ARANUIAN VEGETATION HISTORY OF THE ARROWSMITH RANGE, CANTERBURY, NEW-ZEALAND .3. VEGETATION CHANGES IN THE CAMERON, UPPER SOUTH ASHBURTON, AND PADDLE HILL CREEK CATCHMENTS

The vegetation history of three upland valleys in the Arrowsmith Range is deduced from pollen and macrofossil analysis of buried plant debri s and peat, deposited at intervals through the Aranuian period. The ev idence is supplemented by information from dated charcoal layers in th e soils and from surface logs, knowledge of the modem pollen rain, and the present composition and distribution of the woody plant flora. Th e vegetation history is interpreted in the light of episodes of glacia l advance and retreat and periods of alluviation. There are no direct data for reconstruction of early Aranuian (c. 14 000-10 000 yr B.P.) v egetation although probably it was mainly herbaceous. From the beginni ng of the middle Aranuian (10 000-6000 yr B.P.) Phyllocladus alpinus a ssumed dominance. This lasted until very late in the late Aranuian (60 00-0 yr B.P.). In the latter part of the middle Aranuian, Podocarpus h allii was common and Prumnopitys taxifolia was almost certainly presen t, together with various angiosperm tree species. Floristic and geomor phic evidence indicate that climate was wetter than at present in the middle Aranuian. Herbaceous elements increased in the pollen floras ne ar the end of the middle Aranuian and during the late Aranuian. This m ay have been associated with periodic natural fires during a time of d rier climate. About 1850 yr B.P., and during the Polynesian occupation (800-600 yr B.P.), major fire episodes removed almost all tall woody vegetation, initiating the development of the present predominantly sn ow tussock (Chionochloa) grassland cover, with some extensive scrub st ands. Hoheria lyallii is the only common tree now. Other trees and som e shrubs are rare or locally distributed. Phyllocladus alpinus occurs only as single plants or small patches.