Fiordland National Park contains the majority of the largest area of unmodified vegetation in New Zealand. The dense forests, often clinging to steep valley sides, comprise mostly silver beech and mountain beech, but also podocarps. A large variety of shrubs and ferns, often dominated by crown fern, make up a rich understory of plants, with the forest floor covered in mosses and liverworts. The abundant vegetation is supported by the high rainfall, but continues to be damaged by introduced species such as red deer and possum.