Holocene vegetation and environmental reconstructions from swamp deposits in the Dargaville region of the North Island, New Zealand: implications for the history of kauri (Agathis australis)

摘要

Multiproxy analysis of two swamps, representative of numerous sites in the Dargaville area, provide a Holocene record of a transition from flooded marine valleys to freshwater swamp-forests. Dendrochronology of subfossil wood from these and other associated sites provide a record of kauri (Agathis) growth and demise over 3600 calendar years. A discrepancy between the abundance of kauri pollen and the timing of maximum kauri forest development, as revealed by dendrochronology, suggests that kauri pollen abundance at our sites is determined by the wetness of the substrate rather than by proximity of source trees. This finding has implications for the palaeoclimatic interpretation of late Quaternary Agathis pollen curves. Kauri has been present in the Dargaville area for more than 7000 ~(14)C yr BP with suitable conditions for the preservation of wood leading to an apparent expansion in Agathis population after -3600 cal. yr BP rather than representing a southerly migration of this species.