A 4300-YEAR PALYNOLOGICAL AND SEDIMENTOLOGICAL RECORD OF ENVIRONMENTAL-CHANGE AND HUMAN IMPACT FROM WHARAU-ROAD-SWAMP, NORTHLAND, NEW-ZEALAND

The palynology and sedimentology of the late Holocene Wharau Road Swam p, Northland, are described. Organic sediment began accumulating ca 43 00 yr B. P. in a valley as a result of damming by a basaltic lava flow from nearby Mount Te Puke. Mixed conifer-hardwood forest dominated th e region until major anthropogenic forest clearance dated by radiocarb on at ca 600 yr B. P. Dacrydium cupressinum was the dominant taxon. Ag athis australis was always present until European clearance, with peak s in the pollen record at inferred ages of ca 3700 yr B. P. and ca 180 0 yr B. P. Climate changes similar to those registered in other pollen diagrams from northern New Zealand are evident, and suggest that clim ate was wetter and warmer than at present before 4000 yr B. P. From ab out 2600 yr B. P. climate became drier and cooler, indicated by a decl ine in Ascarina lucida and D. cupressinum. A period of milder and wett er climate from ca 2000 yr B.P. is suggested by increases in D. cupres sinum, A. lucida and Cyathea. Major forest disturbance at ca 600 yr B. P. is recorded by a sharp decline in all tree and shrub taxa accompani ed by increases in herbs and pteridophytes, and a coincident sharp ris e in charcoal influx. Also of particular importance at this time is th e dramatic rise in the curve for Pteridium esculentum (bracken), which is associated with Polynesian land clearance and cultivation. The dat e for forest clearance is much later than the widely accepted date of ca 1000 yr B. P for first settlement. Sedimentological evidence, in pa rticular changes in grain-size distribution, supports palynological in ferences of anthropogenic disturbance of local vegetation and associat ed soil instability. Increased rates of erosion are indicated by sharp rises in coarse grain-size fractions from ca 700 yr B. P. These granu lometric trends are accompanied by changes in sediment chemistry, espe cially potassium and sodium, which show increased concentrations.