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Five new pollen diagrams from 4420 m, 3910 m, 3550 m, 3500 m and 2740 m on Mt Wilhelm, Papua New Guinea, are presented. This altitudinal sequence coupled with extensive ¹⁴ C dating allows a quite accurate determination of the position of vegetation zones through time. From more than 22 000 years ago until 10 200 yrs B.P. the tree-line stood well below 2700 m and glaciers were present on the mountain, although ice retreat commenced about 14-15 000 years ago. Forests then colonized the mountain to at least 4000 m by 8500 yr B.P., and the area of Alpine grasslands became restricted. After 5000 yr B.P. the forest retreated slightly to its present limit of 3800-3900 m and grasslands spread, particularly in the last 1000 years when increasing disturbance of the forests by man took place. Before 10 000 yr B.P. cold and probably drier conditions than present are inferred for areas above 2500 m, with possibly …