The effect of recent volcanic events and climatic changes on the vegetation of Mt Egmont (Mt Taranaki), New Zealand

Abstract

Pollen diagrams are presented from two mires on the flanks of the recently active andesite stratovolcano of Mt Egmont. The diagrams span the last 3500 years, and record both climatic and volcanic induced changes to the broadleaf-podocarp forests, scrub, and shrublands which clothe the slopes of Mt Egmont and the adjacent Pouakai Range to the north. Libocedrus bidwillii and Weinmannia racemosa are common trees in the upper montane forest. Both have fluctuated in abundance over the past 3500 years, with Libocedrus being most abundant between c. 3000 and 2500 years ago, and c. 1400 and 450 years ago, and Weinmannia more common in the intervening periods. Libocedrus dominance is associated with evidence for slope instability, and it is suggested that it reflects cooler, stormier conditions. There is little evidence for climatically induced vegetation change in the lower montane forests, except that Ascarina lucida became rare after c. 1400 years ago, which many also indicate cooler conditions. The last two major eruptive episodes from Mt Egmont, the first grouped into the Newall Formation (c. 1500 A.D.), and the second principally comprising the Burrell Lapilli (c. 1650 A.D.), disrupted surrounding forest. The Newall eruptions affected forests on the north-west slopes, and the Burrell Lapilli those to the east and south-east. Both events destroyed forest and disrupted canopies, thus giving rise to secondary successions which were at first dominated by Coriaria, but later by dense stands of Weinmannia. It has only been in the last 100 years that these Weinmannia stands have begun to open out and the forest to return to its pre-emption state. Anthropogenic influence is indicated by high levels of Pteridium spores after c. 1500 A.D., a consequence of Polynesian clearance of the coastal lowlands of Taranaki.