Changes of Vegetation in Southeast Nelson Since the End of the Last Glaciation

Abstract

A sequence and timetable for colonisation by beech forest of land more than 500 m above modern sea level following the end of the Last Glaciation has been determined for the country centred on Lake Rotoroa, Lake Rotoiti and Lake Tennyson in the northern part of the South Island of New Zealand. Peat cores from Lake Tennyson, the Upper Wairau River valley and near Lake Rotoiti were analyzed palynologically and radiocarbon ages from them were used to date regional vegetation changes since 11,800 years BP. During the Last Stadial of the Last Glaciation the treeline was at 500 m above modern sea level and the chief vegetation on the land above 500 m, not covered by ice, was grassland. When the ice retreated, shrubland replaced the grassland and was replaced later by beech (Nothofagus) forest. Beech forest migrated from refuges in the Murchison and Moutere areas into the southeast Nelson area to give the present day cover of beech forest dominated by red beech (Nothofagus fusca), silver beech (N. menziesii) and mountain beech (N. solandri var. cliffortiodes). There is evidence that the colonisation process is not complete and is still continuing in the Upper Wairau River valley.