Taxonomic and ecological profiles of rarity in the New Zealand vascular flora

Abstract

Abstract We sought to taxonomically characterise New Zealand's plant rarity within the context of the entire flora, and then to examine any geographical and ecological predispositions the rare flora might possess in terms of elevational and latitudinal range and ecosystem representation. We found skewed frequency distributions in the taxonomic properties of our rare flora, and its threatened and uncommon components, compared with the entire flora. There are more rare dicotyledonous trees and shrubs, dicotyledonous herbs, both composite and non‐composite, and orchids, and fewer rare grasses and sedges than expected at random. Whereas several families and genera have unexpectedly high representation of rare taxa, there is no consistent trend of proportional rarity across a gradient of taxon‐rich‐ness. Forty percent of New Zealand's 433 genera are monospecific and 30% of those contain rare taxa. New Zealand endemism is not significantly different in the rare, threatened, and uncommon floras compared with the entire flora. Taxonomic richness in the rare flora is greater in the coastal and lowland zones than in montane and alpine zones. The majority of rare taxa are confined to one of three latitudinal zones ‐ northern North Island, northern South Island, southern South Island ‐ and the Three Kings, Chatham, and subantarctic offshore island groups. Three broad classes of non‐forest ecosystems below treeline support 70% of the rare flora. Coastal and inland cliffs below treeline feature prominently and provide an incentive for research into neglected ecosystems. Taxonomic and ecological profiles provide information useful in formulating conservation policy and recovery strategies for rare taxa and their ecosystems.