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 tonnes 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.
Native biodiversity is a strong defence
Overall, the study highlights the importance of native tree diversity in helping to limit the severity of these invasions. “We found that native biodiversity can limit the severity or intensity of non-native tree species invasions worldwide,” says Camille Delavaux, lead author of the study. “This means that the extent of invasion can be mitigated by promoting greater native tree diversity.”
The findings have direct relevance for efforts to manage ecosystems in the fight against biodiversity loss across the globe. “By identifying regions that are most vulnerable to invasion, this analysis is useful for designing effective strategies to protect global biodiversity,” says ETH Zurich professor, Thomas Crowther. A large consortium of researchers took part in the study and collected valuable data. “Without the incredible cooperation of scientists around the world, this global perspective would not have been possible.”