Scientists have been wondering for a long time why some exotic species become invasive while others do not. A new paper we just published on invasive and non-invasive plant species in Belgium reveals that the answer should be sought at the smallest scale. The authors, a team lead by ecologists from the University of Antwerp, indeed showed that there is a lot of variation in conditions at the local scale, and that each different habitat favors different traits in the exotic species. The exercise revealed many of the standard culprits that make habitats vulnerable (like temperature, light availability, native plant species diversity and soil fertility) and non-natives successful (like plant size, photosynthesis ability and nutrient status), yet invasive species were much better at matching their traits with the environment at the local scale than their non-invasive counterparts. Most invasive species indeed managed to produce many more seeds than the non-invasive species, and that even in habitats normally considered less easy to invade, as long as they locally had the correct trait arsenal to deal with these aversive conditions.

Invasive plant species, like this Impatiens glandulifera (Himalayan balsam) in Belgium, often produce many more seeds than their non-invasive counterparts, yet their invasive success largely depends on finding the perfect match between their own traits and the local site conditions.

This shows that the fight between invasive plants and the native vegetation is likely to be won at the smallest scale, with invasive plants cherry-picking sites that best match their characteristics. Unfortunately, it also means that predicting the invasive success of plant species did not become any easier. Yes, exotic plant species with a higher seed production are much more likely to be invasive, yet this seed production itself is at the small scale highly influenced by the match between both habitat conditions and the other traits of the plants. And as the study shows, this local match-making often has some surprises up its sleeve.

Fallopia japonica (Japanese knotweed) has been a highly successful invasive species in Europe, partly due to its flexible adaptation to different environmental conditions.

Reference

Lembrechts JJ, Rossi E, Milbau A, Nijs I (2018). Habitat properties and plant traits interact as drivers of non-native plant species fitness at the local scale. Ecology and evolution.