comparison of sedimentation and environmental change in New Guinea shallow lakes

Contemporary mires in the equatorial rainforest of Malesia have envolved from shallow lakes. Often these occupy karstic basins in ultrabasic or volcanic rocks. There is a marked diference in the rate of infilling of the lakes, depending on the degree to which nutrient accession from allochthonous sediments has occurred. Some lakes have infilled slowly with no allochthonous input; these variations in the rate of sedmentation reflect the controls of climatic change and human modification of the catchment. Others have infilled very rapidly, and in these the role of tephra fall is crucial. Thes boost to nutrient levels offorded by periodic tephra fall is reflected in the changes recorded in limnic sediment and terrestrial pollen derived from the surrounding vegetation. An episodic decline in Nothofagus and other pollen reflects the increase in floristic and structural complexity of the rainforest vegetation in the absence of disturbance. Catchment instability, either from tephra fall or landslips. creates opportunities for new generations of tress within a climatic regime which is variable but relatively unchanged through time.