predictors (e.g., canopy density, distance to river) could not have been valuably used at a coarser resolution. From these very high resolution models, we predicted the potential distribution and abundance of species and were able to derive two indices indicating the amount of habitat still available for future species colonisation, crucial information for management. Large, empty areas were predicted suitable for each species, suggesting that the observed increase in population size may continue in the future. The two proposed range filling indices and abundance models may be used efficiently in future studies at very fine resolution to prioritize eradication efforts in already invaded areas and controls in areas at high risk of invasion. To our knowledge, this is the first study investigating the efficiency of SDMs to predict invasions at such very fine resolution