Palynology, vegetation and climate of the Waikato lowlands, North Island, New Zealand, since c. 18,000 years ago

The vegetational and climatic history of the Waikato lowlands during the last c. 18,000 years is inferred from the palynology of sediment cores from Lakes Rotomanuka, Rotokauri, and Okoroire. Intra‐ and inter‐lake correlations were aided by multiple tephra layers interbedded with the lake sediments. The detailed chronological resolution given by these tephra sequences shows that late glacialpost glacial vegetational and climatic changes were nearly simultaneous throughout the Waikato lowlands. From c. 18,000 to just before 14,000 radiocarbon years ago, the region remained largely unforested. There were successive peaks of herb and shrub taxa: Gramineae, Phyllocladus, Halocarpus, Coprosma . Tree taxa, mostly Nothofagus and Libocedrus , increased, probably because the harsh climates ‐ windy, relatively dry and cool ( c. 4°C below present temperatures)‐were gradually abating. Tall podocarp trees were rare but not absent from the region. Reafforestation proceeded rapidly, beginning c. 14,500 years ago soon after th(~ deposition of Rerewhakaaitu Ash. The earliest forests were dominated by Prumnopitys taxifolia and, until c. 13,000 years ago, the persistence of N. menziesii suggests that temperatures may have been as much as 3°C colder than present. After that time, N. menziesii disappeared and Dacrydium predominated, reflecting a trend towards moister and warmer conditions. From c. 11,000 years ago the expansion of angiosperms (especially Metrosideros, Nestegis and Ascarina ) and tree ferns within Dacrydium ‐dominated assemblages is consistent with evidence from elsewhere in New Zealand of an early postglacial period of maximum wetness and warmth. However, by c. 8,500 years ago, Ascarina was already declining, perhaps because of increased frostiness or droughtiness, or both. Regular cycles in the Dacrydium pollen curves are interpreted to result from abundant emergent D. cupressinum trees being felled by low frequency, high intensity storms. From c. 5,500 years ago this drying trend continued as indicated by rarity of Ascarina , increases of Phyllocladus and Agathis , more microscopic charcoal, and decreases of Dacrydium relative to the other tall podocarps. At all three sites Agathis is most prominent after c. 3,000 years ago, reaching maximum levels c. 1,000 years ago. Many tree taxa (most notably Agathis at Lake Rotokauri) were adversely affected by Polynesian burning. The earliest recorded fires were about 800 years ago.