of interspecific and intraspecific hybridisation in New Zealand plants and animals. The two sources of New Zealand's biodiversity following separation from Gondwana have been speciation and air- or sea-borne immigration. Most of these immigrants have arrived from Australia, and have provided the majority of New Zealand's birds and bats as well as some plant species (carried on the wind or inside the guts of birds). Some of these immigrants arrived long enough ago that their affinities to their Australian ancestors are uncertain; for example, the affinities of the unusual short-tailed bats (Mystacinidae) were unknown until fossils from the Miocene were found in Australia. Cyanoramphus parakeets are thought to have originated in New Caledonia and have been successful at reaching many islands in the region. The link between the two island groups also includes affinities between skink and gecko families. Elements Floral biodiversity The history, climate and geology of New Zealand have created a great deal of diversity in New Zealand's vegetation types. The main two types of forest have been dominated by podocarps and southern beech. Podocarps (Podocarpaceae), an ancient evergreen gymnosperm family of trees, have changed little in the last 190 million years. Forests dominated by podocarps form a closed canopy with an understory of hardwoods and shrubs. The forests of southern beeches, from the genus Nothofagus, comprise a less diverse habitat, with the beeches of four species dominating the canopy and allowing a single understory. In the north of New Zealand the podocarp forests were dominated by the ancient giant kauri. These trees are amongst the largest in the world, holding the record for the greatest timber volume of any tree. The value of this was not lost on early European settlers, and most of these trees were felled. The remaining vegetation types in New Zealand are grassland of grass and tussock, usually associated with the subalpine areas, and the low shrublands between grasslands and forests. These shrublands are dominated by daisies, which can become woody and 3 m high. New Zealand had a 2019 Forest Landscape Integrity Index mean score of 7.12/10, ranking it 55th globally out of 172 countries. In addition to terrestrial plants, New Zealand is home to many species of algae. Many species of southern bull kelp are found along the coasts of the main islands, Chatham Islands and the Subantarctic Islands. Faunal diversity Until 2006, it was thought that no mammals, other than