by ETH Zurich
For centuries, human activity has intentionally or unintentionally driven the spread of plant species to areas far outside their native habitat. On average, about 10% of non-native species worldwide become invasive, often causing large ecological and economic consequences for affected regions.
For the first time, a global team of researchers, led by ETH Zurich, have explored which regions on Earth are most vulnerable to non-native tree invasions. The study, published in the journal Nature, combined human, and ecological factors to assess the drivers of tree invasion occurrence and severity across the globe. Ecological factors determine severity
The study reveals that proximity to human activity—especially maritime ports—emerges as a dominant factor driving the likelihood of invasion. Ports handle tons of goods including plants or seeds from all corners of the globe. The colonization pressure exerted by plant material is, therefore, very high in these regions of high human activity. The closer a forest is to a port, the higher the risk of invasion.
However, ecological factors determine the severity of invasion. Most importantly, native biodiversity helps to buffer the intensity of these invasions. In diverse forests, when most of the available niches are filled by native species, it becomes harder for non-native tree species to spread and proliferate.
The ecological strategy of the invading species is also important in determining which types of trees can invade in different regions. In harsh regions with extreme cold or dry conditions, the researchers found that non-native tree species must be functionally similar to native species to survive in these harsh environments.
However, in locations with moderate conditions, non-native trees must be functionally dissimilar to native species in order to survive by functionally differentiating themselves, the non-native species avoid intense competition with native trees for important resources such as space, light, nutrients, or water.