LATE HOLOCENE PALYNOLOGY AND PALAEOVEGETATION OF TEPHRA-BEARING MIRESAT PAPAMOA AND WAIHI BEACH, WESTERN BAY OF PLENTY, NORTH-ISLAND, NEW-ZEALAND

The vegetation history of two mires associated with Holocene dunes nea r the western Bay of Plenty coast, North Island, New Zealand, is deduc ed from pollen analysis of two cores. Correlation of airfall tephra la yers in the peats, and radiocarbon dates, indicate that the mires at P apamoa and Waihi Beach are c. 4600 and c. 2900 conventional radiocarbo n years old, respectively. Tephras used to constrain the chronology of the pollen record include Rotomahana (1886 AD), Kaharoa (700 yr B.P.) , Taupo (Unit Y; 1850 yr B.P.), Whakaipo (Unit V; 2700 yr B.P.), Stent (Unit Q; 4000 yr B.P.), Hinemaiaia (Unit K; 4600 yr B.P.), and rework ed Whakatane (c. 4800 yr B.P.) at Papamoa, and Kaharoa and Taupo at Wa ihi Beach. Feat accumulation rates at Papamoa from 4600 - 1850 yr B.P. range from 0.94 to 2.64 mm/yr (mean 1.37 mm/yr). At Waihi Beach, from 2900 yr B.P. - present day, they range from 0.11 to 0.21 mm/yr (mean 0.20 mm/yr). Feat accumulation at both sites was slowest from 1850 to 700 yr B.P., suggesting a drier overall climate during this interval. At both sites, the earliest organic sediments, which are underlain by marine or estuarine sands, yield pollen spectra indicating salt marsh or estuarine environments. Coastal vegetation communities declined at both sites, as sea level gradually fell or the coast prograded, and we re eventually superseded by a low moor bog at Papamoa, and a mesotroph ic swamp forest at Waihi Beach. These differences, and the marked vari ation in peat accumulation rates, probably reflect local hydrology and are unlikely to have been climatically controlled. The main regional vegetation during this period was mixed northern conifer-angiosperm fo rest. Kauri (Agathis australis) formed a minor component of these fore sts, but populations of this tree have apparently not expanded during the late Holocene at these sites, which are near its present southern limit. Occasional shortlived forest disturbances are detectable in the se records, in particular immediately following the deposition of Taup o Tephra. However, evidence for forest clearance during the human era is blurred by the downward dislocation of modern adventive pollen at t hese sites, preventing the clear differentiation of the Polynesian and European eras.