Utilization of foreign plant ecosystem engineers is a worldwide strategy to combat land degradation. However, the ability of ecosystem engineers to modulate limiting abiotic and biotic resources of other species can cause serious damage to ecosystems in which they become invasive. Here we use Lupinus nootkatensis (Donn ex Sims) as an example species to estimate and project the hazardous potential of nitrogen fixing herbaceous plants in a sub-polar oceanic climate. L. nootkatensiswas introduced to Iceland in the 1940s to address erosion problems and foster reforestation and subsequently became an important invader.
In a local field survey we quantified the invasion impact of L. nootkatensisat three different cover levels (0 %, < 50 %, 51 – 100 %) upon native plant communities of heath-, wood- and grasslands. Afterwards, we scaled impacts up to the ecosystem and landscape level by relating occurrences of L. nootkatensisto environmental and human mediated variables across Iceland using a species distribution model.
Under current climate conditions, 13.3 % of Iceland's land surface area is suitable lupine habitat. Until 2061 – 2080 this area will more than double and expand significantly into the Central Highlands. Plant diversity was significantly deteriorated under high lupine cover levels of the heath- and woodland. Species richness of the most diverse habitat, the heathland, linearly decreased with lupine cover level. The abundance of small rosettes, cushion plants, orchids and small woody long-lived plants of the heath declined with invader presence, while the abundance of late successional species and widespread nitrogen-using ruderals in wood- and grasslands increased.
Species-rich habitats show a loss of species diversity and richness even in low lupine cover classes. The future increase of suitable lupine habitat might lead to the displacement and eventual extinction of cold-adapted native plant species and will certainly challenge conservation and restoration in Iceland.