Figure 2: Research on the processes underlying biotic invasions (systems knowledge) increasingly
considers human agency as an important explanatory factor. The picture shows a subalpine grassland
at the slope of Mauna Kea in Hawaii covered in alien grasses and herbs. The past land use of this
area as a cattle ranch, that involved the deliberate sowing of grazing-adapted alien species and the
accidental introduction of further alien species as contaminants of the seed, helps to explain the
invasion of alien species such as Holcus lanatus, Plantago lanceolata, Senecio madagascariensis or
Verbascum thapsus in these areas (Photo by Eva Schumacher).