Trees and shrubs do not grow in these conditions. There are only two species of flowering plants that occur in Antarctica, the Antarctic hair grass and Antarctic pearlwort. These arise along the warmer parts of the Antarctica Peninsula and in the South Orkney Islands and the South Shetland Islands. Human activities such as whale and seal hunts and the more recent waves of tourists have unintentionally carried non-native species into these regions. Invasive species are the biggest threat to the native flora of Antarctica.