Impacts of alien invasive plants on resident species, communities and ecosystems: a global assessment

Background/Question/Methods

There is a growing body of literature assessing the impact of alien invasive plants on resident species and ecosystems, but a comprehensive assessment of the relationship between alien species traits and environmental settings of invasion on the characteristics of impacts was missing. Based on 287 publications with 1551 individual cases that addressed the impact of 167 alien plant species belonging to 49 families, and using data mining methods, we produced the first global overview of frequencies of significant and non-significant ecological impacts and their directions on 15 outcomes related to the responses of resident populations, species, communities and ecosystems.

Results/Conclusions

Species and community outcomes tend to decline following invasions, especially those for plants, but the abundance and richness of the soil biota, as well a concentrations of soil nutrients and water, more often increase than decrease following invasion. Alien invasive plants exert consistent significant impacts on some outcomes (survival of resident biota, activity of resident animals, resident community productivity, mineral and nutrient content in plant tissues, and fire frequency and intensity), while for outcomes at the community level (such as species richness, diversity, and soil resources), the significance of impacts is determined by interactions between species traits and the biome invaded. The latter outcomes are most likely to be impacted by annual grasses, and by wind-pollinated trees invading Mediterranean or tropical biomes. Alien plants are far more likely to cause significant impacts on resident plant and animal richness on islands rather than mainland. One of the important conclusions of this study is that there is no universal measure of impact and the pattern observed depends on the ecological measure examined. Although impact is strongly context-dependent, some species traits, especially life-form, stature and pollination syndrome, may provide a means to predict impact, regardless of the particular habitat and geographic region invaded.