It has long been recognized that most mountains higher than 3,800 m in New Guinea were formerly glaciated. this thesis reports an investigation of the vegetation beyond the margins of the glaciers at the time of the last maximum advance, and of the subsequent history of this vegetation as it migrated higher onto areas left bare as the ice related. Mt Wilhelm, 4,510 m, 5 47's, 145 01'E, was chosen
... [Show full abstract] because the modern vegetation there is better known than elsewhere in New Guinea. The technique of pollen analysis of sediment raised from mires and trans was employed. to support the interpretation of the results, a study was made of the relationship between the modern vegetation and modern pollen deposition in a wide range of plant communities at different altitudes. This study, reported in Chapters 3-6, shows how percentages of pollen types can be related to particular plant communities, pollen transfer mechanisms and climatic processes. Four sediment sections from sites at 4,420 m, 3,910 m, 3,550 m and 2,740 m altitude were obtained for pollen analysis and 14c dating. (chapters 7-10). The lowest site was situated below the limits of former glaciation and provided a record over the last 22,000 years. The higher sites were exposed by ice retreat that took place between 14,000 and 9,000 years ago. The vegetation history provided by the sites is described and compared with palaeoenvironmental data from elsewhere in New Guinea (chapters11-12). A tentative reconstruction of the palaeoenvironmens suggests that before 10,000 BP cooler and drier conditions prevailed in the mountains. the glaciers retreated after 14,000 BP but the vegetation indicates that cold conditions persisted during this retreat. It is possible that a weakened circulation and dry southeasterly winds were responsible for the climate, and these were partly related to the presence of a dry land area joining Australia and New Guinea. By 8,300 BP, subalpine forests colonised Mt Whilhelm up to 4,000 m, but at 5,000 BP the treeline retreated to its present position at about 3,800 - 3,900 m. Forest at lower altitudes also changed after 6,500 - 5,000 BP. These forests were extensively cleared after 800 BP when planting of gardens took place below 2,500 m. At about the same time grasslands began to replace the subalpine forest. the changes that took place after 6,500 BP can be attributed either wholly to man, or else partly to a deterioration in climate which caused glacier advances in West Irian and a possible increase in erosion on the summit of Mt Wilhelm. The evidence is insufficient to distinguish between the effects of climate change and the activities of man.