Biogeography and phylogenetic structure of the New Zealand tree flora

Abstract

The indigenous New Zealand tree flora includes ca. 400 species (± 200, depending on the definition employed), accounting for ca. 0.6% of the global richness. Approximately 50% of these are asterids, 25% rosids, and the remaining 25% a mix of magnoliids, Chloranthales, monocots, conifers and ferns. Forty-four species are capable of growing into canopy trees. At the time of human colonisation indigenous forest trees are estimated to have covered ca. 82% of the land area of New Zealand, while present day coverage has reduced to ca. 23% (including ca. 11.5 billion trees). The extant tree flora is the result of ca. 93 historical colonisation events, with 82 of these having a mean age in the Late Oligocene or later (< 28.1 Ma), highlighting the importance of long-distance dispersal events in generating this tree assemblage. Most of these arrivals (ca. 70%) are likely to have originated from Australia and the broader South Pacific. This thesis aims to use this tree flora as a testbed for addressing fundamental questions in biogeography, evolution and community assembly, as well as testing modern molecular ecology techniques such as environmental DNA (eDNA). Towards this phylogenetic and phylogeographic structuring analyses of focal taxa (including New Zealand Ericaceae, Agathis, Avicennia, Dacrycarpus, Dacrydium, Geniostoma, Nestegis, Prumnopitys, Pseudopanax and Rhopalostylis) and communities (on Hauturu-ō-Toi, in the Hauraki Gulf) were carried out. Analyses of trnL eDNA were also performed on soil samples taken from forest vegetation plots. The results are outlined and discussed in light of such lenses as: species co-occurrence, comparative phylogeography, phylogenetic community structure and biodiversity monitoring efficacy.