MCGLONE:Available on-line NEW at: ZEALANDhttp://www.newzealandecology.org/nzje/ POSTGLACIAL WETLANDS 1 REVIEW Postglacial history of New Zealand wetlands and implications for their conservation Matt S. McGlone Landcare Research, PO Box 40, Lincoln 7640, New Zealand (Email:
[email protected]) Published on-line: 9 March 2009 ___________________________________________________________________________________________________________________________________ Abstract: Most New Zealand wetlands formed at or after the end of the last glaciation (c. 18 000 cal yrs BP). Those associated with major rivers and close to the coast tend to be young as erosive processes both destroy and initiate wetlands. However, there is a strong linear trend in initiations since 14 000 cal yrs BP, which suggests that geomorphic processes such as soil deterioration, landslides, sand dune movement and river course changes are constantly adding new, permanent wetlands. Most wetlands began as herbaceous fens but usually transitioned to shrub- or forest-covered bog–fen systems, in particular after the beginning of the Holocene (11 500 cal yrs BP). Raised bogs formed from fens during the late-glacial and early Holocene, when river down-cutting isolated them from groundwater inflow. As climates warmed through the late-glacial and early Holocene, wooded wetlands spread and over 75% of lowland peat profiles preserve wood layers. Large basins with high water inflow often contain lakes or lagoons and have maintained herbaceous swamps, whereas those with limited catchments have become almost entirely covered with forest or shrubs. Wetlands in drier districts tend to have been initiated during the mid- and late Holocene as the climate cooled and rain-bearing systems penetrated more often.